Jon Chorover

Interests

Teaching

Chemistry as applied to environmental systems.

Research

Molecular environmental chemistry and biogeochemistry. Behavior of natural and xenobiotic compounds in complex environmental systems including soil, sediment and water.

Courses

Scholarly Contributions

Books

• Dontsova, K., Balogh-Brunstad, Z., & Le, R. G. (2020). Biogeochemical Cycles: Ecological Drivers and Environmental Impact. John Wiley \& Sons.

Chapters

• Dontsova, K. M., Balogh-Brunstad, Z., & Chorover, J. D. (2020). Plants as Drivers of Rock Weathering. In Biogeochemical Cycles: Ecological Drivers and Environmental Impact(pp 33-58). Wiley.
• Moravec, B., & Chorover, J. (2020). Critical Zone Biogeochemistry: Linking Structure and Function. In Biogeochemical Cycles: Ecological Drivers and Environmental Impact(pp 131--149). Wiley Interscience.
• Zaharescu, D. G., Burghelea, C. I., Dontsova, K., Reinhard, C. T., Chorover, J., & Lybrand, R. (2020). Biological weathering in the terrestrial system: an evolutionary perspective. In Biogeochemical cycles: ecological drivers and environmental impact(pp 1--32).
• Chorover, J. D., Root, R. A., & Kong, S. (2018). Organic acid effect on arsenate bioaccessibility in gastric and alveolar simulated biofluid systems. In Environmental Arsenic in a Changing World. CRC Press.
• Troch, P. A., Zeng, X., Van Haren, J. L., Tuller, M., Sibayan, M., Schaap, M. G., Saleska, S. R., Ruiz, J., Rasmussen, C., Pohlmann, M. A., Pelletier, J. D., Monson, R. K., Maier, R. M., Kim, M., Huxman, T. E., Ferre, P. A., Durcik, M., DeLong, S. B., Cueva, A., , Chorover, J. D., et al. (2017). Controlled Experiments of Hillslope Coevolution at the Biosphere 2 Landscape Evolution Observatory: Toward Prediction of Coupled Hydrological, Biogeochemical, and Ecological Changes. In Hydrology of Artificial and Controlled Experiments. Rijeka, Croatia: IN TECH d.o.o.
• Troch, P. A., Zeng, X., Van Haren, J. L., Tuller, M., Sibayan, M., Schaap, M. G., Saleska, S. R., Ruiz, J., Rasmussen, C., Pohlmann, M. A., Pelletier, J. D., Monson, R. K., Maier, R. M., Kim, M., Huxman, T. E., Ferre, P. A., Durcik, M., DeLong, S. B., Cueva, A., , Chorover, J. D., et al. (2018). Controlled Experiments of Hillslope Coevolution at the Biosphere 2 Landscape Evolution Observatory: Toward Prediction of Coupled Hydrological, Biogeochemical, and Ecological Changes. In Hydrology of Artificial and Controlled Experiments, Jiu-Fu Liu and Wei-Zu Gu. Rijeka, Croatia: IntechOpen. doi:10.5772/intechopen.72325
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  Understanding the process interactions and feedbacks among water, porous geological media, microbes, and vascular plants is crucial for improving predictions of the response of Earth’s critical zone to future climatic conditions. However, the integrated coevolution of landscapes under change is notoriously difficult to investigate. Laboratory studies are limited in spatial and temporal scale, while field studies lack observational density and control. To bridge the gap between controlled laboratory and uncontrollable field studies, the University of Arizona built a macrocosm experiment of unprecedented scale: the Landscape Evolution Observatory (LEO). LEO comprises three replicated, heavily instrumented, hillslope-scale model landscapes within the environmentally controlled Biosphere 2 facility. The model landscapes were designed to initially be simple and purely abiotic, enabling scientists to observe each step in the landscapes’ evolution as they undergo physical, chemical, and biological changes over many years. This chapter describes the model systems and associated research facilities and illustrates how LEO allows for tracking of multiscale matter and energy fluxes at a level of detail impossible in field experiments. Initial sensor, sampler, and soil coring data are already providing insights into the tight linkages between water flow, weathering, and microbial community development. These interacting processes are anticipated to drive the model systems to increasingly complex states and will be impacted by the introduction of vascular plants and changes in climatic regimes over the years to come. By intensively monitoring the evolutionary trajectory, integrating data with mathematical models, and fostering community-wide collaborations, we envision that emergent landscape structures and functions can be linked, and significant progress can be made toward predicting the coupled hydro-biogeochemical and ecological responses to global change.
• Volkmann, T. H., Sengupta, A., Pangle, L., Dontsova, K. M., Troch, P. A., Meira, A., Neilson, J., Hunt, E., Chorover, J. D., Zeng, X., Van Haren, J. L., Barron-Gafford, G. A., Bugaj, A., Abramson, N., Sibayan, M., & Huxman, T. E. (2018). Controlled experiments of hillslope coevolution at the Biosphere 2 Landscape Evolution Observatory: Toward prediction of coupled hydrological, biogeochemical, and ecological change. In Hydrology of Artificial and Controlled Experiments. Rijeka, Croatia: InTech.
• Sengupta, A., Pangle, L., Volkmann, T., Dontsova, K. M., Troch, P. A., Meira, A. A., Neilson, J. W., Hunt, E., Chorover, J. D., Zeng, X., Van Haren, J. L., Barron-Gafford, G. A., Bugaj, A., Abramson, N., Sibayan, M., & Huxman, T. E. (2017). Advancing understanding of hydrological and biogeochemical interactions in evolving landscapes through controlled experimentation and monitoring at the Landscape Evolution Observatory. In Terrestrial Ecosystem Research Infrastructures: Challenges, New Developments and Perspectives(pp 83-118). CRC Press.
• Volkmann, T. H., Sengupta, A., Pangle, L. A., Dontsova, K. M., Barron-Gafford, G. A., Harman, C. J., Niu, G., Meredith, L., Abramson, N., Alves Meira Neto, A., Wang, Y., Adams, J. R., Breshears, D. D., Bugaj, A., Chorover, J. D., Cueva, A., DeLong, S. B., Durcik, M., Ferre, P. A., , Huxman, T. E., et al. (2017). Controlled Experiments of Hillslope Coevolution at the Biosphere 2 Landscape Evolution Observatory: Toward Prediction of Coupled Hydrological, Biogeochemical, and Ecological Changes. In Hydrology of Artificial and Controlled Experiments. Rijeka, Croatia: IN TECH d.o.o.
• Olivares, C. I., Abrell, L. M., Chorover, J. D., Simonich, M., Tanguay, R. L., Sierra-Alvarez, R., & Field, J. A. (2016). Identifying toxic biogransformation products of the insensitive munitions compound, 2,4-dinitroanisole (DNAN), using liquid chromatography coupled to quadrupole time-of-flight mass spectromety (LC-QToF-MS),. In Assessing Transformation Products of Chemicals by Non-Target and Suspect-Screening-Strategies and Workflows(pp 133-145). Chapter 9 Volume 1: Drewes, J. and Letzel (Eds). doi:10.1021/bk-2016-1241.ch009
• Olivares, C. I., Abrell, L. M., Chorover, J. D., Simonich, M., Tanguay, R. L., Sierra-Alvarez, R., & Field, J. A. (2016). Identifying toxic biogransformation products of the insensitive munitions compound,2,4-dinitroanisole (DNAN), using liquid chromatography coupled to quadrupole time-of-flight mass spectromety (LC-QToF-MS),. In Assessing Transformation Products of Chemicals by Non-Target and Suspect-Screening-Strategies and Workflows(pp 133-145). Chapter 9 Volume 1: Drewes, J. and Letzel (Eds). doi:10.1021/bk-2016-1241.ch009
• Sengupta, A., Pangle, L. A., Volkmann, T., Dontsova, K. M., Troch, P. A., Meira, A. A., Neilson, J. W., Hunt, E. A., Chorover, J. D., Zeng, X., van Haren, J., Barron-Gafford, G. A., Bugai, A., Abramson, N., Sibayan, M., & Huxman, T. E. (2016). Advancing understanding of hydrological and biogeochemical interactions in evolving landscapes through controlled experimentation and monitoring at the Landscape Evolution Observatory. In Terrestrial Ecosysem Research Infrastructrures: Challenges, New Developments and Perspectives(pp 83-118). Taylor and Francis Group, London UK.
• Sengupta, A., Pangle, L., Volkmann, T., Dontsova, K. M., Troch, P. A., Meira, A. A., Neilson, J. W., Hunt, E., Chorover, J. D., Zeng, X., Van Haren, J. L., Barron-Gafford, G. A., Bugaj, A., Abramson, N., Sibayan, M., & Huxman, T. E. (2016). Advancing understanding of hydrological and biogeochemical interactions in evolving landscapes through controlled experimentation and monitoring at the Landscape Evolution Observatory. In Terrestrial Ecosystem Research Infrastructures: Challenges, New developments and Perspectives(pp 179-193). CRC Press.
• Perdrial, J. A., Thompson, A., & Chorover, J. D. (2015). Soil geochemistry in the critical zone: Influence on atmosphere, surface- and groundwater composition.. In Developments in Earth Surface Processes Volume 19(pp 171-199). Chapter 6 Processes and Dynamics of the Critical Zone: Elsevier, The Netherlands.
• White, T. S., Brantley, S., Banwart, S., Chorover, J. D., Dietrich, W., Derry, L., Lohse, K., Anderson, S., Aufdenkampe, A., Bales, R., Kumar, P., Richter, D., & McDowell, W. (2015). The role of critical zone observatories in critical zone science.. In Developments in Earth Surface Processes Vol. 19(pp 15-78). Chapter 2 Processes and Dynamics of the Critical Zone: Elsevier, The Netherlands.
• Chorover, J. (2012). Impact of soil physicochemical and biological reactions on transport of nutrients and pollutants in the critical zone. In Handbook of Soil Science (2nd Edition)(pp 10.1-10.35). Academic Press, NY.
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  Editor(s): Huang, PM

Journals/Publications

• Moravec, B. G., Keifer, V., Root, R. A., White, A. M., Wang, Y., Olshansky, Y., McIntosh, J., & Chorover, J. (2021). Experimental weathering of a volcaniclastic critical zone profile: Key role of colloidal constituents in aqueous geochemical response. Chemical Geology, 559, 119886.
• Niu, X., Field, J. A., Paniego, R., Pepel, R. D., Chorover, J., Abrell, L., & Sierra-Alvarez, R. (2021). Bioconcentration potential and microbial toxicity of onium cations in photoacid generators. Environmental Science and Pollution Research, 28(7), 8915--8921.
• Wlostowski, A. N., Molotch, N., Anderson, S. P., Brantley, S. L., Chorover, J., Dralle, D., Kumar, P., Li, L. i., Lohse, K. A., Mallard, J. M., & others, . (2021). Signatures of Hydrologic Function Across the Critical Zone Observatory Network. Water Resources Research, e2019WR026635.
• Chorover, J. D. (2020). Life teems below the surface. EOS, 30-34. doi:10.1029
• Dwivedi, R., Eastoe, C., Knowles, J. F., Wright, W. E., Hamann, L., Minor, R., Mitra, B., Meixner, T., McIntosh, J., Ty, F., & others, . (2020). Vegetation source water identification using isotopic and hydrometric observations from a subhumid mountain catchment. Ecohydrology, 13(1), e2167.
• Dwivedi, R., Knowles, J. F., Eastoe, C., Minor, R., Abramson, N., Mitra, B., Wright, W. E., McIntosh, J., Meixner, T., Ferre, P. A., & others, . (2020). Ubiquitous fractal scaling and filtering behavior of hydrologic fluxes and storages from a mountain headwater catchment. Water, 12(2), 613.
• Fairbanks, D., Shepard, C., Murphy, M., Rasmussen, C., Chorover, J., Rich, V., & Gallery, R. (2020). Depth and topographic controls on microbial activity in a recently burned sub-alpine catchment. Soil Biology and Biochemistry, 107844.
• Hammond, C. M., Root, R. A., Maier, R. M., & Chorover, J. (2020). Arsenic and iron speciation and mobilization during phytostabilization of pyritic mine tailings. Geochimica et Cosmochimica Acta, 286, 306--323.
• Leone, J. D., Holbrook, W. S., Riebe, C. S., Chorover, J., Ferr\'e, T. P., Carr, B. J., & Callahan, R. P. (2020). Strong slope-aspect control of regolith thickness by bedrock foliation. Earth Surface Processes and Landforms, 45(12), 2998--3010.
• Moravec, B. G., White, A. M., Root, R. A., Sanchez, A., Olshansky, Y., Paras, B. K., Carr, B., McIntosh, J., Pelletier, J. D., Rasmussen, C., & others, . (2020). Resolving deep critical zone architecture in complex volcanic terrain. Journal of Geophysical Research: Earth Surface, 125(1), e2019JF005189.
• Reinoso-Maset, E., Perdrial, N., Steefel, C. I., Um, W., Chorover, J., & O’Day, P. A. (2020). Dissolved Carbonate and pH Control the Dissolution of Uranyl Phosphate Minerals in Flow-Through Porous Media. Environmental science \& technology, 54(10), 6031--6042.
• Angst, G., Mueller, K. E., Eissenstat, D. M., Trumbore, S., Freeman, K. H., Hobbie, S. E., Chorover, J. D., Oleksyn, K., Reich, P. B., & Mueller, C. W. (2019). Soil organic carbon stability in forests: Distinct effects of tree species identity and traits. Global Change Biol, 25, 1529-1546. doi:10.1111/gcb.14548
• Chorover, J. D., Reinhard, C. T., Maier, R. M., Li, K., Roldán-Nicolau, E. C., Castrejón-Martinez, R., Palacios-Menendez, M. A., Vaquera-Ibarra, M. O., Galey, M., Gaddis, E. E., Munoz, E. N., Sandhaus, S., Amistadi, M. K., Domanik, K., Hunt, E., Presler, J., Dontsova, K. M., Burghelea, C., & Zaharescu, D. (2019). From rock to life. A mass balance analysis of oxidative biological weathering and biosignature formation. Scientific Reports, 9, 15006. doi:10.1038/s41598-019-51274-x
• Dinali, G. S., Root, R. A., Amistadi, M. K., Lopes, G., Chorover, J. D., & Guilherme, L. G. (2019). Rare earth elements (REY) sorption on soils of contrasting mineralogy and texture. Environ. Int, 128, 279-291. doi:DOI: 10.1016/j.envint.2019.04.022
• Dwivedi, R., Meixner, T., Mcintosh, J. C., Ferre, P. A., Eastoe, C. J., Niu, G., Minor, R. L., Barron-Gafford, G. A., & Chorover, J. D. (2019). Hydrologic functioning of the deep Critical Zone and contributions to streamflow in a high elevation catchment: testing of multiple conceptual models. Hydrological Processes. doi:10.1002/hyp.13363
• Fang, Q., Hong, H. L., Algeo, T. J., Huang, X. Y., Sun, A., Churchman, G. J., Chorover, J. D., Chen, S. L., & Liu, Y. (2019). Microtopography-mediated hydrologic environment controls elemental migration and mineral weathering in subalpine surface soils of subtropical monsoonal China. Geoderma, 344, 82-98. doi:10.1016/j.geoderma.2019.03.008
• Fang, Q., Hong, H. L., Furnes, H., Chorover, J. D., Luo, Q., Zhao, L. L., & Algeo, T. J. (2019). Surficial weathering of kaolin regolith in a subtropical climate: Implications for supergene pedogenesis and bedrock argillization. Surficial weathering of kaolin regolith in a subtropical climate: Implications for supergene pedogenesis and bedrock argillization, 337, 225-237. doi:10.1016/j.geoderma.2018.09.020
• Honeker, L. K., Gullo, C. F., Neilson, J. W., Chorover, J. D., & Maier, R. M. (2019). Effect of re-acidification on Buffalo Grass rhizosphere and bulk microbial communities during phytostabilization of metalliferous mine tailings. Front. Microbiol, 10(1209). doi:10.3389/fmicb.2019.01209
• Hottenstein, J. D., Neilson, J. W., Gil-Loaiza, J., Root, R. A., White, S. A., Chorover, J. D., & Maier, R. M. (2019). Soil microbiome dynamics during pyritic mine tailing phytostabilization: Understanding microbial bioindicators of soil acidification. Front Microbiol, 10(1211). doi:10.3389/fmicb.2019.01211
• Maier, R. M., Troch, P. A., Chorover, J. D., Dontsova, K. M., Hunt, E., Tatarin, T., Neilson, J. W., Wang, Y., Meira Neto, A. A., Stegen, J., & Sendupta, A. (2019). Assessing Microbial Community Patterns During Incipient Soil Formation From Basalt. Journal of Geophysical Research: Biogeosciences, 124, 941–958. doi:10.1029/2017jg004315
• Sengupta, A., Stegen, J. C., Meira, N., Wang, Y., Neilson, J. W., Tatarin, T., Hunt, E., Dontsova, K., Chorover, J., Troch, P. A., & others, . (2019). Assessing microbial community patterns during incipient soil formation from basalt. Journal of Geophysical Research: Biogeosciences, 124(4), 941--958.
• Burghelea, C. I., Dontsova, K., Zaharescu, D. G., Maier, R. M., Huxman, T., Amistadi, M. K., Hunt, E., & Chorover, J. D. (2018). Trace element mobilization during incipient bioweathering of four rock types. Geochim. Cosmochim. Acta, 234, 98-114. doi:10.1016/j.gca.2018.05.011
• Chorover, J. D., Hunt, E., Amistadi, M. K., Huxman, T. E., Maier, R. M., Dontsova, K. M., Zaharescu, D., & Burghelea, C. (2018). Trace element mobilization during incipient bioweathering of four rock types. Geochimica et Cosmochimica Acta, 234, 98-114. doi:https://doi.org/10.1016/j.gca.2018.05.011
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  Lithogenic trace element (TE) patterns of distribution, fate, and behavior in soils are influenced by plants and microorganisms. Our controlled mesocosm experiments quantified how incipient weathering of mineral-bound TEs (Be, V, Sr, Ba, Cr, Co, Ni, Mo, Cu, Zn, As, Se, Ag, Cd, Sn, Sb, Tl, and Pb) varies across four porous mineral substrates (basalt, rhyolite, granite, and schist), in the presence of buffalo grass (Bouteloua dactyloides), associated bacteria, and arbuscular mycorrhizal fungi (AM), a common plant symbiont. Particular focus was given to the net transfer of elements between the solid and solution phases, including chemical denudation (loss of element from the rock to the solution), plant TE uptake, and total mobilization (sum of denudation loss and uptake into plant biomass). Results revealed differences in TE denudation among rocks, basalt having the highest loss and schist the lowest. TE leaching in solution was time-dependent and it was likely influenced by variations in pH and DOC that were rock- and treatment-specific. The element with the highest rock-normalized release to the solution and highest enrichment in plant biomass was Mo across all rocks. Plants decreased denudation loss compared to abiotic controls for a large number of TEs in all substrates due to plant uptake, but for some elements increase in weathering due to plant activity resulted in increased denudation. Differences in TE patterns of behavior could be related to their Goldschmidt groups. Plant uptake was controlled by TE availability in solution, as well as plant physiological requirements. Plants and associated microbiota significantly enhanced mobilization for the majority of TEs across all rocks. Mycorrhiza significantly increased above-ground plant biomass production in rhyolite and concentrations in plant tissues for a high number of TEs in basalt. TE uptake into biomass was positively correlated with percent mycorrhizal infection, particularly in basalt and rhyolite. Mycorrhizal fungi also influenced TE denudation, rock-water fractionation, and total mobilization according to the rock type. Mycorrhizal activity was associated with a significant decrease in pH and increase in DOC fluxes in schist, supporting the idea that fungi enhance production of root exudates especially in substrates that are difficult to weather. Our results highlight the importance of incipient weathering at the plant-rock interface for patterns of TE cycling. They also indicate the importance of mycorrhiza in mineral dissolution, TE denudation, plant element uptake, and biomass growth.
• Chorover, J. D., Mcintosh, J. C., Moravec, B., White, A., & Olshansky, Y. (2018). Subsurface pore water contributions to stream concentration-discharge relations across a snowmelt hydrograph. Frontiers in Earth Science, 09 November 2018. doi:doi:org/10.3389/feart.2018.00181
• Hammond, C. M., Root, R. A., Maier, R. A., & Chorover, J. D. (2018). Mechanisms of arsenic sequestration by Prosopis juliflora during the phytostabilization of metalliferous mine tailings. Environ. Sci. Technol., 52, 1156-1164.
• Huskey, D. A., Curlango-Rivera, G., Root, R. A., Wen, F. S., Amistadi, M. K., Chorover, J. D., & Hawes, M. C. (2018). Trapping of lead (Pb) by corn and pea root border cells. Plant adn Soil, 430, 205-217. doi:10.1007/s11104-018-3716-4
• Khatiwada, R., Abrell, L., Li, G. B., Root, R. A., Sierra-Alvarez, R., Field, J. A., & Chorover, J. D. (2018). Adsorption and oxidation of 3-nitro-1,2,4-triazole-5-one (NTO) and its transformation product (3-amino-1,2,4-triazole-5-one, ATO) at ferrihydrite and birnessite surfaces. Environ. Pollut., 240, 200-208. doi:10.1016/j.envpol.2018.04.034
• Khatiwada, R., Olivares, C., Abrell, L., Root, R. A., Sierra-Alvarez, R., Field, J. A., & Chorover, J. D. (2018). Oxidation of reduced daughter products from 2,4-dinitroanisole (DNAN) by Mn(IV) and Fe(III) oxides. Chemosphere, 201, 790-798. doi:10.1016/j.chemosphere.2018.03.020
• Khatiwada, R., Root, R. A., Abrell, L., Sierra-Alvarez, R., Field, J. A., & Chorover, J. D. (2018). Abiotic reducton of insensitive munition compounds by sulfate green rust. Environ. Chem., 15, 259-266. doi:10.1071/EN17221
• Madeira, C. L., Field, J. A., Simonich, M. T., Tanguay, R. L., Chorover, J. D., & Sierra-Alvarez, R. (2018). Ecotoxicity of the insensitive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO) and its reduced metabolite 3-amino-1,2,4-triazol-5-one (ATO). J. Haz. Mat., 343, 340-346.
• Olshansky, Y., Root, R. A., & Chorover, J. D. (2018). Wet-dry cycles impact DOM retention in subsurface soils. Biogeosciences, 15, 821-832.
• Olshansky, Y., White, A. M., Moravec, B. G., & Chorover, J. D. (2018). Subsurface pore water contributions to stream concentration-discharge relations across a snowmelt hydrograph.. Front. Earth Sci, 6(UNSP 181). doi:10.3389/feart.2018.00181
• Perdrial, J., Brooks, P. D., Swetnam, T., Lohse, K. A., Rasmussen, C., Litvak, M., Harpold, A. A., Zapata-Rios, X., Broxton, P., Mitra, B., Meixner, T., Condon, K., Huckle, D., Stielstra, C., Vazquez-Ortega, A., Lybrand, R., Holleran, M., Orem, C., Pelletier, J., & Chorover, J. D. (2018). Treatment impacts on temporal microbial community dynamics during phytostabilization of acid-generating mine tailings in semiarid regions. Sci. Tot. Environ., 618, 357-368. doi:10.1016/j.scitotenv.2017.00.010
• Perdrial, N., Vazquez-Ortega, A., Wang, G., Kanematsu, M., Mueller, K. T., Um, W., Steefel, C. I., O'Day, P. A., & Chorover, J. D. (2018). Uranium speciation in acid waste-weathered sediments: The role of aging and phosphate amendments. Appl. Geochem, 89, 109-120. doi:doi.org/10.1016/j.apgeochem.2017.12.001
• Sanchez-Canete, E. P., Barron-Gafford, G. A., & Chorover, J. D. (2018). A considerable fraction of soil-respired Co2 is not emitted directly to the atmosphere. Sci. Rep., 8(13518). doi:10.1038/s41598-018-29803-x
• Shepard, C., Schaap, M. G., Chorover, J. D., & Rasmussen, C. (2018). Understanding critical zone evolution through predicting the three-dimensional soil chemical properties of a small forested catchment.. Soil. Sci. Soc. Am. J., 82, 1538-1550. doi:10.2136/sssaj2018.03.0119
• van Haren, J., Dontsova, K., Barron-Gafford, G. A., Troch, P. A., Chorover, J. D., DeLong, S. B., Breshears, D. D., Huxman, T. E., Pelletier, J. D., Saleska, S. R., Zeng, X., & Ruiz, J. (2017). CO2 diffusion into pore spaces limits weathering rate of an experimental basalt landscape. Geology, 45, 203-206. doi:10.1130/G38569.1
• Brantley, S. L., McDowell, W. H., Dietrich, W. E., White, T. S., Kumar, P., Anderson, S. P., Chorover, J. D., Lohse, K. A., Bales, R. C., Richter, D. D., Grant, G., & Gaillardet, J. (2017). Designing a network of critical zone observatories to explore the living skin of the terrestrial Earth. Earth Surface Dynamics, 5, 841-860. doi:10.5194/esurf-5-842-2017
• Chorover, J. D. (2017). Geochemical evolution of the critical zone across variable time scales informs concentration-discharge relationships: Jemez River Basin Critical Zone Observatory. Water Resour. Res., 53, 4169-4196.
• Chorover, J. D. (2017). Uranium release from acidic weathered sediments: Single-pass flow-through and column experiments. Environ. Sci. Technol., 51, 10111-11019.
• Chorover, J. D., Derry, L. A., & McDowell, W. H. (2017). Concentration-discharge relations in the critical zone: Implications for resolving critical zone structure, function and evolution.. Water Resour. Res.. doi:doi.org/10/1002/2017WR021111
• Dwivedi, R., Meixner, T., Mcintosh, J. C., Ferre, P. A., Eastoe, C. J., Niu, G., Minor, R. L., Barron-Gafford, G. A., & Chorover, J. D. (2020). Hydrologic functioning of the deep Critical Zone and contributions to streamflow in a high elevation catchment: testing of multiple conceptual models. Hydrological Processes. doi:10.1002/hyp.13363
• Honeker, L. K., Neilson, J. W., Root, R. A., Gil-Loaiza, J., Chorover, J. D., & Maier, R. M. (2017). Bacterial rhizoplane colonization patterns of Buchloe dactyloides growing in metalliferous mine tailings reflect plant status and biogeochemical conditions. Microbial Ecology, 74, 853-867. doi:10.1007/s00248-017-0998-7
• Hunt, E., Huxman, T. E., Maier, R. M., Chorover, J. D., Dontsova, K. M., Burghelea, C., & Zaharescu􀀃, G. D. (2017). Ecosystem Composition Controls the Fate of Rare Earth Elements during Incipient Soil Genesis. Scientific Reports, 7, 43208. doi:10.1038/srep43208
• Madeira, C. L., Speet, S. A., Nieto, C. A., Abrell, L., Chorover, J. D., Sierra-Alvarez, R., & Field, J. A. (2017). Sequential anaerobic-aerobic biodegradation of emerging insensitive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO).. Chemosphere, 167, 478-484.
• Olivares, C. I., Madeira, C. L., Sierra-Alvarez, R., Kadoya, W., Abrell, L., Chorover, J. D., & Field, J. A. (2017). Environmental fate of C-14 radiolabeled 2,4-dinitroanisole in soil microcosms.. Environ. Sci. Technol., 51, 13327-13334.
• Reinoso-Maset, E., Steefel, C. I., Um, W., Chorover, J. D., & O'Day, P. A. (2017). Rates and mechanisms of uranyl oxyhydroxide mineral dissolution. Geochim. Cosmochim. Acta, 207, 298-321.
• Ruiz, J., Pelletier, J. D., Zeng, X., Breshears, D. D., Huxman, T. E., DeLong, S., Saleska, S. R., Chorover, J. D., Troch, P. A., Barron-Gafford, G. A., Dontsova, K. M., & Van Haren, J. L. (2017). CO2 diffusion into pore spaces limits weathering rate of an experimental basalt landscape. Geology, 45(3), 203-206. doi:10.1130/G38569.1
• Van Haren, J. L., Dontsova, K. M., Barron-Gafford, G. A., Troch, P. A., Chorover, J. D., Saleska, S. R., DeLong, S., Huxman, T. E., Breshears, D. D., Zeng, X., Pelletier, J. D., & Ruiz, J. (2017). CO2 diffusion into pore spaces limits weathering rate of an experimental basalt landscape. Geology.
• Zaharescu, D. G., Burghelea, C. I., Dontsova, K., Presler, J. K., Maier, R. M., Huxman, T., Domanik, K. J., Hunt, E. A., Amistadi, M. K., Gaddis, E. E., Palacios-Menendez, M. A., Vaquera-Ibarra, M. O., & Chorover, J. D. (2017). Ecosystem composition controls the fate of rare earth elements during incipient soil genesis. Scientific Reports, 7, 43208. doi:10.1038/srep432082
• Zaharescu􀀃, G. D., Burghelea, C., Dontsova, K. M., Chorover, J. D., Maier, R. M., Huxman, T. E., & Hunt, E. (2017). Ecosystem Composition Controls the Fate of Rare Earth Elements during Incipient Soil Genesis. Nature Scientific Reports, 7, 43208. doi:10.1038/srep43208
• Chorover, J. D., Troch, P. A., Ruiz, J., Root, R., Dontsova, K. M., & Pohlmann, M. (2016). Pore water chemistry reveals gradients in mineral transformation across a model basaltic hillslope. Geochemistry, Geophysics, Geosystems, 17(6), 2054–2069.
• Field, J. P., Breshears, D. D., Law, D. J., Lopez-Hoffman, L., Brooks, P. D., Chorover, J. D., Pelletier, J. D., & Villegas, J. C. (2016). Broadening ecosystem services through inclusion of a geoscience perspective. EOS.
• Field, J. P., Field, J. P., Breshears, D. D., Breshears, D. D., Law, D. J., Law, D. J., Villegas, J. C., Lopez-Hoffman, L., Brooks, P. D., Lopez-Hoffman, L., Brooks, P. D., Chorover, J. D., Pelletier, J. D., Chorover, J., Villegas, J. C., & Pelletier, J. D. (2016). Understanding ecosystem services from a geosciences perspective. Eos, 97. doi:10.1029/2016EO043591
• Gil-Loaiza, J., White, S. A., Root, R., Solis-Dominguez, F. A., Hammond, C. M., Chorover, J. D., & Maier, R. M. (2016). Phytostabillization of mine tailings using compost-assisted direct planting: Translating greenhouse results ot the field. Sci Tot Environ, 565, 451-461.
• Honeker, L. K., Root, R., Chorover, J. D., & Maier, R. M. (2016). Resolving colocalization of bacteria and metal(loids) on plant root surfaces by combining fluorescence in situ hybridization (FISH) with multiple-energy micro-focused X-ray fluorescence. J. Microbiol. Meth., 131, 23-33.
• Huckle, D., Ma, L., Mcintosh, J. C., Vazquez-Ortega, A., Rasmussen, C., & Chorover, J. D. (2016). U-series isotopic signatures of soils and headwater streams in a semi-arid complex volcanic terrain. Chemical Geology, 445, 68-83.
• Huckle, D., Ma, L., Mcintosh, J. C., Vazquez-Ortega, A., Rasmussen, C., & Chorover, J. D. (2016). U-series osotopic signatures of soils and headwater streams in a semi-arid complex volcanic terrain. Chem Geol., 445, 68-83.
• Madeira, C. L., Speet, S. A., Nieto, C. A., Abrell, L. M., Chorover, J. D., Sierra-Alvarez, R., & Field, J. A. (2016). Sequential anaerobic-aerobic biodegradatin of emerging insenstive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO). Chemospher, 167, 478-484.
• Madeira, C. L., Speet, S. A., Nieto, C. A., Abrell, L. M., Chorover, J. D., Sierra-Alvarez, R., & Field, J. A. (2017). Sequential anaerobic-aerobic biodegradatin of emerging insenstive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO). Chemosphere, 167, 478-484.
• Mueller, K. E., Eisenhauer, N., Reich, P. B., Hobbie, S. E., Chadwick, O. A., Chorover, J. D., Dobies, T., Hale, C. M., Jagodzinski, A. M., Kalucka, I., Kasprowicz, M., Kielszewska-Rokicka, B., Modrzynski, J., Rozen, A., Skorupski, M., Sozczyck, L., Stasinska, M., Trocha, L. K., Weiner, J., , Wierzbicka, A., et al. (2016). Light, earthworms, and soil resources as predictors of diversity of 10 soil invertebrate groups across monocultures of 14 tree species. Soil Biol. Biochem., 92, 184-198. doi:10.1016/j.soilbio.2015.10.010
• Olivares, C. I., Abrell, L. M., Khatiwada, R., Chorover, J. D., Sierra-Alvarez, R., & Field, J. A. (2016). (Bio)transformation of 2,4-dinitroanisole (DNAN) in soils. J Haz Mater, 304, 214-221.
• Olivares, C. I., Sierra-Alvarez, R., Abrell, L. M., Chorover, J. D., Simonich, M., Tanguay, R. L., & Field, J. A. (2016). Zebrafish embryo toxicity of anaerobic biotransformation products from the insensitive munitions compout 2,4-dintroanisole. Environ. Toxicol. Chem., 35, 2774-2781.
• Olivares, C. I., Sierra-Alvarez, R., Alvarez-Nieto, C., Abrell, L. M., Chorover, J. D., & Field, J. A. (2016). Microbial toxicity and characterization of DNAN (bio)transformation product mixtures. Chemosphere, 154, 499-506.
• Pohlmann, M., Dontsova, K. M., Root, R., Ruiz, J., Troch, P. A., & Chorover, J. D. (2016). Pore water chemistry reveals gradients in mineral transformation across a model basaltic hillslope. Geochemistry, Geophysics, Geosystems, 17, 2054-2069. doi:10.1002/2016GC006270
• Rasmussen, C., Troch, P. A., Pelletier, J. D., Swetnam, T. W., & Chorover, J. D. (2015). Quantifying topographic and vegetation effects on the trnasfer of energy and mass to a critical zone. Vadose Zone Journal.
• Rodriguez-Freire, L., Moore, S. E., Sierra-Alvarez, R., Root, R. A., Chorover, J. D., & Field, J. A. (2016). Arsenic remediation by formation of arsenic sulfide minerals in a continous anaerobic bioreactor. Biotechnol. Bioengineer., 113, 522-530.
• Sagarin, R., Sagarin, R., Troch, P. A., Troch, P. A., Adams, J., Adams, J., Brusca, R., Brusca, R., Blanchette, C., Blanchette, C., Chorover, J. D., Chorover, J. D., Cole, J. E., Cole, J. E., Micheli, F., Micheli, F., Munguia-Vega, A., Munguia-Vega, A., Rochman, C., , Rochman, C., et al. (2016). Between Control and Complexity: Opportunities and Challenges for Marine Mesocosms. Frontiers in Ecology and the Environment, 14, 389-396.
• Sengupta, A., Wang, Y., Meira, A. A., Matos, K., Dontsova, K. M., Root, R., Neilson, J. W., Chorover, J. D., Maier, R. M., & Troch, P. A. (2016). Soil lysimeter excavation for coupled hydrological, geochemical, and microbiological investigations. JoVE, 115(e54536). doi:10.3791/54536
• Troch, P. A., Maier, R. M., Chorover, J. D., Neilson, J. W., Root, R., Dontsova, K. M., Matos, K., Meira, A. A., Wang, Y., & Sengupta, A. (2016). Soil Lysimeter Excavation for Coupled Hydrological, Geochemical, and Microbiological Investigations. JoVE, e54536. doi:10.3791/54536
• Trostle, K. D., Runyon, J. R., Pohlmann, M., Redfield, S. E., Pelletier, J. D., Mcintosh, J. C., & Chorover, J. D. (2016). Colloids and organic matter complexation control trace metal concentration-dsicharge relationships in Marshall Gulch stream waters. Wat. Resour. Res, 52, 7931-7944.
• Trostle, K. D., Runyon, J. R., Pohlmann, M., Redfield, S. E., Pelletier, J. D., Mcintosh, J. C., & Chorover, J. D. (2016). Colloids and organic matter complexation control trace metal concentration-dsicharge relationships in Marshall Gulch stream waters. Water Resources Research, 52, 7931-7944.
• Vazquez-Ortega, A., Huckle, D., Perdrial, J., Amistadi, M. K., Durcik, M., Rasmussen, C., Mcintosh, J. C., & Chorover, J. D. (2016). Solid-phase redistribution of rare earth elements in hillslope pedons subjected to different hydrologic fluxes. Chemical Geology, 426, 1-18.
• Vázquez-Ortega, A., Huckle, D., Perdrial, J., Amistadi, M. K., Durcik, M., Rasmussen, C., Mcintosh, J. C., & Chorover, J. D. (2016). Solid-phase redistribution of rare earth elements in hillslope pedons subjected to different hydrologic fluxes. Chemical Geology, 426, 1-18. doi:10.1016/j.chemgeo.2016.01.001
• Zachara, J., Brantley, S. L., Chorover, J. D., Ewing, R., Kerisit, S., Liu, C., Perfect, E., Rother, G., & Stack, A. G. (2016). Internal domains of natural porous media revealed: Critical locations for transport, storage and chemical reaction. Eviron. Sci. Technol., 50, 2811-2829.
• Brooks, P. D., Chorover, J. D., Fan, Y., Godsey, S. E., Maxwell, R. M., McNamara, J. P., & Tague, C. (2015). Hydrological partitioning in the critical zone: Recent advances and opportunities for developing ransferable understanding of water cycle dynamics.. Water Resour. Res., 51, 6973-6987. doi:10.1002/2015WR017039
• Burghelea, C., Zaharescu, G. D., Dontsova, K. M., Maier, R. M., Huxman, T., & Chorover, J. D. (2015). Mineral nutrient mobilization by plants from rock: Influence of rock type and arbuscular mycorrhiza. Biogeochemistry, 124(1-3), 187-203. doi:10.1007/s10533-015-0092-5
• Burghelea, C., Zaharescu, G. D., Dontsova, K. M., Maier, R. M., Huxman, T., & Chorover, J. D. (2015). Mineral nutrient mobilization by plants from rock: Influence of rock type and arbuscular mycorrhiza. Biogeochemistry.
• Chorover, J. D. (2015). Forward to the Research Front on "Mineral-Organic Interactions in Aqueous Systems". Environ. Chem., 12, 1-2.
• Field, J. P., Breshears, D. D., Law, D. J., Villegas, j. C., Lopez Hoffman, L. -., Brooks, P. D., Chorover, J., Barron-Gafford, G. A., Gallery, R. E., Litvak, M. E., Lybrand, R., Mcintosh, J. C., Meixner, T. -., Niu, Y. -., Papuga, S. A., Pelletier, J. D., Rasmussen, C. -., & Troch, P. A. (2015). Critical zone services: Expanding context, constraints, and curency beyond ecosystem services.. Vadose Zone Journal, 1-7.
• Kzmarzick, M. J., Khatiwada, J. R., Olivares, C. I., Abrell, L., Sierra Alvarez, M. R., Chorover, J. D., & Field, J. A. (2015). Biotransformation and degradation of the insensitive munitions compound, 3-nitro-1,2,4-triazol-5-one, by soil bacterial communities.. Environ. Sci. Technol., 49, 5681-5688.
• Linker, B. R., Khatiwada, R., Perdrial, N., Abrell, L., Sierra-Alvarez, R., Field, J. A., & Chorover, J. D. (2015). Adsoprtion of novel insensitive minutions compounds at clay mineral and metal oxide surfaces. Environ. Chem., 12, 74-84. doi:http://dx.doi.org/10/1071/EN14065
• Mueller, K. E., Hobbie, S. E., Chorover, J. D., Reich, P. B., Chadwick, O. A., Eisenhauer, N., Castellano, M. J., Dobies, T., Eissenstat, D., Hale, C. M., Jadodzinski, A. J., Kalucka, I., Kieliszweska-Rokicka, B., Modrzynski, J., Rozen, A., Skorupski, M., Sobczyk, L., Stasinska, M., Trocha, K. L., , Weiner, J., et al. (2015). Effects of litter traits, soil biota, and soil chemistry, and stand characteristics on soild C stocks at a common garden with 14 tree species. Biogeochem..
• Nelson, K. N., Neilson, J. A., Root, R. A., Chorover, J. D., & Maier, R. M. (2015). Abundance and activity of 16S rRNA, AmoA and NifH bacterial genes during assisted phytostabilization of mine tailings. Int. J. phytoremed., 17, 493-502.
• Pangle, L. A., Pangle, L. A., Pangle, L. A., Delong, S. B., Delong, S. B., Delong, S. B., Abramson, N., Abramson, N., Abramson, N., Adams, J., Adams, J., Adams, J., Barron-Gafford, G. A., Barron-Gafford, G. A., Barron-Gafford, G. A., Breshears, D. D., Breshears, D. D., Breshears, D. D., Brooks, P. D., , Brooks, P. D., et al. (2015). The Landscape Evolution Observatory: A large-scale controllable infrastructure to study Earth-surface processes.. Geomorphology, 244, 190-203.
• Pangle, L., DeLong, S., Abramson, N., Adams, J., Barron-Gafford, G. A., Breshears, D. D., Brooks, P. D., Chorover, J. D., Dietrich, W. E., Dontsova, K. M., Durcik, M., Espeleta, J., Ferre, P. A., Ferriere, R. H., Henderson, W., Hunt, E., Huxman, T. E., Millar, D., Murphy, B., , Niu, Y., et al. (2015). The Landscape Evolution Observatory: A large-scale controllable infrastructure to study coupled Earth-surface processes. Geomorphology, 244, 190-203.
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• Pangle, L., DeLong, S., Abramson, N., Adams, J., Barron-Gafford, G. A., Breshears, D. D., Brooks, P. D., Chorover, J. D., Dietrich, W. E., Dontsova, K. M., Durcik, M., Espeleta, J., Ferre, P. A., Ferriere, R. H., Henderson, W., Hunt, E., Huxman, T. E., Millar, D., Murphy, B., , Niu, Y., et al. (2015). The Landscape Evolution Observatory: A large-scale controllable infrastructure to study coupled Earth-surface processes. Geomorphology.
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• Perdrial, N., Thompson, A., LaSharr, K., Amistadi, M. K., & Chorover, J. D. (2015). Quantifying particulate and colloidal relsease of radionuclides in waste-weathered Hanford sediments. J. Environ. Qual..
• Rasmussen, C., Pelletier, J. D., Troch, P. A., Swetnam, T. W., & Chorover, J. D. (2015). Quantifying topographic and vegetation effects on the trnasfer of energy and mass to a critical zone. Vadose Zone Journal.
• Root, R. A., Hayes, S. M., Hammond, C., Maier, R. M., & Chorover, J. D. (2015). Toxic metal(loid) speciation during weatherin gof iron sulfide mine tailings under semi-arid climate. Appl. Geochem..
• Stielstra, C. M., Lohse, K. A., Chorover, J. D., McIntosh, J. C., Barron-Gafford, G. A., Perdrial, J. N., Litvak, M., Barnhard, H. R., & Brooks, P. D. (2015). Climatic and landscape influences on soil moisture are primary determinants of soil carbon fluxes in seasonally snow-covered forest ecosystems.. Biogeochem., 123, 447-465.
• Stielstra, C. M., Lohse, K., Chorover, J. D., Mcintosh, J. C., Barron-Gafford, G. A., Perdrial, J. N., Litvak, M., Barnard, H., & Brooks, P. (2015). Climatic, landscape, and edaphic controls on soil carbon efflux in seasonally snow covered forest ecosystems. Biogeochemistry.
• Van Haren, J. L., Dontsova, K. M., Barron-Gafford, G. A., Troch, P. A., Chorover, J. D., Saleska, S. R., DeLong, S., Huxman, T. E., Breshears, D. D., Zeng, X., Pelletier, J. D., & Ruiz, J. (2016). CO2 diffusion into pore spaces limits weathering rate of an experimental basalt landscape. Geology.
• Vazquez-Ortega, A., Perdrial, J., Harpold, A., Zapata-Rios, X., Rasmussen, C., McIntosh, J., Schaap, M. G., Pelletier, J. D., Brooks, P. D., Amistadi, M. K., & Chorover, J. D. (2015). Rare earth elements as reactive tracers of biogeochemical weathering in forested rhyolitic terrain. Chem. Geol., 391, 19-32.
• Villegas, J. C., Pelletier, J. D., Chorover, J. D., Brooks, P. D., Lopez-Hoffman, L., Law, D. J., Breshears, D. D., & Field, J. P. (2015). Understanding of ecosystem services from a geosciences perspective. EOS, 97. doi:doi:10.1029/2016EO043591.
• Zapata-Rios, X., Mcintosh, J. C., Rademacher, L., Troch, P. A., Brooks, P. D., Rasmussen, C., & Chorover, J. D. (2015). Climatic and landscape controls on water transit times and silicate mineral weathering in the Critical Zone. Water Resources Research.
• Abrell, L. M., Mash, E. A., Field, J. A., Chorover, J. D., Sierra Alvarez, M. R., & Bhumasamudram, J. (2014). Synthesis of 13C and 15N labeled 2,4-dinitroanisole. Journal of Labelled Compounds and Radiopharmaceuticals.
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  Abstract Syntheses of [13C6]-2,4-dinitroanisole (ring-13C6) from [13C6]-anisole (ring-13C6) and[15N2]-2,4-dinitroanisole from anisole using in situ generated acetyl nitrate and [15N]-acetylnitrate, respectively, are described. Treatment of [13C6]-anisole (ring-13C6) with acetyl nitrategenerated in 100% HNO3 gave [13C6]-2,4-dinitroanisole (ring-13C6) in 83% yield. Treatment ofanisole with [15N]-acetyl nitrate generated in 10N [15N]-HNO3 gave [15N2]-2,4-dinitroanisole in44% yield after two cycles of nitration. Byproducts in the latter reaction included [15N]-2-nitroanisole and [15N]-4-nitroanisole.
• Chorover, J. D., Dontsova, K., Zaharescu, D., Henderson, W., Verghese, S., Perdrial, N., & Hunt, E. (2014). Impact of organic carbon on weathering and chemical denudation of granular basalt. Geochim. Cosmochim. Acta, 139, 508-526.
• Chorover, J. D., Gavaert, A., Tueling, A. J., Uijlenhoet, R., DeLong, S. B., Huxman, T. E., Pangle, L., Brashears, D. D., Pelletier, J. D., Saleska, S. R., Zeng, X., & Troch, P. A. (2014). Hillslope-scale experiment demonstrates the role of convergence during two-step saturation. Hydrol. Earth Syst. Sci., 18, 1-12.
• Chorover, J. D., Kanematsu, M., Perdrial, N., Um, W., & O'Day, P. A. (2014). Influence of Phosphate and Silica on U(VI) Precipitation from Acidic and Neutralized Wastewaters. Environmental Science Technology, 48, 6097-6106.
• Chorover, J. D., Maier, R. M., Root, R. A., Hayes, S. M., & Perdrial, N. (2014). Surficial weathering of iron sulfide mine tailings under semi-arid climate. Geochim. Cosmochim. Acta, 141, 240-257.
• Chorover, J. D., Menka, N., & Root, R. (2014). Bioaccessibility, release kinetics, and moelcular speciation of arsenic and lead in geo-dusts from the Iron King Mine Federal Superfund site in Humboldt, Arizona. Rev Environmental Health.
• Chorover, J. D., Perdrial, J., McIntosh, J., Harpold, A., Brooks, P. D., Zapata-Rios, X., Ray, J., Kanduc, T., Litvak, M., Troch, P. A., & Meixner, T. (2014). Stream water carbon controls in seasonally snow-covered mountain catchments: impact of inter-annual variability of water fluxes, catchment aspect and seasonal processes. Biogeochem, 118, 273-290.
• Chorover, J. D., Perdrial, J., Perdrial, N., Vazquez-Ortega, A., Porter, C., & Leedy, J. (2014). Experimental assessment of passive capillary wick sampler suitability for inorganic soil solution constituents. Soil Science Society of America Journal, 78, 486-495.
• Chorover, J. D., Perdrial, N., Thompson, A., O'Day, P. A., & Steefel, C. I. (2014). Mineral transformation controls speciation and pore-fluid transmission of contaminants in waste-weathered Hanfod sediments. Geochim. Cosmochim. Acta, 141, 487-507.
• Chorover, J. D., Rodriguez-Freire, L., Sierra Alvarez, M. R., Root, R., & Field, J. A. (2014). Biomineralization of arsenate to arsenic sulfides is greatly enhanced at mildly acidic conditions. Wat. Res., 66, 242-253.
• Chorover, J. D., Valentin-Vargas, A., Root, R. A., Neilson, J. W., & Maier, R. M. (2014). Environmental factors influencing the structural dynamics of soil microbial communities during assisted phytostabilization of acid-generating mine tailings: A mesocosm experiment.. Sci. Tot. Environ., 500, 314-324.
• Dontsova, K. M., Zaharescu, G. D., Henderson, W., Verghese, S., Perdrial, N., Hunt, E., & Chorover, J. D. (2014). Impact of organic carbon on weathering and chemical denudation of granular basalt. Geochimica et Cosmochimica Acta, 139, 508-526.
• Field, J. P., Breshears, D. D., Law, D. J., Villegas, J., Lopez Hoffman, L. -., Brooks, P. D., Chorover, J., Barron-Gafford, G. A., Gallery, R. E., Litvak, M. E., Lybrand, R., Mcintosh, J. C., Meixner, T. -., Niu, Y. -., Papuga, S. A., Pelletier, J. D., Rasmussen, C. -., & Troch, P. A. (2014). Critical Zone Services: Expanding Context, Constraints, and Currency beyond Ecosystem Services. Vadose Zone Journal.
• Niu, G., Pasetto, D., Scudeler, C., Paniconi, C., Putti, M., Troch, P. A., DeLong, S. B., Dontsova, K., Pangle, L., Breshears, D. D., Chorover, J., Huxman, T. E., Pelletier, J., Saleska, S. R., & Zeng, X. (2014). Incipient subsurface heterogeneity and its effect on overland flow generation – insight from a modeling study of the first experiment at the Biosphere 2 Landscape Evolution Observatory. Hydrology and Earth System Sciences.
• Niu, Y., Pasetto, D., Scudeler, C., Paniconi, C., Putti, M., Troch, P. A., DeLong, S., Dontsova, K. M., Pangle, L., Breshears, D. D., Chorover, J. D., Huxman, T. E., Pelletier, J. D., Saleska, S. R., & Zeng, X. (2014). Incipient subsurface heterogeneity and its effect on overland flow generation -- insight from a modeling study of the first experiment at the Biosphere 2 Landscape Evolution Observatory. Hydrol. Earth Syst. Sci., 18, 1873-1883.
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• Vazquez-Ortega, A., Hernandez-Ruiz, S., Amistadi, M. K., Rasmussen, C., & Chorover, J. (2014). Fractionation of Dissolved Organic Matter by (Oxy)Hydroxide-Coated Sands: Competitive Sorbate Displacement during Reactive Transport. Vadose Zone Journal, 13(7).
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  Sorptive retention of dissolved organic matter (DOM) at soil particle surfaces controls C flux through the critical zone. Prior studies have shown that pristine Al-and Fe-(oxy) hydroxide surfaces are especially reactive toward DOM sorptive stabilization. However, the impact of progressive and/or preexisting organic surface coatings on further surficial uptake and exchange during repeated DOM infusion episodes remains unclear. In this study, DOM solutions were extracted from organic horizons in grassland (G) and mixed conifer forest (F) vegetation types in the Jemez River Basin Critical Zone Observatory. Extracted DOM solutions were used to sequentially irrigate columns packed with either quartz sand (Qtz), Al-hydroxide-coated quartz sand (Al-Qtz), or Fe-hydroxide-coated quartz sand (Fe-Qtz). Use of distinct DOM sources enabled investigation of how sorption, fractionation, and exchange ensued during reactive transport through mineral media progressively coated with sorbate organic matter (SOM). During initial irrigation of fresh mineral media with G-DOM, the magnitude of DOM sorption (per unit sorbent mass) followed the trend: Al-Qtz >= Fe-Qtz > Qtz. Effluent solutions showed diminished molar absorptivity and humification index (HIX) values, indicating preferential uptake of high-molar-mass aromatic constituents. Introduction of F-DOM to G-SOM-coated surfaces revealed competitive desorption of G-SOM from the organo-mineral interface. During F-DOM irrigation, high HIX values were observed in effluent solutions, indicating remobilization of G-SOM by displacement. According to spectroscopic analyses, the displaced G-SOM consisted of aromatic phenolic acids with high excitation-emission "fingerprints" characteristic of fulvic-and humic-acid-like compounds, providing evidence for kinetic DOM exchange reactions.
• Gao, X. D., Root, R. A., Farrell, J., Ela, W., & Chorover, J. (2013). Effect of silicic acid on arsenate and arsenite retention mechanisms on 6-L ferrihydrite: A spectroscopic and batch adsorption approach. Appl. Geochem., 38, 110-120.
• Heckman, K., Grandy, A. S., Gao, X. D., Keiluweit, M., Wickings, K., Carpenter, K., Chorover, J., & Rasmussen, C. (2013). Sorptive fractionation of organic matter and formation of organo-hydroxy-aluminum complexes during litter biodegradation in the presence of gibbsite.. Geochim. Cosmochim. Acta, 121, 667-683.
• Heckman, K., Grandy, A. S., Gao, X., Keiluweit, M., Wickings, K., Carpenter, K., Chorover, J., & Rasmussen, C. (2013). Sorptive fractionation of organic matter and formation of organo-hydroxy-aluminum complexes during litter biodegradation in the presence of gibbsite. Geochimica et Cosmochimica Acta, 121, 667-683.
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  Abstract: Solid and aqueous phase Al species are recognized to affect organic matter (OM) stabilization in forest soils. However, little is known about the dynamics of formation, composition and dissolution of organo-Al hydroxide complexes in microbially-active soil systems, where plant litter is subject to microbial decomposition in close proximity to mineral weathering reactions. We incubated gibbsite-quartz mineral mixtures in the presence of forest floor material inoculated with a native microbial consortium for periods of 5, 60 and 154days. At each time step, samples were density separated into light (2.0gcm-3) fractions. The light fraction was mainly comprised of particulate organic matter, while the intermediate and heavy density fractions contained moderate and large amounts of Al-minerals, respectively. Multi-method interrogation of the fractions indicated the intermediate and heavy fractions differed both in mineral structure and organic compound composition. X-ray diffraction analysis and SEM/EDS of the mineral component of the intermediate fractions indicated some alteration of the original gibbsite structure into less crystalline Al hydroxide and possibly proto-imogolite species, whereas alteration of the gibbsite structure was not evident in the heavy fraction. DRIFT, Py-GC/MS and STXM/NEXAFS results all showed that intermediate fractions were composed mostly of lignin-derived compounds, phenolics, and polysaccharides. Heavy fraction organics were dominated by polysaccharides, and were enriched in proteins, N-bearing compounds, and lipids. The source of organics appeared to differ between the intermediate and heavy fractions. Heavy fractions were enriched in 13C with lower C/N ratios relative to intermediate fractions, suggesting a microbial origin. The observed differential fractionation of organics among hydroxy-Al mineral types suggests that microbial activity superimposed with abiotic mineral-surface-mediated fractionation leads to strong density differentiation of organo-mineral complex composition even over the short time scales probed in these incubation experiments. The data highlight the strong interdependency of mineral transformation, microbial community activity, and organic matter stabilization during biodegradation. © 2013.
• Heckman, K., Welty-Bernard, A., Vazquez-Ortega, A., Schwartz, E., Chorover, J., & Rasmussen, C. (2013). The influence of goethite and gibbsite on soluble nutrient dynamics and microbial community composition. Biogeochem., 112, 179-195.
• Heckman, K., Welty-Bernard, A., Vazquez-Ortega, A., Schwartz, E., Chorover, J., & Rasmussen, C. (2013). The influence of goethite and gibbsite on soluble nutrient dynamics and microbial community composition. Biogeochemistry, 112(1-3), 179-195.
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  Abstract: Iron and aluminum (oxyhydr)oxides are ubiquitous in the soil environment and have the potential to strongly affect the properties of dissolved organic matter. We examined the effect of oxide surfaces on soluble nutrient dynamics and microbial community composition using an incubation of forest floor material in the presence of (1) goethite and quartz, (2) gibbsite and quartz, and (3) quartz surfaces. Forest floor material was incubated over a period of 154 days. Aqueous extracts of the incubations were harvested on days 5, 10, 20, 30, 60, 90, and 154, and concentrations of P, N, PO43-, NO2-, NO3-, and organic C were measured in the solutions. Microbial community composition was examined through pyrosequencing of bacterial and fungal small subunit ribosomal RNA genes on selected dates throughout the incubation. Results indicated that oxide surfaces exerted strong control on soluble nutrient dynamics and on the composition of the decomposer microbial community, while possibly having a small impact on system-level respiration. Goethite and gibbsite surfaces showed preferential adsorption of P-containing and high molar mass organic solutes, but not of N-containing compounds. On average, organic C concentrations were significantly lower in water extractable organic matter (WEOM) solutions from oxide treatments than from the control treatment (P = 0. 0037). Microbial community composition varied both among treatments and with increasing time of incubation. Variation in bacterial and fungal community composition exhibited strong-to-moderate correlation with length of incubation, and several WEOM physiochemical characteristics including apparent (weight averaged) molar mass, pH and electrical conductivity. Additionally, variation in bacterial community composition among treatments was correlated with total P (r = 0. 60, P < 0. 0001), PO43- (r = 0. 79, P < 0. 0001), and organic C (r = 0. 36, P = 0. 015) concentrations; while variation in fungal communities was correlated with organic C concentrations (r = -0. 48, P = 0. 0008) but not with phosphorus concentrations. The relatively small impact of oxide surfaces on system-level microbial respiration of organic matter despite their significant effects on microbial community composition and WEOM dynamics lends additional support to the theory of microbial functional redundancy. © 2012 Springer Science+Business Media B.V.
• Hernandez-Ruiz, S., Wickramasekara, S., Abrell, L., Gao, X., Chefetz, B., & Chorover, J. (2013). Complexation of trace organic contaminants with fractionated dissolved organic matter: implications for mass spectrometric quantification. Chemosphere, 91(3).
• Pelletier, J. D., Breshears, D. D., Barron-Gafford, G. A., Brooks, P. D., Chorover, J., Durick, M., Harman, C. J., Huxman, T. E., Lohse, K. A., Lybrand, R., Meixner, T., Mcintosh, J. C., Papuga, S. A., Rasmussen, C., Schaap, M. G., Swetnam, T. L., & Troch, P. A. (2013). Coevolution of nonlinear trends in vegetation, soils, and topography with elevation and slope aspect: A case study in the sky islands of southern Arizona. Journal of Geophysical Research - Earth Surface, 118(2), 1-18.
• Root, R. A., Fathordoobadi, S., Alday, F., Ela, W., & Chorover, J. (2013). Microscale speciation of arsenic and iron in ferric-based sorbents subjected to simulated landfill conditions. Environmental science & technology, 47(22).
• Ruiz, S. H., Wickramasekara, S., Abrell, L., Gao, X., Chefetz, B., & Chorover, J. (2013). Complexation of trace organic contaminants with fractionated dissolved organic matter: Implications for mass spectrometric quantification. Chemosphere, 91(3), 344-350.
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  PMID: 23276460;Abstract: Interaction with aqueous phase dissolved organic matter (DOM) can alter the fate of trace organic contaminants of emerging concern once they enter the water cycle. In order to probe possible DOM binding mechanisms and their consequences for contaminant detection and quantification in natural waters, a set of laboratory experiments was conducted with aqueous solutions containing various operationally-defined "hydrophilic" and "hydrophobic" freshwater DOM fractions isolated by resin adsorption techniques from reference Suwannee River natural organic matter (SROM). Per unit mass of SROM carbon, hydrophobic acids (HoA) comprised the largest C fraction (0.63±0.029), followed by hydrophilic-neutrals (HiN, 0.11±0.01) and acids (HiA, 0.09±0.017). Aqueous solutions comprising 8mgL-1 DOC of each SROM fraction were spiked with a concentration range (10-1000μgL-1) of bisphenol A (BPA), carbamazepine (CBZ), or ibuprofen (IBU) as model target compounds in 24mM NH4HCO3 background electrolyte at pH 7.4. Contaminant interaction with the SROM fractions was probed using fluorescence spectroscopy, and effects on quantitative analysis of the target compounds were measured using direct aqueous-injection liquid chromatography tandem mass spectrometry (LC-MS/MS). Total quenching was greater for the hydrophilic fractions of SROM and associations were principally with protein-like and fulvic acid-like constituents. Whereas LC-MS/MS recoveries indicated relatively weak interactions with most SROM factions, an important exception was the HiA fraction, which diminished recovery of CBZ and IBU by ca. 30% and 70%, respectively, indicating relatively strong molecular interactions. © 2012 Elsevier Ltd.
• Thompson, A., Amistadi, M. K., Chadwick, O. A., & Chorover, J. (2013). Fractionation of yttrium and holmium during basaltic soil weathering. Geochim. Cosmochim. Acta, 119, 18-30.
• Thompson, A., Amistadi, M. K., Chadwick, O. A., & Chorover, J. (2013). Fractionation of yttrium and holmium during basaltic soil weathering. Geochimica et Cosmochimica Acta, 119, 18-30.
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  Abstract: The anomalously low affinity of yttrium (Y) for iron (Fe) (oxyhydr)oxides relative to lanthanides with similar ionic radius (e.g., Ho) has been demonstrated in experiments with isolated Fe minerals and in a variety of marine systems that contain high concentrations of solid phase Fe. However, it has not previously been demonstrated to occur during soil genesis, despite the common observation that many soils become enriched in Fe over time. We hypothesized that Y would become progressively depleted in soils relative to Ho with increased weathering. Since, trivalent Y has an anomalously low Misono softness relative to other trivalent ions included in the rare earth element and yttrium group (REY3+), we also investigated whether soil REY fractionation reflects variation in Misono softness. To test this, we measured trends in total REY concentrations for Hawaiian soils derived from basaltic parent materials aged 0.3-4100ky, and measured REYs released from the same samples during short-time (3h) dissolution experiments conducted as part of a previous investigation linking dissolution with surface charge properties (Chorover et al., 2004). The chondrite-normalized Y/Ho ratios in the parent Hawaiian basalt (Chond[Y/Ho]=0.998) and continental dust (Chond[Y/Ho]=0.994) inputs are remarkably similar, and thus we can interpret deviations from Chond[Y/Ho]~1.0 to result from soil biogeochemical processes and not source mixing. Between 0.3 and 20ky, the Chond[Y/Ho] ratio of the subsurface soils decreased from 0.96±0.07(2σ) to 0.71±0.05, and then remained unchanged across the rest of the weathering sequence. In contrast, the Chond[Y/Ho] ratio of the surface soils decreased from 0.99±0.07 to 0.76±0.05 at 150ky and then, most likely due to continued dust inputs, increased to 1.04±0.07 in the oldest soils. Analysis of the short-time dissolution experiments revealed preferential release of Y relative to Ho (and also La relative Pr) at intermediate pH where aqueous REY concentrations are governed by proton competition for adsorption sites. Proton-competition-control over REY release is bounded at high pH by the onset of colloidal dispersion-represented by the point of minimum dissolution (p.m.d.) of Al-and at low pH by the soil's point of zero net charge (p.z.n.c.) and/or when proton-promoted dissolution of REY-containing solids, including Fe-(oxyhydr)oxides, control REY release. Results of our dissolution experiments suggest that complexation of REYs by dissolved organic matter (DOM) does not drive Y-Ho fractionation during pedogenesis, but rather may suppress it. Synthesis of these field and laboratory experiments suggests the Y/Ho ratio decreases early in soil development (
• Valentin-Vargas, A., Chorover, J., & Maier, R. M. (2013). A new standard-based polynomial interpolation (SBPln) method to address gel-to-gel variability for the comparison of multiple denaturing gradient gel electrophoresis profile matrices. J. Microbiol. Meth., 92, 173-177.
• , F., White, S., Borrillo, H. T., Amistadi, M., Root, R., Chorover, J., & Maier, R. (2012). Response of key soil parameters during phytostabilization in extremely acidic tailings: effect of plant species. Environ. Sci. Technol, 46, 1019-1027.
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  PMC3263829
• Elzinga, E. J., Huang, J., Chorover, J., & Kretzschmar, R. (2012). ATR-FTIR Spectroscopy Study of the Influence of pH and Contact Time on the Adhesion of Shewanella putrefaciens Bacterial Cells to the Surface of Hematite. Environ. Sci. Tech, 46(23), 12848-12855.
• Elzinga, E. J., Huang, J., Chorover, J., & Kretzschmar, R. (2012). ATR-FTIR spectroscopy study of the influence of ph and contact time on the adhesion of shewanella putrefaciens bacterial cells to the surface of hematite. Environmental Science and Technology, 46(23), 12848-12855.
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  PMID: 23136883;Abstract: Attachment of live cells of Shewanella putrefaciens strain CN-32 to the surface of hematite (α-Fe2O3) was studied with in situ ATR-FTIR spectroscopy at variable pH (4.5-7.7) and contact times up to 24 h. The IR spectra indicate that phosphate based functional groups on the cell wall play an important role in mediating adhesion through formation of inner-sphere coordinative bonds to hematite surface sites. The inner-sphere attachment mode of microbial P groups varies with pH, involving either a change in protonation or in coordination to hematite surface sites as pH is modified. At all pH values, spectra collected during the early stages of adhesion show intense IR bands associated with reactive P-groups, suggestive of preferential coordination of P-moieties at the hematite surface. Spectra collected after longer sorption times show distinct frequencies from cell wall protein and carboxyl groups, indicating that bacterial adhesion occurring over longer time scales is to a lesser degree associated with preferential attachment of P-based bacterial functional groups to the hematite surface. The results of this study demonstrate that pH and reaction time influence cell-mineral interactions, implying that these parameters play an important role in determining cell mobility and biofilm formation in aqueous geochemical environments. © 2012 American Chemical Society.
• Gao, X., & Chorover, J. (2012). Adsorption of perfluorooctanoic acid and perfluorooctanesulfonic acid to iron oxide surfaces as studied by flow-through ATR-FTIR spectroscopy. Environmental Chemistry, 9(2), 148-157.
• Hernandez-Ruiz, S., Abrell, L., Wickramasekara, S., Chefetz, B., & Chorover, J. (2012). Quantifying PPCP interaction with dissolved organic matter in aqueous solution: Combined use of fluorescence quenching and tandem mass spectrometry. Water Research, 46(4), 943-954.
• Kramer, M. G., Sanderman, J., Chadwick, O. A., Chorover, J., & Vitousek, P. M. (2012). Long-term carbon storage through retention of dissolved aromatic acids by reactive particles in soil. Global Change Biology, 18(8), 2594-2605.
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  Abstract: Soils retain large quantities of carbon, thereby slowing its return to the atmosphere. The mechanisms governing organic carbon sequestration in soil remain poorly understood, yet are integral to understanding soil-climate feedbacks. We evaluated the biochemistry of dissolved and solid organic carbon in potential source and sink horizons across a chronosequence of volcanic soils in Hawai'i. The soils are derived from similar basaltic parent material on gently sloping volcanic shield surfaces, support the same vegetation assemblage, and yet exhibit strong shifts in soil mineralogy and soil carbon content as a function of volcanic substrate age. Solid-state 13carbon nuclear magnetic resonance spectra indicate that the most persistent mineral-bound carbon is comprised of partially oxidized aromatic compounds with strong chemical resemblance to dissolved organic matter derived from plant litter. A molecular mixing model indicates that protein, lipid, carbohydrate, and char content decreased whereas oxidized lignin and carboxyl/carbonyl content increased with increasing short-range order mineral content. When solutions rich in dissolved organic matter were passed through Bw-horizon mineral cores, aromatic compounds were preferentially sorbed with the greatest retention occurring in horizons containing the greatest amount of short-range ordered minerals. These minerals are reactive metastable nanocrystals that are most common in volcanic soils, but exist in smaller amounts in nearly all major soil classes. Our results indicate that long-term carbon storage in short-range ordered minerals occurs via chemical retention with dissolved aromatic acids derived from plant litter and carried along preferential flow-paths to deeper B horizons. © 2012 Blackwell Publishing Ltd.
• Kramer, M., Sanderman, J., Chadwick, O., Chorover, J., & Vitousek, P. (2012). Long-term carbon storage through retention of dissolved aromatic acids by reactive particles in soil. Global Change Biology, 18, 2594-2605.
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  doi: 10.1111/j.1365-2486.2012.02681.x
• Mueller, K. E., Eissenstat, D. M., Hobbie, S. E., Oleksyn, J., Jagodzinski, A. M., Reich, P. B., Chadwick, O. A., & Chorover, J. (2012). Tree species effects on coupled cycles of carbon, nitrogen, and acidity in mineral soils at a common garden experiment. Biogeochemistry, 111(1-3), 601-614.
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  Abstract: Forest biogeochemical cycles are shaped by effects of dominant tree species on soils, but the underlying mechanisms are not well understood. We investigated effects of temperate tree species on interactions among carbon (C), nitrogen (N), and acidity in mineral soils from an experiment with replicated monocultures of 14 tree species. To identify how trees affected these soil properties, we evaluated correlations among species-level characteristics (e. g. nutrient concentrations in leaf litter, wood, and roots), stand-level properties (e. g. nutrient fluxes through leaf litterfall, nutrient pools in stemwood), and components of soil C, N, and cation cycles. Total extractable acidity (aciditytot) was correlated positively with mineral soil C stocks (R2 = 0. 72, P < 0. 001), such that a nearly two-fold increase in aciditytot was associated with a more than two-fold increase of organic C. We attribute this correlation to effects of tree species on soil acidification and subsequent mineral weathering reactions, which make hydrolyzing cations available for stabilization of soil organic matter. The effects of tree species on soil acidity were better understood by measuring multiple components of soil acidity, including pH, the abundance of hydrolyzing cations in soil solutions and on cation exchange sites, and aciditytot. Soil pH and aciditytot were correlated with proton-producing components of the soil N cycle (e. g. nitrification), which were positively correlated with species-level variability in fine root N concentrations. Soluble components of soil acidity, such as aluminum in saturated paste extracts, were more strongly related to plant traits associated with calcium cycling, including leaf and root calcium concentrations. Our results suggest conceptual models of plant impacts on soil biogeochemistry should be revised to account for underappreciated plant traits and biogeochemical processes. © 2012 Springer Science+Business Media B.V.
• Mueller, K., Eissenstat, D., Hobbie, S., Oleksyn, J., Jagodzinski, A., Reich, P., Chadwick, O., & Chorover, J. (2012). Tree species effects on coupled cycles of carbon, nitrogen, and acidity in mineral soils at a common garden experiment. Biogeochemistry, 111(1-3), 601-614.
• Perdrial, J. N., Perdrial, N., Harpold, A., Gao, X., Gabor, R., LaSharr, K., & Chorover, J. (2012). Impacts of sampling dissolved organic matter with passive capillary wicks versus aqueous soil extraction. Soil Science Society of America Journal, 76(6), 2019-2030.
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  Abstract: Quantitative characterization of dissolved organic matter (DOM) in soil and vadose zone solution is needed to interpret mechanisms of nutrient and C cycling as well as bio-weathering processes. Passive capillary wick samplers (PCaps) are useful for soil solution sampling because they can provide measures of water and associated DOM-constituent flux in the unsaturated zone, however potential impacts of the wick material on DOM chemical properties has not been investigated yet. We therefore conducted experiments where aqueous soil extracts were transported along PCap fiberglass wicks in flow-through experiments. Results indicated limited dissolved organic carbon (DOC) sorption and DOM fractionation, and related parameters (total dissolved nitrogen [TDN], DOM fluorescence components) also remained largely unaffected. We note that this experiment does not account for the extent to which soil hydrologic processes may be affected by PCap field installations. However, given that the wicks did not fractionate significantly DOM we compared field-based PCap DOM solution collected in situ with laboratory-based aqueous soil extraction (ASE) of DOM from the same soils to assess differences in DOM quality. Spectroscopic analysis of DOM in ASE solutions showed lower O-H stretch/carboxlyate band intensity ratios, more pronounced aliphatic C-H stretching (Fourier Transform Infrared analysis) higher specific ultraviolet-absorbance (SUVA254) values as well as greater abundance of fluorescence components in the region attributed to fulvic acids. We conclude that difference in molecular properties of DOM derived from laboratory ASE vs. PCap field collection of the same soils is attributable to differential disturbance effects of the two methods of soil solution collection. © Soil Science Society of America.
• Perdrial, J., Perdrial, N., Harpold, A., Gao, X., Gabor, R., LaSharr, K., & Chorover, J. (2012). Impacts of Sampling Dissolved Organic Matter with Passive Capillary Wicks Versus Aqueous Soil Extraction. Soil Sci. Soc. Am. J, 76, 2019-2030.
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  10.2136/sssaj2012.0061.
• Wickramasekara, S., , S., Abrell, L., Arnold, R., & Chorover, J. (2012). Natural dissolved organic matter affects electrospray ionization during analysis of emerging contaminants by mass spectrometry. Analytica Chimica Acta, 717, 77-84.
• Bern, C. R., Chadwick, O. A., Hartshorn, A. S., Khomo, L. M., & Chorover, J. (2011). A mass-balance model to separate and quantify colloidal and solute redistributions in soil. Chemical Geology, 282(3-4), 113-119.
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  Abstract: Studies of weathering and pedogenesis have long used calculations based upon low solubility index elements to determine mass gains and losses in open systems. One of the questions currently unanswered in these settings is the degree to which mass is transferred in solution (solutes) versus suspension (colloids). Here we show that differential mobility of the low solubility, high field strength (HFS) elements Ti and Zr can trace colloidal redistribution, and we present a model for distinguishing between mass transfer in suspension and solution. The model is tested on a well-differentiated granitic catena located in Kruger National Park, South Africa. Ti and Zr ratios from parent material, soil and colloidal material are substituted into a mixing equation to quantify colloidal movement. The results show zones of both colloid removal and augmentation along the catena. Colloidal losses of 110kgm-2 (-5% relative to parent material) are calculated for one eluviated soil profile. A downslope illuviated profile has gained 169kgm-2 (10%) colloidal material. Elemental losses by mobilization in true solution are ubiquitous across the catena, even in zones of colloidal accumulation, and range from 1418kgm-2 (-46%) for an eluviated profile to 195kgm-2 (-23%) at the bottom of the catena. Quantification of simultaneous mass transfers in solution and suspension provide greater specificity on processes within soils and across hillslopes. Additionally, because colloids include both HFS and other elements, the ability to quantify their redistribution has implications for standard calculations of soil mass balances using such index elements. © 2011.
• Bern, C., Chadwick, O., Hartshorn, A., Khomo, L., & Chorover, J. (2011). A mass-balance model to separate and quantify colloidal and solute redistributions in soil. Chem. Geol, 282, 113-119.
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  doi:10.1016/j.chemgeo.2011.01.014.
• Chang, H., Um, W., Rod, K., Serne, R., Thompson, A., Perdrial, N., Steefel, I., & Chorover, J. (2011). Strontium and cesium release mechanisms during unsaturated flow through waste-weathered Hanford sediments. Environ. Sci. Technol, 45, 8313-8320.
• Chang, H., Wooyong, U. m., Rod, K., Serne, R. J., Thompson, A., Perdrial, N., Steefel, C. I., & Chorover, J. (2011). Strontium and cesium release mechanisms during unsaturated flow through waste-weathered Hanford sediments. Environmental Science and Technology, 45(19), 8313-8320.
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  PMID: 21859142;Abstract: Leaching behavior of Sr and Cs in the vadose zone of Hanford site (Washington) was studied with laboratory-weathered sediments mimicking realistic conditions beneath the leaking radioactive waste storage tanks. Unsaturated column leaching experiments were conducted using background Hanford pore water focused on first 200 pore volumes. The weathered sediments were prepared by 6 months reaction with a synthetic Hanford tank waste leachate containing Sr and Cs (10 -5 and 10 -3 molal representative of LO- and HI-sediment, respectively) as surrogates for 90Sr and 137Cs. The mineral composition of the weathered sediments showed that zeolite (chabazite-type) and feldspathoid (sodalite-type) were the major byproducts but different contents depending on the weathering conditions. Reactive transport modeling indicated that Cs leaching was controlled by ion-exchange, while Sr release was affected primarily by dissolution of the secondary minerals. The later release of K, Al, and Si from the HI-column indicated the additional dissolution of a more crystalline mineral (cancrinite-type). A two-site ion-exchange model successfully simulated the Cs release from the LO-column. However, a three-site ion-exchange model was needed for the HI-column. The study implied that the weathering conditions greatly impact the speciation of the secondary minerals and leaching behavior of sequestrated Sr and Cs. © 2011 American Chemical Society.
• Chorover, J., Troch, P. A., Rasmussen, C., Brooks, P. D., Pelletier, J. D., Breshears, D. D., Huxman, T. E., Kurc, S. A., Lohse, K., Mcintosh, J. C., Meixner, T., Schaap, M. G., Litvak, M., Perdrial, J., Harpold, A., & Durcik, M. (2011). How water, carbon, and energy drive critical zone evolution: the Jemez-Santa Catalina Critical Zone Observatory. Vadose Zone Journal, 10, 884-899.
• Chorover, J., Troch, P., Rasmussen, C., Brooks, P., Pelletier, J., Breshears, D., Huxman, T., Kurc, S., Lohse, K., McIntosh, J., Meixner, T., Schaap, M., Litvak, M., Perdrial, J., Harpold, A., & Durcik, M. (2011). How water, carbon, and energy drive landscape evolution and surface water dynamics: The Jemez River Basin. Vadose Zone J., Special Issue on the Critical Zone, 10, 884-889.
• Gao, X., & Chorover, J. (2011). Langmuir, 27, 5936-5943.
• Gao, X., & Chorover, J. (2011). Amphiphile disruption of pathogen attachment at the hematite (α-Fe₂O₃)-Water Interface. Langmuir, 27(10), 5936-5943.
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  PMID: 21488611;Abstract: Prior studies have indicated that the subsurface transport of Cryptosporidium parvum oocysts is diminished in sediments containing iron oxides and that inner-sphere complexation of oocyst surficial carboxylate plays a role in the retardation. However, the impacts of natural organic matter (NOM) remain poorly understood. In this study, we used a model anionic surfactant, sodium dodecyl sulfate (SDS), as a surrogate for amphiphilic NOM components to examine the impacts of amphiphilic components on oocyst adhesion mechanisms. We employed in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy to determine the effects of SDS on the molecular bonds that mediate interactions between oocyst surficial biomolecules and hematite (R-Fe 2O3) surface functional groups over a wide range of solution pH. The results show that the presence of SDS significantly diminishes Fe-carboxylate complexation, as indicated by progressive decreases in intensity of asymmetric and symmetric stretching vibrations of carboxylate [vas(COO -) and vs(COO-)] with reaction time. In addition, one of the vs(COO-) bands shifted from 1370 to 1418 cm-1 upon SDS introduction, suggesting that SDS also changed the complexation mode. The data indicate that competition from the sulfonate groups (OSO3-) of SDS at R-Fe2O3 surface sites is a primary mechanism resulting in decreased Fe-carboxylate complexation. Sorptive competition from amphiphilic NOM components may therefore increase the mobility of C. parvum oocysts in the environment through disruption of interfacial pathogen-mineral surface bonds. © 2011 American Chemical Society.
• Harvey, R. W., Metge, D. W., Mohanram, A., Gao, X., & Chorover, J. (2011). Differential effects of dissolved organic carbon upon re-entrainment and surface properties of groundwater bacteria and bacteria-sized microspheres during transport through a contaminated, sandy aquifer. Environmental Science and Technology, 45(8), 3252-3259.
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  PMID: 21275400;Abstract: Injection-and-recovery studies involving a contaminated, sandy aquifer (Cape Cod, Massachusetts) were conducted to assess the relative susceptibility for in situ re-entrainment of attached groundwater bacteria (Pseudomonas stuzeri ML2, and uncultured, native bacteria) and carboxylate-modified microspheres (0.2 and 1.0 μm diameters). Different patterns of re-entrainment were evident for the two colloids in response to subsequent injections of groundwater (hydrodynamic perturbation), deionized water (ionic strength alteration), 77 μM linear alkylbenzene sulfonates (LAS, anionic surfactant), and 76 μM Tween 80 (polyoxyethylene sorbitan monooleate, a very hydrophobic nonionic surfactant). An injection of deionized water was more effective in causing detachment of micrsopheres than were either of the surfactants, consistent with the more electrostatic nature of microsphere's attachment, their extreme hydrophilicity (hydrophilicity index, HI, of 0.99), and negative charge (zeta potentials, Χ, of -44 to -49 mv). In contrast, Tween 80 was considerably more effective in re-entraining the more-hydrophobic native bacteria. Both the hydrophilicities and zeta potentials of the native bacteria were highly sensitive to and linearly correlated with levels of groundwater dissolved organic carbon (DOC), which varied modestly from 0.6 to 1.3 mg L-1. The most hydrophilic (0.52 HI) and negatively charged (Χ -38.1 mv) indigenous bacteria were associated with the lowest DOC. FTIR spectra indicated the latter community had the highest average density of surface carboxyl groups. In contrast, differences in groundwater (DOC) had no measurable effect on hydrophilicity of the bacteria-sized microspheres and only a minor effect on their Χ. These findings suggest that microspheres may not be very good surrogates for bacteria in field-scale transport studies and that adaptive (biological) changes in bacterial surface characteristics may need to be considered where there is longer-term exposure to contaminant DOC. © 2011 American Chemical Society.
• Harvey, R., Metge, D., Mohanram, A., Gao, X., & Chorover, J. (2011). Differential effects of dissolved organic carbon upon re-entrainment and surface properties of groundwater bacteria and bacteria-sized microspheres during transport through a contaminated, sandy aquifer. Environ. Sci. Technol, 45, 3252-3259.
• Hayes, S., O, D. P., Webb, S., Maier, R., & Chorover, J. (2011). Changes in zinc speciation with mine tailings acidification in an arid weathering environment. Environ. Sci. Technol, 45, 7166-7172.
• Heckman, K., Vazquez-Ortega, A., Gao, X., Chorover, J., & Rasmussen, C. (2011). Changes in water extractable organic matter during incubation of forest floor material in the presence of quartz, goethite and gibbsite surfaces. Geochim. Cosmochim. Acta, 75, 4295-4309.
• Heckman, K., Vazquez-Ortega, A., Gao, X., Chorover, J., & Rasmussen, C. (2011). Changes in water extractable organic matter during incubation of forest floor material in the presence of quartz, goethite and gibbsite surfaces. Geochimica et Cosmochimica Acta, 75(15), 4295-4309.
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  Abstract: The release of dissolved organic matter (DOM) from forest floor material constitutes a significant flux of C to the mineral soil in temperate forest ecosystems, with estimates on the order of 120-500kgCha-1year-1. Interaction of DOM with minerals and metals results in sorptive fractionation and stabilization of OM within the soil profile. Iron and aluminum oxides, in particular, have a significant effect on the quantity and quality of DOM transported through forest soils due to their high surface area and the toxic effects of dissolved aluminum on microbial communities. We directly examined these interactions by incubating forest floor material, including native microbiota, for 154days in the presence of (1) goethite (α-FeOOH), (2) gibbsite (γ-Al(OH)3), and (3) quartz (α-SiO2) sand (as a control). Changes in molecular and thermal properties of water extractable organic matter (WEOM, as a proxy for DOM) were evaluated. WEOM was harvested on days 5, 10, 20, 30, 60, 90, and 154, and examined by thermogravimetry/differential thermal analysis (TG/DTA) and diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy. Results indicated significant differences in WEOM quality among treatments, though the way in which oxide surfaces influenced WEOM properties did not seem to change significantly with increasing incubation time. Dissolved organic C concentrations were significantly lower in WEOM from the oxide treatments in comparison to the control treatment. Incubation with goethite produced WEOM with mid-to-high-range thermal lability that was depleted in both protein and fatty acids relative to the control. The average enthalpy of WEOM from the goethite treatment was significantly higher than either the gibbsite or control treatment, suggesting that interaction with goethite surfaces increases the energy content of WEOM. Incubation with gibbsite produced WEOM rich in thermally recalcitrant and carboxyl-rich compounds in comparison to the control treatment. These data indicate that interaction of WEOM with oxide surfaces significantly influences the composition of WEOM and that oxides play an important role in determining the biogeochemistry of forest soil DOM. © 2011.
• Mikutta, R., Zang, U., Chorover, J., Haumaier, L., & Kalbitz, K. (2011). Stabilization of extracellular polymeric substances (Bacillus subtilis) by adsorption to and coprecipitation with Al forms. Geochimica et Cosmochimica Acta, 75(11), 3135-3154.
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  Abstract: Extracellular polymeric substances (EPS) are continuously produced by bacteria during their growth and metabolism. In soils, EPS are bound to cell surfaces, associated with biofilms, or released into solution where they can react with other solutes and soil particle surfaces. If such reaction results in a decrease in EPS bioaccessibility, it may contribute to stabilization of microbial-derived organic carbon (OC) in soil. Here we examined: (i) the chemical fractionation of EPS produced by a common Gram positive soil bacterial strain (Bacillus subtilis) during reaction with dissolved and colloidal Al species and (ii) the resulting stabilization against desorption and microbial decay by the respective coprecipitation (with dissolved Al) and adsorption (with Al(OH)3(am)) processes. Coprecipitates and adsorption complexes obtained following EPS-Al reaction as a function of pH and ionic strength were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The stability of adsorbed and coprecipitated EPS against biodegradation was assessed by mineralization experiments for 1100h. Up to 60% of the initial 100mg/L EPS-C was adsorbed at the highest initial molar Al:C ratio (1.86), but this still resulted only in a moderate OC mass fraction in the solid phase (17mg/g Al(OH)3(am)). In contrast, while coprecipitation by Al was less efficient in removing EPS from solution (maximum values of 33% at molar Al:C ratios of 0.1-0.2), the OC mass fraction in the solid product was substantially larger than that in adsorption complexes. Organic P compounds were preferentially bound during both adsorption and coprecipitation. Data are consistent with strong ligand exchange of EPS phosphoryl groups during adsorption to Al(OH)3(am), whereas for coprecipitation weaker sorption mechanisms are also involved. X-ray photoelectron analyses indicate an intimate mixing of EPS with Al in the coprecipitates, which is not observed in the case of EPS adsorption complexes. The incubation experiments showed that both processes result in overall stabilization of EPS against microbial decay. Stabilization of adsorbed or coprecipitated EPS increased with increasing molar Al:C ratio and biodegradation was correlated with EPS desorption, implying that detachment of EPS from surface sites is a prerequisite for microbial utilization. Results indicate that the mechanisms transferring EPS into Al-organic associations may significantly affect the composition and stability of biomolecular C, N and P in soils. The observed efficient stabilization of EPS might explain the strong microbial character of organic matter in subsoils. © 2011 Elsevier Ltd.
• Mikutta, R., Zhang, U., Chorover, J., Haumaier, L., & Kalbitz, K. (2011). Stabilization of extracellular polymeric substances by adsorption versus co-precipitation with hydroxyl-aluminum species. Geochim. Cosmochim. Acta, 75, 3135-3154.
• Navon, R., Hernandes-Ruiz, S., Chorover, J., & Chefetz, B. (2011). Interactions of carbamazepine in soil: Effects of dissolved organic matter. J. Environ. Qual, 40, 942-948.
• Navon, R., Hernandez-Ruiz, S., Chorover, J., & Chefetz, B. (2011). Interactions of carbamazepine in soil: Effects of dissolved organic matter. Journal of Environmental Quality, 40(3), 942-948.
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  PMID: 21546680;Abstract: Pharmaceutical compounds (PCs) and dissolved organic matter (DOM) are co-introduced into soils by irrigation with reclaimed wastewater. We targeted carbamazepine (CBZ) as a model compound to study the tertiary interactions between relatively polar PCs, DOM, and soil. Sorption-desorption behavior of CBZ was studied with bulk clay soil and the corresponding clay size fraction in the following systems: (i) without DOM, (ii) co-introduced with DOM, and (iii) pre-adsorption of DOM before CBZ introduction. Sorption of the DOM to both sorbents was irreversible and exhibited pronounced sorption- desorption hysteresis. Carbamazepine exhibited higher sorption affinity and nonlinearity, and a higher degree of desorption hysteresis with the bulk soil than the corresponding clay size fraction. Th is was probably due to specific interactions with polar soil organic matter fractions that are more common in the bulk soil. Co-introduction of CBZ and DOM to the soil did not significantly aff ect the sorption behavior of CBZ; however, following pre-adsorption of DOM by the bulk soil, an increase in sorption affinity and decrease in sorption linearity were observed. In this latter treatment, desorption hysteresis of CBZ was significantly increased for both sorbents. We hypothesize that this was due to either strong chemical interactions of CBZ with the adsorbed DOM or physical encapsulation of CBZ in DOM-clay complexes. Based on this study, we suggest that DOM facilitates stronger interactions of polar PCs with the solid surface. Th is mechanism can reduce PC desorption ability in soils. © 2011 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.
• Pelletier, J., McGuire, L., Ash, J., Engelder, T., Hill, L., Leroy, K., Orem, C., Rosenthal, W., Trees, M., Rasumussen, C., & Chorover, J. (2011). Calibration and testing of upland hillslope evolution models in a dated landscape: Banco Bonito, New Mexico. J. Geophys. Res. Earth Surface, 116.
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  DOI 10.1029/2011JF001976
• Perdrial, N., Rivera, N., Thompson, A., O'Day, P. A., & Chorover, J. (2011). Trace contaminant concentration affects mineral transformation and pollutant fate in hydroxide-weathered Hanford sediments. Journal of Hazardous Materials, 197, 119-127.
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  PMID: 21993146;Abstract: Prior work has shown that when silicaceous sediments are infused with caustic radioactive waste, contaminant fate is tightly coupled to ensuing mineral weathering reactions. However, the effects of local aqueous geochemical conditions on these reactions are poorly studied. Thus, we varied contaminant concentration and pCO 2 during the weathering of previously uncontaminated Hanford sediments over 6 months and 1 year in a solution of caustic waste (pH 13, high ionic strength). Co-contaminants Sr, Cs and I were added at " low" (Cs/Sr: 10 -5m; I: 10 -7m) and " high" (Cs/Sr: 10 -3m; I: 10 -5m) concentrations, and headspace was held at atmospheric or undetectable (
• Perdrial, N., Thompson, A., Rivera, N., Day, P., & Chorover, J. (2011). Trace contaminant and CO2 concentrations affect mineral transformation and pollutant fate in hydroxide-weathered Hanford sediments. J. Haz. Mat, 197, 119-127.
• Rivera, N., Choi, S., Strepka, C., Mueller, K., Perdrial, N., Chorover, J., & O'Day, P. A. (2011). Cesium and strontium incorporation into zeolite-type phases during homogeneous nucleation from caustic solutions. American Mineralogist, 96(11-12), 1809-1820.
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  Abstract: Formation of faujasite- and sodalite/cancrinite-type phases associated with caustic waste reactions in the environment may structurally incorporate contaminant species such as radioactive Sr2+ and Cs+, and thus provide a mechanism of attenuation. To investigate mineral evolution and structural incorporation of cations in simplified experiments, aluminosilicate solids were precipitated homogeneously at room temperature from batch solutions containing a 1:1 molal ratio of Si to Al and 10-3 molal Sr and/or Cs, and aged for 30 or 548 days. Syntheses were done with solutions in equilibrium with atmospheric CO2 and with gas-purged solutions. Experimental products were characterized by bulk chemical analyses, chemical extractions, XRD, SEM/TEM, TGA, solid-state 27Al NMR, and Sr EXAFS. Chemical analysis showed that solids had a 1:1 Al:Si molar ratio, and that Sr was sequestered at higher amounts than Cs. After 30 days of aging in purged solutions, XRD showed that zeolite X (faujasite-type) was the only crystalline product. After aging 30 and 548 days in solutions equilibrated with atmospheric CO2, a mixture of sodalite, cancrinite, and minor zeolite X were produced. Surface areas of solids at 30 days were much lower than published values for zeolite phases synthesized at high temperature, although particle aging produced more crystalline and less aggregated phases with higher bulk surface areas. Characterization of products by 27Al NMR indicated only tetrahedrally coordinated Al. Measured isotropic shifts of primary resonances did not change substantially with precipitate aging although the primary mineral phase changed from zeolite X to sodalite/cancrinite, indicating local ordering of Al-Si tetrahedra. Analysis of reaction products by Sr EXAFS suggested Sr bonding in hexagonal prisms and six-membered rings of the supercages of zeolite X that may be more site specific than those of monovalent cations. For samples aged for 548 days, interatomic distances from Sr-EXAFS are consistent with partial Sr dehydration and bonding to framework oxygen atoms in sodalite cages or in large channels in cancrinite. Incorporation of Sr into both faujasite and sodalite/cancrinite phases is favored over Cs during room-temperature synthesis, possibly because of increased cation site competition between Cs+ and Na+. Results of this study help to constrain cation incorporation into sodalite/cancrinite mineral assemblages that form at caustic waste-impacted field sites and may aid in the predictive modeling of contaminant release. © 1997-2011 Mineralogical Society of America.
• Rivera, N., Choi, S., Strepka, C., Mueller, K., Perdrial, N., Chorover, J., & O, D. P. (2011). Cesium and strontium incorporation into zeolite-type phases during homogeneous nucleation from caustic solutions. Am. Mineral, 96, 1809-1820.
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  DOI: 10.2138/am.2011.3789.
• Solis-Dominguez, F., Valentin-Vargas, A., Chorover, J., & Maier, R. (2011). Effect of arbuscular mycorrhizal fungi on plant biomass and the rhizosphere microbial community structure of mesquite grown in acidic lead/zinc mine tailings. Sci. Total Environ, 409, 1009-1016.
• Thompson, A., Rancourt, D. G., Chadwick, O. A., & Chorover, J. (2011). Iron solid-phase differentiation along a redox gradient in basaltic soils. Geochimica et Cosmochimica Acta, 75(1), 119-133.
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  Abstract: Iron compounds in soil are multifunctional, providing physical structure, ion sorption sites, catalytic reaction-centers, and a sink for respiratory electrons. Basaltic soils contain large quantities of iron that reside in different mineral and organic phases depending on their age and redox status. We investigated changes in soil iron concentration and its solid-phase speciation across a single-aged (400ky) lava flow subjected to a gradient in precipitation (2200-4200mmyr-1) and hence redox history. With increasing rainfall and decreasing Eh, total Fe decreased from about 25% to
• Thompson, A., Rancourt, D., Chadwick, O., & Chorover, J. (2011). Iron solid-phase differentiation along a redox gradient in basaltic soils. Geochim. Cosmochim. Acta, 75, 119-133.
• Cagnasso, M., Boero, V., Franchini, M. A., & Chorover, J. (2010). ATR-FTIR studies of phospholipid vesicle interactions with α-FeOOH and α-Fe₂O₃ surfaces. Colloids and Surfaces B: Biointerfaces, 76(2), 456-467.
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  PMID: 20074916;Abstract: Prior infrared spectroscopic studies of extracellular polymeric substances (EPS) and live bacterial cells have indicated that organic phosphate groups mediate cell adhesion to iron oxides via inner-sphere P-OFe surface complexation. Since cell membrane phospholipids are a potential source of organic phosphate groups, we investigated the adhesion of phospholipidic vesicles to the surfaces of the iron (oxyhydr)oxides goethite (α-FeOOH) and hematite (α-Fe2O3) using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. l-α-Phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidic acid (PA) were used because they are vesicle forming phospholipids representative of prokaryotic and eukaryotic cell surface membranes. Phospholipid vesicles, formed in aqueous suspension, were characterized by transmission electron microscopy (TEM), multi-angle laser light scattering (MALS) and quasi-elastic light scattering (QELS). Their adhesion to goethite and hematite surfaces was studied with ATR-FTIR at pH 5. Results indicate that PC and PE adsorption is affected by electrostatic interaction and H-bonding (PE). Conversely, adsorption of PA involves phosphate inner-sphere complexes, for both goethite and hematite, via P-OFe bond formation. Biomolecule adsorption at the interface was observed to occur on the scale of minutes to hours. Exponential and linear increases in peak intensity were observed for goethite and hematite, respectively. Our ATR-FTIR results on the PA terminal phosphate are in good agreement with those on EPS reacted with goethite and on bacterial cell adhesion to hematite. These findings suggest that the plasma membrane, and the PA terminal phosphate in particular, may play a role in mediating the interaction between bacteria and iron oxide surfaces during initial stages of biofilm formation. © 2009 Elsevier B.V. All rights reserved.
• Francesconi, K. A., & Chorover, J. (2010). Recalcitrance-dead and buried?. Environmental Chemistry, 7(4), 319-.
• Gao, X., & Chorover, J. (2010). Adsorption of sodium dodecyl sulfate (SDS) at ZnSe and α-Fe₂O₃ surfaces: Combining infrared spectroscopy and batch uptake studies. Journal of Colloid and Interface Science, 348(1), 167-176.
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  PMID: 20472243;Abstract: Adsorption of sodium dodecyl sulfate (SDS) at the solid/aqueous interface was examined as a function of pH and SDS concentration ([SDS]) using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and batch uptake experiments. Two types of sorbent surfaces were compared: (i) a hydrophobic zinc selenide (ZnSe) ATR internal reflection element (IRE) and (ii) the same surface coated with hydrophilic nanoparticulate α-Fe2O3 (hematite). The results indicate that adsorption to the ZnSe IRE is affected by both electrostatic attraction and hydrophobic interaction. Batch adsorption and ATR-FTIR spectral results are consistent with SDS forming outer-sphere complexes at the α-Fe2O3 surface. There is also no evidence for ligand (SDS)-promoted dissolution of hematite. Adsorption to hematite is dominated by anion exchange and surfactant self-assembly. ATR-FTIR data indicate that adsorption to both surfaces shows a strong pH dependence at low [SDS] and negligible pH dependence when [SDS] exceeds the critical micelle concentration (cmc). Adsorption to ZnSe IRE shows small variation with [SDS], apparently due to a lack of surfactant self-assembly at the interface. Adsorption to α-Fe2O3 is a rapid process; equilibrium is reached within a few minutes. Conversely, adsorption to the ZnSe IRE shows strong longer time dependence; evidently, hydrophobic interfacial reactions constitute a much slower process. © 2010.
• Goyne, K. W., Brantley, S. L., & Chorover, J. (2010). Rare earth element release from phosphate minerals in the presence of organic acids. Chemical Geology, 278(1-2), 1-14.
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  Abstract: The primary objective of this research was to investigate the effects of aliphatic and aromatic low molecular weight organic acids (LMWOAs) on rare earth element and yttrium (REY) release from the phosphate minerals apatite and monazite. Since prior studies have shown that redox status can affect REY partitioning during incongruent dissolution, a secondary objective was to assess the influence of dissolved O2 concentration. Increasing LMWOA concentrations from 0 to 10mM resulted in enhanced REY release. In general, REY release increased in the order: no ligand≈salicylate
• Mikutta, R., Kaiser, K., Dörr, N., Vollmer, A., Chadwick, O. A., Chorover, J., Kramer, M. G., & Guggenberger, G. (2010). Mineralogical impact on organic nitrogen across a long-term soil chronosequence (0.3-4100 kyr). Geochimica et Cosmochimica Acta, 74(7), 2142-2164.
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  Abstract: Large portions of organic N (ON) in soil exist tightly associated with minerals. Mineral effects on the type of interactions, chemical composition, and stability of ON, however, are poorly understood. We investigated mineral-associated ON along a Hawaiian soil chronosequence (0.3-4100 kyr) formed in basaltic tephra under comparable climatic, topographic, and vegetation conditions. Mineral-organic associations were separated according to density (ρ > 1.6 g/cm3), characterized by X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge fine structure (NEXAFS) and analyzed for amino acid enantiomers and amino sugars. The 14C activity of mineral-bound OC was estimated by accelerator mass spectrometry. The close OC-ON relationship (r = 0.96) and XPS results suggest that ON exists incorporated in bulk mineral-bound OM and likely becomes associated with minerals as part of sorbing OM. The youngest site (0.3 kyr), with soils mainly composed of primary minerals (olivine, pyroxene, feldspar) and with little ON, contained the largest proportion of hydrolyzable amino sugars and amino acids but with a small share of acidic amino acids (aspartic acid, glutamic acid). In soils of the intermediate weathering stage (20-400 kyr), where poorly crystalline minerals and metal(hydroxide)-organic precipitates prevail, more mineral-associated ON was present, containing a smaller proportion of hydrolyzable amino sugars and amino acids due to the preferential accumulation of other OM components such as lignin-derived phenols. Acidic amino acids were more abundant, reflecting the strong association of acidic organic components with metal(hydroxide)-organic precipitates and variable-charge minerals. In the final weathering stage (1400-4100 kyr) with well-crystalline secondary Fe and Al (hydr)oxides and kaolin minerals, mineral-organic associations held less ON and were, relative to lignin phenols, depleted in hydrolyzable amino sugars and amino acids, particularly in acidic amino acids. XPS and NEXAFS analyses showed that the majority (59-78%) of the mineral-associated ON is peptide N while 18-34% was aromatic N. Amino sugar ratios and d-alanine suggest that mineral-associated ON comprises a significant portion of bacterial residues, particularly in the subsoil. With increasing 14C age, a larger portion of peptide N was non-hydrolyzable, suggesting the accumulation of refractory compounds with time. The constant d/l ratios of lysine in topsoils indicate fresh proteinous material, likely due to continuous sorption of or exchange with fresh N-containing compounds. The 14C and the d/l signature revealed a longer turnover of proteinous components strongly bound to minerals (not NaOH-NaF-extractable). This study provides evidence that interactions with minerals are important in the transformation and stabilization of soil ON. Mineral-associated ON in topsoils seems actively involved in the N cycling of the study ecosystems, accentuating N limitation at the 0.3-kyr site but increasing N availability at older sites. © 2010 Elsevier Ltd. All rights reserved.
• Mohanram, A., Ray, C., Harvey, R. W., Metge, D. W., Ryan, J. N., Chorover, J., & Eberl, D. D. (2010). Comparison of transport and attachment behaviors of Cryptosporidium parvum oocysts and oocyst-sized microspheres being advected through three minerologically different granular porous media. Water Research, 44(18), 5334-5344.
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  PMID: 20637489;Abstract: In order to gain more information about the fate of Cryptosporidium parvum oocysts in tropical volcanic soils, the transport and attachment behaviors of oocysts and oocyst-sized polystyrene microspheres were studied in the presence of two soils. These soils were chosen because of their differing chemical and physical properties, i.e., an organic-rich (43-46% by mass) volcanic ash-derived soil from the island of Hawaii, and a red, iron (22-29% by mass), aluminum (29-45% by mass), and clay-rich (68-76% by mass) volcanic soil from the island of Oahu. A third agricultural soil, an organic- (13% by mass) and quartz-rich (40% by mass) soil from Illinois, was included for reference. In 10-cm long flow-through columns, oocysts and microspheres advecting through the red volcanic soil were almost completely (98% and 99%) immobilized. The modest breakthrough resulted from preferential flow-path structure inadvertently created by soil-particle aggregation during the re-wetting process. Although a high (99%) removal of oocysts and microsphere within the volcanic ash soil occurred initially, further examination revealed that transport was merely retarded because of highly reversible interactions with grain surfaces. Judging from the slope of the substantive and protracted tail of the breakthrough curve for the 1.8-μm microspheres, almost all (>99%) predictably would be recovered within ~4000 pore volumes. This suggests that once contaminated, the volcanic ash soil could serve as a reservoir for subsequent contamination of groundwater, at least for pathogens of similar size or smaller. Because of the highly reversible nature of organic colloid immobilization in this soil type, C. parvum could contaminate surface water should overland flow during heavy precipitation events pick up near-surface grains to which they are attached. Surprisingly, oocyst and microsphere attachment to the reference soil from Illinois appeared to be at least as sensitive to changes in pH as was observed for the red, metal-oxide rich soil from Oahu. In contrast, colloidal attachment in the organic-rich, volcanic ash soil was relatively insensitive to changes in pH in spite of the high iron content. Given the fundamental differences in transport behavior of oocyst-sized colloids within the two volcanic soils of similar origin, agricultural practices modified to lessen C. parvum contamination of ground or surface water would necessitate taking the individual soil properties into account. © 2010.
• Thompson, A., Steefel, C. I., Perdrial, N., & Chorover, J. (2010). Contaminant desorption during long-term leaching of hydroxide-weathered hanford sediments. Environmental Science and Technology, 44(6), 1992-1997.
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  PMID: 20170202;Abstract: Mineral sorption/coprecipitation is thought to be a principal sequestration mechanism for radioactive 90Sr and 137Cs in sediments impacted by hyperalkaline, high-level radioactive waste (HLRW) at the DOE's Hanford site. However, the longterm persistence of neo-formed, contaminant bearing phases after removal of the HLRW source is unknown. We subjected pristine Hanford sediments to hyperalkaline Na-Al-NO3-OH solutions containing Sr, Cs, and I at 10-5,10-5, and 10-7 molal, respectively, for 182 days with either
• Thompson, A., Steefel, C. I., Perdrial, N., & Chorover, J. (2010). Erratum: Contaminant Desorption during Long-Term Leaching of Hydroxide-Weathered Sediments(Environmental Science and Technology (2010) 44 (4384)). Environmental Science and Technology, 44(11), 4384-.
• Dauer, J. M., Withington, J. M., Oleksyn, J., Chorover, J., Chadwick, O. A., Reich, P. B., & Eissenstat, D. M. (2009). A scanner-based approach to soil profile-wall mapping of root distribution. Dendrobiology, 62, 35-40.
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  Abstract: Root distribution sampling techniques are often inaccurate, time consuming and costly. We present an inexpensive approach to soil profile-wall mapping using a desktop scanner that allowed us to spend reduced time in the field. The scanner was pressed onto the vertical surface of a 1 × 1 m soil pit and images of the roots were taken in situ. In a common garden planting of eleven, 30-year-old conifer and hardwood tree species in Poland, we compared root counts (number of roots cm-2) obtained by this method with independent measurements of root length density (RLD) obtained from soil cores. We found a positive correlation (Spearman rank correlation r=0.93; P
• Dontsova, K. M., Steefel, C. I., Desilets, S., Thompson, A., & Chorover, J. D. (2009). Solid phase evolution in the Biosphere 2 hillslope experiment as predicted by modeling of hydrologic and geochemical fluxes. Hydrology and Earth System Sciences, 13(12), 2273-2286.
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  Abstract: A reactive transport geochemical modeling study was conducted to help predict the mineral transformations occurring over a ten year time-scale that are expected to impact soil hydraulic properties in the Biosphere 2 (B2) synthetic hillslope experiment. The modeling sought to predict the rate and extent of weathering of a granular basalt (selected for hillslope construction) as a function of climatic drivers, and to assess the feedback effects of such weathering processes on the hydraulic properties of the hillslope. Flow vectors were imported from HYDRUS into a reactive transport code, CrunchFlow2007, which was then used to model mineral weathering coupled to reactive solute transport. Associated particle size evolution was translated into changes in saturated hydraulic conductivity using Rosetta software. We found that flow characteristics, including velocity and saturation, strongly influenced the predicted extent of incongruent mineral weathering and neo-phase precipitation on the hillslope. Results were also highly sensitive to specific surface areas of the soil media, consistent with surface reaction controls on dissolution. Effects of fluid flow on weathering resulted in significant differences in the prediction of soil particle size distributions, which should feedback to alter hillslope hydraulic conductivities.
• Gao, X., & Chorover, J. (2009). In-situ monitoring of Cryptosporidium parvum oocyst surface adhesion using ATR-FTIR spectroscopy. Colloids and Surfaces B: Biointerfaces, 71(2), 169-176.
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  PMID: 19269797;Abstract: Surface chemistry and molecular interaction mechanisms of Cryptosporidium parvum oocysts with a ZnSe internal reflection element (IRE) surface were investigated as a function of pH and ionic strength in NaCl and CaCl2 background electrolyte using in-situ ATR-FTIR spectroscopy. Since the surface properties of oocysts play an important role in adhesion behavior, the effects of surface modifications that are commonly employed to inactivate the pathogen for laboratory studies, including viable (control), formalin-, and heat-inactivation, were also examined. The ATR-FTIR spectra of oocyst surfaces exhibit amide, carboxylate, phosphate, and polysaccharide functional groups. Results indicate that changes in solution chemistry strongly impact oocyst adhesion behavior in aqueous systems. Increasing ionic strength from 1 to 100 mM or decreasing pH from 9.0 to 3.0 resulted in an increase in oocyst adhesion to the IRE surface as measured by IR absorbance. For equivalent ionic strength, the adhesion rate was found to be independent of CaCl2 versus NaCl electrolyte solution, but was increased following formalin and heat treatments. This latter effect correlated with molecular changes reflected in spectral data. The ratio of amide I:amide II band intensities increased, and sugar ring vibrations at 1023 cm-1 became sharper and more intense following formalin treatment. Similar changes in the polysaccharide region were observed following heat treatment, and protein secondary structure was also altered from mainly parallel β-sheet to anti-parallel β-sheet conformation. © 2009 Elsevier B.V. All rights reserved.
• Gao, X., Metge, D. W., Ray, C., Harvey, R. W., & Chorover, J. (2009). Surface complexation of carboxylate adheres Cryptosporidium parvum oocysts to the hematite-water interface. Environmental Science and Technology, 43(19), 7423-7429.
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  PMID: 19848156;Abstract: The interaction of viable Cryptosporidium parvum öocysts at the hematite (α-Fe2O3)-water interface was examined over a wide range in solution chemistry using in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Spectra for hematite-sorbed öocysts showed distinctchangesin carboxylate group vibrations relative to spectra obtained in the absence of hematite, indicative of direct chemical bonding between carboxylate groups and Fe metal centers of the hematite surface. The data also indicate that complexation modes vary with solution chemistry. In NaCl solution, öocysts are bound to hematite via monodentate and binuclear bidentate complexes. The former predominates at low pH, whereas the latter becomes increasingly prevalent with increasing pH. In a CaCl2 solution, only binuclear bidentate complexes are observed. When solution pH is above the point of zero net proton charge (PZNPC) of hematite, öocyst surface carboxylate groups are bound to the mineral surface via outer-sphere complexes in both electrolyte solutions. © 2009 American Chemical Society.
• Mikutta, R., Schaumann, G. E., Gildemeister, D., Bonneville, S., Kramer, M. G., Chorover, J., Chadwick, O. A., & Guggenberger, G. (2009). Biogeochemistry of mineral-organic associations across a long-term mineralogical soil gradient (0.3-4100 kyr), Hawaiian Islands. Geochimica et Cosmochimica Acta, 73(7), 2034-2060.
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  Abstract: Organic matter (OM) in mineral-organic associations (MOAs) represents a large fraction of carbon in terrestrial ecosystems which is considered stable against biodegradation. To assess the role of MOAs in carbon cycling, there is a need to better understand (i) the time-dependent biogeochemical evolution of MOAs in soil, (ii) the effect of the mineral composition on the physico-chemical properties of attached OM, and (iii) the resulting consequences for the stabilization of OM. We studied the development of MOAs across a mineralogical soil gradient (0.3-4100 kyr) at the Hawaiian Islands that derived from basaltic tephra under comparable climatic and hydrological regimes. Mineral-organic associations were characterized using biomarker analyses of OM with chemolytic methods (lignin phenols, non-cellulosic carbohydrates) and wet chemical extractions, surface area/porosity measurements (N2 at 77 K and CO2 at 273 K), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The results show that in the initial weathering stage (0.3 kyr), MOAs are mainly composed of primary, low-surface area minerals (olivine, pyroxene, feldspar) with small amounts of attached OM and lignin phenols but a large contribution of microbial-derived carbohydrates. As high-surface area, poorly crystalline (PC) minerals increase in abundance during the second weathering stage (20-400 kyr), the content of mineral-associated OM increased sharply, up to 290 mg C/g MOA, with lignin phenols being favored over carbohydrates in the association with minerals. In the third and final weathering stage (1400-4100 kyr), metastable PC phases transformed into well crystalline secondary Fe and Al (hydr)oxides and kaolin minerals that were associated with less OM overall, and depleted in both lignin and carbohydrate as a fraction of total OM. XPS, the N2 pore volume data and OM-mineral volumetric ratios suggest that, in contrast to the endmember sites where OM accumulated at the surfaces of larger mineral grains, topsoil MOAs of the 20-400-kyr sites are composed of a homogeneous admixture of small-sized PC minerals and OM, which originated from both adsorption and precipitation processes. The chemical composition of OM in surface-horizon MOAs, however, was largely controlled by the uniform source vegetation irrespective of the substrate age whereas in subsoil horizons, aromatic and carboxylic C correlated positively with oxalate-extractable Al and Si and CuCl2-extractable Al concentrations representing PC aluminosilicates and Al-organic complexes (r2 > 0.85). Additionally, XPS depth profiles suggest a zonal structure of sorbed OM with aromatic carbons being enriched in the proximity of mineral surfaces and amide carbons (peptides/proteins) being located in outer regions of MOAs. Albeit the mineralogical and compositional changes of OM, the rigidity of mineral-associated OM as analyzed by DSC changed little over time. A significantly reduced side chain mobility of sorbed OM was, however, observed in subsoil MOAs, which likely arose from stronger mineral-organic bindings. In conclusion, our study shows that the properties of soil MOAs change substantially over time with different mineral assemblages favoring the association of different types of OM, which is further accentuated by a vertical gradient of OM composition on mineral surfaces. Factors supporting the stabilization of sorbed OM were (i) the surface area and reactivity of minerals (primary or secondary crystalline minerals versus PC secondary minerals), (ii) the association of OM with micropores of PC minerals (via 'sterically' enhanced adsorption), (iii) the effective embedding of OM in 'well mixed' arrays with PC minerals and monomeric/polymeric metal species, (iv) the inherent stability of acidic aromatic OM components, and (iv) an impaired segmental mobility of sorbed OM, which might increase its stability against desorption and microbial utilization. © 2009 Elsevier Ltd. All rights reserved.
• Chorover, J., Choi, S., Rotenberg, P., Serne, R. J., Rivera, N., Strepka, C., Thompson, A., Mueller, K. T., & O'Day, P. A. (2008). Silicon control of strontium and cesium partitioning in hydroxide-weathered sediments. Geochimica et Cosmochimica Acta, 72(8), 2024-2047.
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  Abstract: Cation partitioning and speciation in an aqueous soil suspension may depend on the coupling of reaction time, sorbate amount and mineral weathering reactions. These factors were varied in sediment suspension experiments to identify geochemical processes that affect migration of Sr2+ and Cs+ introduced to the subsurface by caustic high level radioactive waste (HLRW). Three glacio-fluvial and lacustrine sediments from the Hanford Site (WA, USA) were subjected to hyperalkaline (pH > 13), Na-Al-NO3-OH solution conditions within a gradient field of (i) sorptive concentration (10-5-10-3 m) and (ii) reaction time (0-365 d). Strontium uptake (qSr) exceeded that of cesium at nearly all reaction times. Sorbent affinity for both Cs+ and Sr2+ increased with clay plus silt content at early times, but a prolonged slow uptake process was observed over the course of sediment weathering that erased the texture effect for Sr2+; all sediments showed similar mass normalized uptake after several months of reaction time. Strontium became progressively recalcitrant to desorption after 92 d, with accumulation and aging of neoformed aluminosilicates. Formation of Cs+ and Sr2+-containing cancrinite and sodalite was observed after 183 d by SEM and synchrotron μ-XRF and μ-XRD. EXAFS data for qSr ≈ 40 mmol kg-1 showed incorporation of Sr2+ into both feldspathoid and SrCO3(s) coordination environments after one year. Adsorption was predominant at early times and low sorbate amount, whereas precipitation, controlled largely by sediment Si release, became increasingly important at longer times and higher sorbate amount. Kinetics of contaminant desorption at pH 8 from one year-weathered sediments showed significant dependence on background cation (Ca2+ versus K+) composition. Results of this study indicate that co-precipitation and ion exchange in neoformed aluminosilicates may be an important mechanism controlling Sr2+ and Cs+ mobility in siliceous sediments impacted by hyperalkaline HLRW. © 2008 Elsevier Ltd. All rights reserved.
• Davidson, E. A., Dail, D. B., & Chorover, J. (2008). Iron interference in the quantification of nitrate in soil extracts and its effect on hypothesized abiotic immobilization of nitrate. Biogeochemistry, 90(1), 65-73.
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  Abstract: Human alteration of the nitrogen cycle has stimulated research on nitrogen cycling in many aquatic and terrestrial ecosystems, where analyses of nitrate (NO3-) by standard laboratory methods are common. A recent study by Colman et al. (Biogeochemistry 84:161-169, 2007) identified a potential analytical interference of soluble iron (Fe) with NO3- quantification by standard flow-injection analysis of soil extracts, and suggested that this interference may have led Dail et al. (Biogeochemistry 54:131-146, 2001) to make an erroneous assessment of abiotic nitrate immobilization in prior 15N pool dilution studies of Harvard Forest soils. In this paper, we reproduce the Fe interference problem systematically and show that it is likely related to dissolved, complexed-Fe interfering with the colorimetric analysis of NO2-. We also show how standard additions of NO3- and NO 2- to soil extracts at native dissolved Fe concentrations reveal when the Fe interference problem occurs, and permit the assessment of its significance for past, present, and future analyses. We demonstrate low soluble Fe concentrations and good recovery of standard additions of NO 3- and NO2- in extracts of sterilized Harvard Forest soils. Hence, we maintain that rapid NO3- immobilization occurred in sterilized samples of the Harvard Forest O horizon in the study by Dail et al. (2001). Furthermore, additional evidence is accumulating in the literature for rapid disappearance of NO3- added to soils, suggesting that our observations were not the result of an isolated analytical artifact. The conditions for NO3- reduction are likely to be highly dependent on microsite properties, both in situ and in the laboratory. The so-called "ferrous wheel hypothesis" (Davidson et al., Glob Chang Biol 9:228-236, 2003) remains an unproven, viable explanation for published observations. © 2008 Springer Science+Business Media B.V.
• Hartemink, A. E., Chorover, J., & McBratney, A. B. (2008). Discussion papers. Geoderma, 144(3-4), 416-417.
• Parikh, S. J., & Chorover, J. (2008). ATR-FTIR study of lipopolysaccharides at mineral surfaces. Colloids and Surfaces B: Biointerfaces, 62(2), 188-198.
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  PMID: 18006288;Abstract: Lipopolysaccharides (LPS) are ubiquitous in natural aqueous systems because of bacterial cell turnover and lysis. LPS sorption and conformation at the mineral/water interface are strongly influenced by both solution and surface chemistry. In this study, the interaction of LPS with various surfaces (ZnSe, GeO2, α-Fe2O3, α-Al2O3) that vary in surface charge and hydrophobicity was investigated using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The presence of Ca2+ (versus Na+) in LPS solutions resulted in aggregate reorientation and increased sorptive retention. ATR-FTIR spectra of Na-LPS systems are consistent with reduced surface affinity and are similar to those of solution phase LPS. Ca-LPS spectra reveal hydrophobic interactions of the lipid A region at the ZnSe internal reflection element (IRE). However, pH-dependent charge controls Ca-LPS sorption to hydrophilic surfaces (GeO2, α-Fe2O3, and α-Al2O3), where bonding occurs principally via O-antigen functional groups. As a result of accumulation at the solid-liquid interface, spectra of Ca-LPS represent primarily surface-bound LPS. Variable-angle ATR-FTIR spectra of Ca-LPS systems show depth-dependent trends that occur at the spatial scale of LPS aggregates, consistent with the formation of vesicular structures.
• Chorover, J., Kraemer, S., Cervini-Silva, J., & Maurice, P. (2007). Physical chemistry of soils and aquifers: A special issue in honor of Garrison Sposito. Geochimica et Cosmochimica Acta, 71(23), 5579-5582.
• Chorover, J., Kretzschmar, R., Garica-Pichel, F., & Sparks, D. L. (2007). Soil biogeochemicial processes within the critical zone. Elements, 3(5), 321-326.
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  Abstract: Many processes that affect soil and water quality occur at the water-wetted interface of weathering products such as clays, oxides, and organic matter. Especially near the sunlit surface of the Critical Zone, these interfaces associate with plant roots and soil organisms to form porous, aggregated structures. Soil aggregates and intervening pore networks give rise to a patchwork of interconnected microenvironments. The ensuing steep geochemical gradients affect weathering processes, fuel the activities of microbes, and drive interfacial reactions that retain and transform rock- or ecosystem-derived chemicals and anthropogenic pollutants.
• Dauer, J. M., Chorover, J., Chadwick, O. A., Oleksyn, J., Tjoelker, M. G., Hobbie, S. E., Reich, P. B., & Eissenstat, D. M. (2007). Controls over leaf and litter calcium concentrations among temperate trees. Biogeochemistry, 86(2), 175-187.
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  Abstract: Four-fold variation in leaf-litter Ca concentration among 14 tree species growing in a common garden in central Poland was linked to variation in soil pH, exchangeable Ca, soil base saturation, forest floor turnover rates, and earthworm abundance. Given the potential importance of tissue Ca to biogeochemical processes, in this study we investigated potential controls on leaf Ca concentrations using studies of both laboratory seedlings and 30-year-old trees in the field. We first assessed whether species differences in Ca concentration of green leaves and leaf litter were due to differences in Ca uptake, plant growth, or Ca translocation to different organs, by measuring seedlings of 6 of the 14 species grown under controlled conditions of varying Ca supply. We also investigated whether trees species with high Ca concentrations in green leaves and leaf litter access soil Ca to a greater extent than low-Ca species by growing more fine roots in high-Ca soil horizons. Root distribution in the field was determined in all 14 tree species by profile wall mapping and soil sampling of excavated pits. There was no correlation between horizon root count density (number of roots m-2) and exchangeable soil Ca, nor was there a correlation of stand-level leaf litter Ca with density of roots 45-100 cm deep in the soil, suggesting that a deeper root distribution does not result in greater Ca acquisition among these species. Variation among species in leaf Ca concentration of greenhouse seedlings was positively correlated with leaf Ca concentrations of mature trees, indicating that the same ranking in leaf Ca among species existed under controlled Ca supply. Species also differed in seedling growth response to Ca supply. Tilia, the species with the highest leaf Ca in the field, generated only 10% as much biomass and height at low relative to high Ca supply, whereas the other species exhibited no significant differences. Species exhibited differences in (i) partitioning of whole plant Ca and biomass to leaf, stem and root organs and (ii) the pattern of such partitioning between high and low Ca treatments. Our data support the hypothesis that although soil Ca supply can contribute to variation among trees in leaf and litter Ca concentration, innate physiological differences among species also can be a major cause for species variation. © 2007 Springer Science+Business Media B.V.
• Hobbie, S. E., Ogdahl, M., Chorover, J., Chadwick, O. A., Oleksyn, J., Zytkowiak, R., & Reich, P. B. (2007). Tree species effects on soil organic matter dynamics: The role of soil cation composition. Ecosystems, 10(6), 999-1018.
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  Abstract: We studied the influence of tree species on soil carbon and nitrogen (N) dynamics in a common garden of replicated monocultures of fourteen angiosperm and gymnosperm, broadleaf and needleleaf species in southwestern Poland. We hypothesized that species would influence soil organic matter (SOM) decomposition primarily via effects on biogeochemical recalcitrance, with species having tissues with high lignin concentrations retarding rates of decomposition in the O and A horizons. Additionally, because prior work demonstrated substantial divergence in foliar and soil base cation concentrations and soil pH among species, we hypothesized that species would influence chemical stabilization of SOM via cation bridging to mineral surfaces in the A-horizon. Our hypotheses were only partially supported: SOM decomposition and microbial biomass were unrelated to plant tissue lignin concentrations, but in the mineral horizon, were significantly negatively related to the percentage of the cation exchange complex (CEC) occupied by polyvalent acidic (hydrolyzing) cations (Al and Fe), likely because these cations stabilize SOM via cation bridging and flocculation and/or because of inhibitory effects of Al or low pH on decomposers. Percent CEC occupied by exchangeable Al and Fe was in turn related to both soil clay content (a parent material characteristic) and root Ca concentrations (a species characteristic). In contrast, species influenced soil N dynamics largely via variation in tissue N concentration. In both laboratory and in situ assays, species having high-N roots exhibited faster rates of net N mineralization and nitrification. Nitrification:mineralization ratios were greater, though, under species with high exchangeable soil Ca2+. Our results indicate that tree species contribute to variation in SOM dynamics, even in the mineral soil horizons. To our knowledge the influence of tree species on SOM decomposition via cation biogeochemistry has not been demonstrated previously, but could be important in other poorly buffered systems dominated by tree species that differ in cation nutrition or that are influenced by acidic deposition. © 2007 Springer Science+Business Media, LLC.
• Ohno, T., Chorover, J., Omoike, A., & Hunt, J. (2007). Molecular weight and humification index as predictors of adsorption for plant- and manure-derived dissolved organic matter to goethite. European Journal of Soil Science, 58(1), 125-132.
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  Abstract: Sorptive retention of organic matter is important in maintaining the fertility and quality of soils in agricultural ecosystems. However, few sorption studies have been conducted that use dissolved organic matter (DOM) characteristic of agricultural amendments. We investigated the sorption to goethite (α-FeOOH) of DOM extracted from: (i) above-ground biomass of wheat straw (Triticum aestivum L.), maize residue (Zea mays L.), soybean residue (Glycine max (L.) Merr.), and hairy vetch residue (Vivia billosa L.); (ii) below-ground biomass from maize, soybean, canola (Brassica napus L.), and green bean (Phaseolus vulgaris L.); and (iii) beef, dairy, poultry, and pig animal manures. The apparent molecular weight (MWAP) of the DOM was measured by high performance-size exclusion chromatography and ranged from 312 to 1074 g mol-1. The carboxyl-group content of the DOM measured by potentiometric titration ranged from 4.84 to 21.38 mmol(-) g -1 carbon. The humification index (HIX) determined by fluorescence spectrometry varied from 1.15 to 4.33. Sorption was directly related to both MWAP and HIX values of the DOM. Molecular weight analysis of the solution prior to and after sorption indicated that the DOM molecules > 1800 g mol-1 were preferentially sorbed, resulting in fractionation of the DOM upon reaction with goethite. The multiple regression equation, based only on MWAP and HIX parameters, explained 76% of the variance in amount of DOM sorbed. The results indicate that MWAP and HIX are important factors in controlling the sorption of DOM to mineral surfaces. Amendment with materials that release DOM of higher molecular weight and greater humification will result in enhanced initial sorption of DOM to soil solids, thereby contributing to accumulation of a larger soil organic C pool. © 2006 British Society of Soil Science.
• Parikh, S. J., & Chorover, J. (2007). Infrared spectroscopy studies of cation effects on lipopolysaccharides in aqueous solution. Colloids and Surfaces B: Biointerfaces, 55(2), 241-250.
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  PMID: 17275267;Abstract: The conformation of amphiphilic lipopolysaccharides (LPS) influences the behavior of free and cell-bound LPS in aqueous environments, including their adhesion to surfaces. Conformational changes in Pseudomonas aeruginosa serotype 10 LPS aggregates resulting from changes in solution pH (3, 6, and 9), ionic strength [I] 1, 10, and 100 mmol L-1, and electrolyte composition (NaCl and CaCl2) were investigated via attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy. ATR-FTIR data indicate that LPS forms more stable aggregates in NaCl relative to CaCl2 solutions. Time- and cation-dependent changes in ATR-FTIR data suggest that LPS aggregates are perturbed by Ca2+ complexation at lipid A phosphoryl groups, which leads to reorientation of the lipid A at the surface of a ZnSe ATR internal reflection element (IRE). Polarized ATR-FTIR investigations reveal orientation of LPS dipoles approximately perpendicular to the IRE plane for both Na- and Ca-LPS. The results indicate that changes in solution chemistry strongly impact the conformation, intermolecular and interfacial behavior of LPS in aqueous systems. © 2007 Elsevier B.V. All rights reserved.
• Thompson, A., Ruiz, J., Chadwick, O. A., Titus, M., & Chorover, J. (2007). Rayleigh fractionation of iron isotopes during pedogenesis along a climate sequence of Hawaiian basalt. Chemical Geology, 238(1-2), 72-83.
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  Abstract: We measured iron isotopic composition of surface (10-20 cm) and subsurface (50-70 cm) basaltic soil horizons from the Island of Maui along a climate gradient (MCG) ranging from 2.2 to 4.2 m mean annual precipitation (MAP). All soil forming factors except climate were conserved. The MCG has a documented decrease in Fe with increasing rainfall that is highly correlated with decreasing mean annual Eh values. We found that increasing MAP from 2.8 to 4.2 m resulted in a surface plus subsurface average increase of 0.56‰ ± 0.09‰ δ56Fe with the subsurface consistently 0.33 ± 0.06‰ δ56Fe greater than the surface horizons. Based on loss of Fe relative to Nb, Rayleigh fractionation was observed with 103lnαlost-retained values of - 0.37 ± 0.03 and - 0.34 ± 0.04 for the surface and subsurface, respectively. Equivalent 103lnαlost-retained values for the surface and subsurface soils suggests Fe loss is driven by similar mechanisms throughout the soil profile. Our calculated fractionation factor is about 1/3 the magnitude of laboratory determined fractionation factors for Fe reduction, suggesting other processes (organic complexation, Fe re-precipitation) modulate the net Fe loss along the MCG. These results offer field-scale confirmation of laboratory experiments on model systems that show anoxic weathering reactions produce materials enriched in heavy Fe isotopes. © 2006 Elsevier B.V. All rights reserved.
• Chefetz, B., Ilani, T., Schulz, E., & Chorover, J. (2006). Wastewater dissolved organic matter: Characteristics and sorptive capabilities. Water Science and Technology, 53(7), 51-57.
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  PMID: 16752764;Abstract: An evaluation of the mobility of organic pollutants with wastewater dissolved organic matter (DOM) is essential to better understanding their fate and toxicity to the environment. In this study, DOM from two wastewater treatment plants (in Lachish and Netanya, Israel) were fractionated to hydrophobic-acid (HoA) and hydrophobic-neutral (HoN) fractions. The fractions were characterised and their sorptive capabilities for s-triazine herbicides and polycyclic aromatic hydrocarbons (PAHs) were studied. For all sorbates, binding to the HoN fractions was much higher than to HoA fractions. The high binding coefficients obtained for the studied triazines by the HoN fractions suggested that their sorption is governed by hydrophobic-like interactions rather than H-bonding. The binding coefficients of PAHs measured for the HoN fractions were within the range reported for humic acids and much higher than for the HoA fraction, suggesting that the HoN fraction plays an important role in the overall sorption of these compounds by DOM. Higher sorption coefficients were measured for the Netanya DOM sample containing a higher level of hydrophobic fractions (HoA + HoN) than the Lachish DOM, suggesting that the sorption of hydrophobic organic compounds by DOM is governed by the relative content of these structural substances. © IWA Publishing 2006.
• Crosson, C. S., Choi, S., Chorover, J., Amistadi, M. K., O'Day, P. A., & Mueller, K. T. (2006). Solid-state NMR identification and quantification of newly formed aluminosilicate phases in weathered kaolinite systems. Journal of Physical Chemistry B, 110(2), 723-732.
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  PMID: 16471594;Abstract: The weathering of a specimen kaolinite clay was studied over the course of 369 d via solid-state 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and high-field 27Al MAS NMR. The chosen baseline solution conditions (0.05 mol kg -1 of Al, 2 mol kg -1 of Na +, 1 mol kg -1 of NO 3-, 1 mol kg -1 of OH -, and pH ∼13.8) approximate those of solutions leaking from waste tanks at the Hanford Site in Richland, WA. Nonradioactive Cs and Sr cations were added to this synthetic tank waste leachate (STWL) solution at concentrations of 10 -3, 10 -4, and 10 -5 molal (m) to represent their radionuclide counterparts. The transformations of silicon- and aluminum-containing solid phase species were monitored quantitatively by using NMR spectroscopy, with the resulting spectra directly reporting the influence of the initial Cs and Sr on formation and transformation of the neo-formed solids. At the lowest concentration of Cs and Sr employed (10 -5 m in each cation) peaks consistent with the formation of zeolite-like minerals were detected via 29Si and 27Al MAS NMR as early as 33 d. At concentrations of 10 -3 m in each cation, new silicon species are not detected until 93 d, although neophases containing four-coordinate aluminum were detectable at earlier reaction times via 27Al MAS NMR. At the highest magnetic field strengths employed in this NMR study, deconvolutions of resonances detected in the tetrahedral region of the 27Al MAS spectra yielded multiple components, indicating the existence of at least four new aluminum-containing phases. Two of these phases are identified as sodalite and cancrinite through comparison with diffuse-reflectance infrared (DRIFT) spectra and powder X-ray diffraction (XRD) results, while a third phase may correlate with a previously detected aluminum-rich chabazite phase. All measurable solid reaction products have been quantified via their 27Al MAS resonances acquired at high magnetic field strengths (17.6 T), and the quantitative nature of the 27Al NMR data shows that cancrinite growth increases while sodalite reaches a steady state with respect to total aluminum in the solid phases. The data also relate the coupling of Cs sorption to the ripening of feldspathoid phases in this heterogeneous system as a function of time, and illustrate the important influence of co-contaminants on the environmental reaction kinetics studied here. © 2006 American Chemical Society.
• Goyne, K. W., Brantley, S. L., & Chorover, J. (2006). Effects of organic acids and dissolved oxygen on apatite and chalcopyrite dissolution: Implications for using elements as organomarkers and oxymarkers. Chemical Geology, 234(1-2), 28-45.
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  Abstract: We have previously suggested that mobility patterns of P and Y in paleosols could serve as "organomarkers" to denote the presence of organic ligands secreted by terrestrial organisms on early Earth. In addition, our data indicate that Cu depletion may provide a viable oxymarker for determining the presence of atmospheric oxygen during soil weathering processes. In this research, we continue pursuing the potential for utilizing these elements as markers by investigating dissolution of Durango apatite (Ca5(PO4)2.82(F,Cl,OH)1.54) and Messina chalcopyrite (CuFeS2) reacted under batch conditions in the presence and absence of two aliphatic and aromatic organic acids under oxic and anoxic conditions. In general, results show that organic acids enhance element release from apatite (Ca, P and Y) and chalcopyrite (Cu, Fe, and Y), and increasing organic acid concentrations from 1 to 10 mM results in greater dissolution. The aliphatic organic acid citrate enhances mineral dissolution to the greatest extent and dissolution in the presence of aromatic salicylate or absence of ligand is lowest. Release of Ca, P, and Y from apatite was not impacted by dissolved O2(g) while release of Cu from chalcopyrite was impacted. Aqueous Cu concentrations at the end of batch experiments with chalcopyrite are four orders of magnitude greater under oxic conditions, whereas Fe concentrations are substantially higher under anoxic conditions. These data support the hypothesis that release of P and Y from apatite is enhanced by organic acids and that Cu release is impacted significantly by dissolved O2(g) and, to a lesser extent, organic acids. Thus, it seems plausible that geochemical and mineralogical signatures of P, Y, and Cu may have utility for distinguishing the presence of terrestrial organisms and atmospheric conditions during soil weathering processes on early Earth. © 2006 Elsevier B.V. All rights reserved.
• Guo, M., & Chorover, J. (2006). Leachate migration from spent mushroom substrate through intact and repacked subsurface soil columns. Waste Management, 26(2), 133-140.
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  PMID: 16310116;Abstract: Field weathering of spent mushroom substrate (SMS) produces soluble compost leachate that percolates into underlying soils and may adversely impact groundwater. Laboratory experiments were conducted to investigate movement and retention of SMS leachate solutes in subsurface soil columns. Spent mushroom substrate leachate with high concentrations of dissolved organic matter (DOM) and inorganic salts was passively loaded to intact and repacked columns of Bt1 soil (fine-loamy, mixed, semiactive, mesic Typic Hapludults) and effluents were monitored for changes in chemical composition. Transport of SMS leachate in undisturbed soil cores was mainly via preferential flow, whereas matrix flow was predominant in repacked soil columns. Leachate DOM and phosphate were sorbed by soil minerals while Cl-, SO42-, Na+ and NH4+ were eluted. Leachate K+ displaced exchangeable native cations and was retained. Biodegradation of leachate DOM resulted in reduction and elution of soil Mn and Fe, especially in repacked columns. Persistent anoxia also inhibited nitrification. Precipitation of gypsum and CaCO3 blocked preferential flow channels, and movement of SMS leachate was subsequently reduced. The results demonstrate that SMS leachate migrates via rapid preferential flow initially, followed by matrix flow at a lower rate. Leachate solutes may transport to depth in soil profiles through preferential channels. To protect water resources, weathering of deep SMS piles should be conducted on compact surfaces or in fields with a condensed soil layer (no structural cracks) above the groundwater table, and measures controlling leachate runoff be imposed. © 2005 Elsevier Ltd. All rights reserved.
• Neaman, A., Chorover, J., & Brantley, S. L. (2006). Effects of organic ligands on granite dissolution in batch experiments at pH 6. American Journal of Science, 306(6), 451-473.
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  Abstract: Yosemite granite from the Tuolumne River series was dissolved under oxic and anoxic conditions in the presence (0.001 or 0.01 M) and absence of organic ligands in batch experiments at pH 6. Release of all elements was enhanced considerably in the presence of organic ligands. Citrate (tridentate) and gallate (tetradentate) increased element release to the greatest extent among the aliphatic and aromatic ligands, respectively. The extent of element mobilization observed for the aliphatic ligands decreased in the order citrate > oxalate ≈ malonate and for the aromatic ligands gallate > salicylate ≈ phthalate. The effects of the ligands generally followed trends in cation-ligand stability constants, but aromatic ligands were less effective in element mobilization than aliphatic ligands. This was attributed to protonation of the functional groups of aromatic ligands at pH 6. Rock dissolution was non-stoichiometric regardless of the presence or absence of organic ligands. Release of P and Cu (% of total element content in the unweathered rock) in the presence of organic ligands was considerably greater than that of other elements. Findings of the present study were compared to the findings of our previous study on dissolution of basalt. Differences in the mobility patterns of Y, Fe, Cu, Ti, and Zr during dissolution of granite and basalt were observed. In basalt, release of Y was enhanced considerably in the presence of citrate. In contrast, in the present study, release of Y from granite with and without citrate was at the detection limit. This difference was attributed to the difference in Y-hosting parent minerals: apatite (basalt) and sphene (granite). With and without organic ligands, no significant differences were observed in the extent of Fe released from granite under oxic versus anoxic conditions, while the extent of Fe release from basalt was considerably greater under anoxic versus oxic conditions with and without organic ligands. These differences can be attributed to the difference in major Fe-hosting phases in the rocks: biotite (granite) versus glass and augite (basalt). In the granite, concentrations of Cu released increased considerably in the presence of organic ligands under both oxic and anoxic conditions. In contrast, concentrations of Cu released from basalt were increased considerably only under oxic conditions, especially in the presence of organic ligands. This difference was attributed to the different extent of Fe release from basalt and granite that affected dissolution of Cu/Fe-sulfides. Although both Ti and Zr can be mobilized in the presence of organic ligands, in the rock where zircons hosted Zr (granite), this element was the most immobile, while in the rock where Fe/Ti oxides hosted Zr (basalt), Ti was the most immobile.
• Omoike, A., & Chorover, J. (2006). Adsorption to goethite of extracellular polymeric substances from Bacillus subtilis. Geochimica et Cosmochimica Acta, 70(4), 827-838.
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  Abstract: Adsorption to goethite of extracellular polymeric substances from Bacillus subtilis Extracellular polymeric substances (EPS) are heterogeneous biopolymers produced by Gram-negative and Gram-positive bacterial cells. Adsorption of EPS to minerals can alter the substrata physico-chemistry and influence initial bacterial adhesion processes via conditioning film formation, but the effects of solution chemistry on uptake of EPS remain poorly understood. In this study, the adsorption to goethite (α-FeOOH) of EPS isolated from the early stationary growth-phase culture of Bacillus subtilis was investigated as a function of pH and ionic strength (I) in NaCl background electrolyte using batch studies coupled with Fourier transform infrared spectroscopy and size-exclusion high-performance liquid chromatography. Proteins, particularly those of higher molar mass, and phosphorylated macromolecules were adsorbed preferentially. Increasing solution I (1-100 mM NaCl) or pH (3.0-9.0) resulted in a decrease in the mass of EPS adsorbed. Batch studies and diffuse reflectance infrared Fourier transform spectra are consistent with ligand exchange of EPS phosphate groups for surface hydroxyls at Fe metal centers. The data indicate that both electrostatic and chemical bonding interactions contribute to selective fractionation of the EPS solution. Proteins and phosphate groups in phosphodiester bridges of nucleic acids likely play an important role in conditioning film formation at Fe oxide surfaces. © 2005 Elsevier Inc. All rights reserved.
• Parikh, S. J., & Chorover, J. (2006). ATR-FTIR spectroscopy reveals bond formation during bacterial adhesion to iron oxide. Langmuir, 22(20), 8492-8500.
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  PMID: 16981768;Abstract: The contribution of various bacterial surface functional groups to adhesion at hematite and ZnSe surfaces was examined using attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy. When live Shewanella oneidensis, Pseudomonas aeruginosa, and Bacillus subtilis cells were introduced to a horizontal hematite (α-Fe2O3)coated internal reflection element (IRE), FTIR peaks emerged corresponding to bacterial phosphate group binding. These IR peaks were not observed when bacteria were introduced to the uncoated ZnSe IRE. When cells were added to colloidal suspensions of α-Fe2O3 at pH 7, spectra included peaks corresponding to P-OFe and v(COOH), the latter being attributed to bridging of carboxylate at mineral surface OH groups. Selected model organic compounds with P-containing functionalities (phenylphosphonic acid [PPA], adenosine 5′-monophosphate [AMP], 2′-deoxyadenyl- (3′→5′)-2′-deoxyadenosine [DADA], and deoxyribonucleic acid [DNA]) produce spectra with similar peaks corresponding to P-OFe when adsorbed to α-Fe2O3. The data indicate that both terminal phosphate/phosphonate and phosphodiester groups, either exuded from the cell or present as surface biomolecules, are involved in bacterial adhesion to Fe-oxides through formation of innersphere Fe-phosphate/phosphonate complexes. © 2006 American Chemical Society.
• Thompson, A., Chadwick, O. A., Boman, S., & Chorover, J. (2006). Colloid mobilization during soil iron redox oscillations. Environmental Science and Technology, 40(18), 5743-5749.
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  PMID: 17007135;Abstract: In redox-dynamic soils, iron reduction-oxidation events may initiate wide shifts in the concentration of colloidal and dissolved material because of either Fe mineral dissolution or pH shifts associated with Fe oxidation state changes. This can have profound effects on the mobilization of organic and metal constituents. We conducted laboratory studies of colloid dynamics in a Hawaiian soil subjected to four consecutive 14-day reduction-oxidation cycles across the "soil-Fe" (Fe(OH)3)/(Fe2+(aq)) equilibrium. Size fractionated samples were isolated by differential centrifugation and characterized based on analysis of the framework and trace elements (Si, C, Fe, Ti, Al, Zr, Nb, La, and U). Intracycle oscillations in all colloidal (3 kDa to 160 nm) elements peaked during the reduction half-cycles, mobilizing 10% of total soil Ti and from 1-5% of total soil Zr, Nb, La, and U at peak dispersion. Colloid dynamics were dependent on pH shifts accompanying the redox oscillations rather than the fluctuating solubility of Fe oxides. TEM/EDS and mass-balance calculations suggest a carbon-based colloid matrix with zones of metal enrichment. The cumulative effects of four redox cycles included an apparent increase in colloid stability. Proton production/consumption associated with Fe-redox cycling has important implications for mobilization colloid-borne trace elements and sorbed contaminants. © 2006 American Chemical Society.
• Thompson, A., Chadwick, O. A., Rancourt, D. G., & Chorover, J. (2006). Iron-oxide crystallinity increases during soil redox oscillations. Geochimica et Cosmochimica Acta, 70(7), 1710-1727.
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  Abstract: An Inceptisol A-horizon from Hawaii was subjected to a series of reduction-oxidation cycles - 14 d cycle length over a 56 d duration - across the "soil-Fe" [Fe(OH)3.Fe2+(aq), log Ko = 15.74] equilibrium in triplicate redox-stat reactors. Each reducing event simulated the flush of organic C and diminished O2 that accompanies a rainfall-induced leaching of bioavailable reductants from the forest floor into mineral soil. The soil contained considerable amounts of short-range ordered (SRO) minerals (e.g., nano-goethite and allophane) and organic matter (11% org-C). Room temperature and cryogenic 57Fe Mössbauer spectroscopy showed that the iron-bearing minerals were dominated by nano- to micro-scale goethite, and that ferrihydrite was not present. Over the four full cycles, fluctuations in Eh (from 200 to 700 mV) and pFe2+ (from 2.5 to 5.5) were inversely correlated with those of pH (5.5 to 4). Here, we focus on the solubility dynamics of the framework elements (Si, Fe, Ti, and Al) that constitute 35% of the oxygen-free soil dry mass. Intra-cycle oscillations in dissolved (
• Choi, S., Amistadi, M. K., & Chorover, J. (2005). Clay mineral weathering and contaminant dynamics in a caustic aqueous system I. Wet chemistry and aging effects. Geochimica et Cosmochimica Acta, 69(18), 4425-4436.
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  Abstract: Caustic high level radioactive waste induces mineral weathering reactions that can influence the fate of radionuclides released in the vicinity of leaking storage tanks. The uptake and release of CsI and SrII were studied in batch reactors of 2:1 layer-type silicates-illite (Il), vermiculite (Vm) and montmorillonite (Mt)-under geochemical conditions characteristic of leaking tank waste at the Hanford Site in WA (0.05 M AlT, 2 M Na+, 1 M NO3-, pH ∼14, Cs and Sr present as co-contaminants). Time series (0 to 369 d) experiments were conducted at 298 K, with initial [Cs]0 and [Sr]0 concentrations from 10-5 to 10-3 mol kg-1. Clay mineral type affected the rates of (i) hydroxide promoted dissolution of Si, Al and Fe, (ii) precipitation of secondary solids and (iii) uptake of Cs and Sr. Initial Si release to solution followed the order Mt > Vm > Il. An abrupt decrease in soluble Si and/or Al after 33 d for Mt and Vm systems, and after 190 d for Il suspensions was concurrent with accumulation of secondary aluminosilicate precipitates. Strontium uptake exceeded that of Cs in both rate and extent, although sorbed Cs was generally more recalcitrant to subsequent desorption and dissolution. After 369 d reaction time, reacted Il, Vm and Mt solids retained up to 17, 47 and 14 mmol kg-1 (0.18, 0.24 and 0.02 μmol m-2) of Cs, and 0, 27 and 22 mmol kg-1 (0, 0.14 and 0.03 μmol m-2) Sr, respectively, which were not removed in subsequent Mg exchange or oxalic acid dissolution reactions. Solubility of Al and Si decreased with initial Cs and Sr concentration in Mt and Il, but not in Vm. High co-contaminant sorption to the Vm clay, therefore, appears to diminish the influence of those ions on mineral transformation rates. Copyright © 2005 Elsevier Ltd.
• Goyne, K. W., Chorover, J., Kubicki, J. D., Zimmerman, A. R., & Brantley, S. L. (2005). Sorption of the antibiotic ofloxacin to mesoporous and nonporous alumina and silica. Journal of Colloid and Interface Science, 283(1), 160-170.
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  PMID: 15694437;Abstract: Mesoporous and nonporous SiO2 and Al2O3 adsorbents were reacted with the fluoroquinolone carboxylic acid ofloxacin over a range of pH values (2-10) and initial concentrations (0.03-8 mM) to investigate the effects of adsorbent type and intraparticle mesopores on adsorption/desorption. Maximum ofloxacin adsorption to SiO2 surfaces occurs slightly below the pKa2 (pH 8.28) of the antibiotic and sorption diminishes rapidly at pH > pKa2. For Al2O 3, maximum sorption is observed at pH values slightly higher than the adsorbent's point of zero net charge (p.z.n.c.) and less than midway between the pKa values of ofloxacin. The effects of pH on adsorption and ATR-FTIR spectra suggest that the zwitterionic compound adsorbs to SiO 2 solids through the protonated N4 in the piperazinyl group and, possibly, a cation bridge; whereas the antibiotic sorbs to Al 2O3 solids through the ketone and carboxylate functional groups via a ligand exchange mechanism. Sorption edge and isotherm experiments show that ofloxacin exhibits a higher affinity for mesoporous SiO2 and nonporous Al2O3, relative to their counterparts. It is hypothesized that decreased ofloxacin sorption to mesoporous Al 2O3 occurs due to electrostatic repulsion within pore confines. In contrast, it appears that the environment within SiO2 mesopores promotes sorption by inducing formation of ofloxacin-Ca complexes, thus increasing electrostatic attraction to SiO2 surfaces. © 2004 Elsevier Inc. All rights reserved.
• Neaman, A., Chorover, J., & Brantley, S. L. (2005). Element mobility patterns record organic ligands in soils on early Earth. Geology, 33(2), 117-120.
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  Abstract: Considerable mobilization of Fe without mobilization of Al in Precambrian paleosols has been documented and attributed to either anoxic- or ligand-promoted dissolution. To elucidate these mechanisms, basalt was dissolved under oxic and anoxic conditions with and without citrate, and the mobility of several elements was analyzed. The extent of release of Fe and P was minor (in citrate-free conditions) or considerable (with citrate) regardless of oxygen pressure. Release of Al was minor in all cases, whereas release of Cu was minor (in anoxic conditions) or considerable (in oxic conditions). Release of Cu was enhanced by citrate. In comparison, in the weathered surface of two of the oldest-known basalt-derived paleosols-the Mount Roe (2.76 Ga) and the Hekpoort (2.25 Ga)-Fe and P were considerably depleted and Al retained, consistent with the presence of organic ligands. Cu, retained in the Mount Roe paleosol but considerably mobilized in the Hekpoort paleosol, documents formation under an anoxic atmosphere and an oxic atmosphere, respectively, as inferred by others on the basis of Fe mobility. The immobility of Al in both paleosols is consistent with formation under conditions in which the annual volume of rainwater was lower than the topsoil pore volume. Mobilization of P in such paleosols developed under low-rainfall conditions provides a new proxy for identification of ligands secreted by terrestrial organisms on early Earth. © 2005 Geological Society of America.
• Neaman, A., Chorover, J., & Brantley, S. L. (2005). Implications of the evolution of organic acid moieties for basalt weathering over geological time. American Journal of Science, 305(2), 147-185.
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  Abstract: Concentrations of organic acids in prebiotic soils were presumably low, given limitations in abiotic synthesis and the limited lifetimes of organic molecules before the ultraviolet shield developed on early Earth. Prokaryotes, the first land-colonizing organisms, commonly secrete aliphatic carboxylic acids, and, less extensively, secrete aromatic compounds as siderophores and antibiotics. In contrast, secretion of aromatic acids is considerable for fungi, lichens, and vascular plants. Aromatic acids are also produced by degradation of high-molecular-weight compounds from lignin and tannin, both abundant in vascular plants. The proportion of aromatic carboxylic acids in soil solutions therefore probably increased with the evolution of higher order organisms. As biomass of organisms increased over geological, time, concentrations of organic acids in soil solutions and, in turn, the extent of ligand-promoted dissolution of minerals probably increased. To elucidate the contribution of ligands during weathering on early Earth, Columbia River basalt was dissolved under oxic and anoxic conditions in the presence (0.001 or 0.01 M) and absence of several organic ligands in batch experiments at pH 6. Release of all elements including Si was enhanced considerably in the presence of organic ligands. Citrate (tridentate) and gallate (tetradentate) increased element release to the greatest extent among the aliphatic and aromatic ligands, respectively. The extent of element mobilization observed for the aliphatic ligands decreased in the order: citrate > oxalate ≈ malonate, and for the aromatic ligands: gallate > salicylate ≈ phthalate. The effects of the ligands generally followed trends in cation-ligand stability constants, but aromatic ligands were less effective in element mobilization than aliphatic ligands. One exception was gallate, an aromatic ligand, which significantly enhanced Cu release. Ligand-promoted mobilization of Cu may therefore have increased over geological time with the increase in the proportion of aromatic ligands. In the presence of organic ligands, Fe was mobilized from basa lt considerably more than Al even under oxic conditions. Complexation of Fe with organic ligands may have mobilized Fe in Precambrian paleosols where little Al mobility is observed. Extent of P and Y release was minor in ligand-free experiments and considerable with ligands regardless of PO2. Release of Cu was considerable under oxic conditions, especially with ligands, and minor under anoxic conditions. Mobility patterns of P and Y could thus possibly serve as "organomarkers" (indicative of prevalence of organic ligands in soil solutions) and mobility patterns of Cu could possibly serve as "oxymarkers" (indicative of the presence of molecular oxygen), respectively, in ancient soils.
• Parikh, S. J., & Chorover, J. (2005). FTIR spectroscopic study of biogenic Mn-oxide formation by Pseudomonas putida GB-1. Geomicrobiology Journal, 22(5), 207-218.
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  Abstract: Biomineralization in heterogeneous aqueous systems results from a complex association between pre-existing surfaces, bacterial cells, extracellular biomacromolecules, and neoformed precipitates. Fourier transform infrared (FTIR) spectroscopy was used in several complementary sample introduction modes (attenuated total reflectance [ATR], diffuse reflectance [DRIFT], and transmission) to investigate the processes of cell adhesion, biofilm growth, and biological Mn-oxidation by Pseudomonas putida strain GB-1. Distinct differences in the adhesive properties of GB-1 were observed upon Mn oxidation. No adhesion to the ZnSe crystal surface was observed for planktonic GB-1 cells coated with biogenic MnOx, whereas cell adhesion was extensive and a GB-1 biofilm was readily grown on ZnSe, CdTe, and Ge crystals prior to Mn-oxidation. IR peak intensity ratios reveal changes in biomolecular (carbohydrate, phosphate, and protein) composition during biologically catalyzed Mn-oxidation. In situ monitoring via ATR-FTIR of an active GB-1 biofilm and DRIFT data revealed an increase in extracellular protein (amide I and II) during Mn(II) oxidation, whereas transmission mode measurements suggest an overall increase in carbohydrate and phosphate moieties. The FTIR spectrum of biogenic Mn oxide comprises Mn-O stretching vibrations characteristic of various known Mn oxides (e.g., "acid" birnessite, romanechite, todorokite), but it is not identical to known synthetic solids, possibly because of solid-phase incorporation of biomolecular constituents. The results suggest that, when biogenic MnOx accumulates on the surfaces of planktonic cells, adhesion of the bacteria to other negatively charged surfaces is hindered via blocking of surficial proteins. Copyright © Taylor & Francis Inc.
• Reich, P. B., Oleksyn, J., Modrzynski, J., Mrozinski, P., Hobbie, S. E., Eissenstat, D. M., Chorover, J., Chadwick, O. A., Hale, C. M., & Tjoelker, M. G. (2005). Linking litter calcium, earthworms and soil properties: A common garden test with 14 tree species. Ecology Letters, 8(8), 811-818.
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  Abstract: Tree species can influence biogeochemistry through variation in the quantity and chemistry of their litter, and associated impacts on the soil heterotrophic community. However, the role that different plant traits play in these processes is not well understood, nor is it clear whether species effects on soils largely reflect a gymnosperm vs. angiosperm contrast. Using a replicated, long-term monoculture plot experiment, we examined variation in soils among 14 gymnosperm and angiosperm tree species 30 years after plot establishment, and assessed the role of litter chemistry vis-à-vis such variation. Differences in litter calcium concentrations among tree species resulted in profound changes in soil acidity and fertility that were similar within and among tree groups. Tree species rich in calcium were associated with increased native earthworm abundance and diversity, as well as increased soil pH, exchangeable calcium, per cent base saturation and forest floor turnover rate. ©2005 Blackwell Publishing Ltd/CNRS.
• Anderson, S. P., Blum, J., Brantley, S. L., Chadwick, O., Chorover, J., Derry, L. A., Drever, J. I., Hering, J. G., Kirchner, J. W., Kump, L. R., Richter, D., & White, A. F. (2004). Proposed initiative would study earth's weathering engine. Eos, 85(28), 265+269.
• Chorover, J., Amistadi, M. K., & Chadwick, O. A. (2004). Surface charge evolution of mineral-organic complexes during pedogenesis in Hawaiian basalt. Geochimica et Cosmochimica Acta, 68(23), 4859-4876.
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  Abstract: Changes in surface charge of soil particles that accompany mineral transformations during soil formation were measured for a humid tropical chronosequence in Hawaiian basalt ranging in lava flow age from 0.3 to 4100 kiloyears (ky). Parent mineralogy is dominated by glass, olivine, pyroxene, and feldspar, whereas poorly crystalline (PC) weathering products (allophane, microcrystalline gibbsite, ferrihydrite) accumulate in early to intermediate weathering stages (through 400 ky), and crystalline secondary minerals (kaolinite, gibbsite, goethite) are dominant in the oldest (1400 and 4100 ky) soils. Detailed characterization of the solid phase was accomplished with chemical extractions, X-ray diffraction analysis, and molecular spectroscopy (FTIR and 13C MAS NMR). Simultaneous proton titration and background ion adsorption measurements were made on LiCl saturated soils over a range in pH (2-9) and ionic strength (0.001 and 0.01 M LiCl). Dependence of variable surface charge on solution composition reflects the changing nature of mineral-organic interactions over the course of pedogenesis. Points of zero net proton charge (PZNPC) ranged from 3.4 to 6.2 and 2.0 to 5.8 at 0.001 and 0.01 M ionic strength (I), respectively. Intermediate-aged soils containing the highest mass concentration of humified soil organic matter (SOM) and its complexes with PC minerals gave rise to the steepest charging curves (largest pH dependence) and highest PZNPC values. Surface charge properties of these soils most closely reflected their weakly acidic Al and Fe hydroxide constituents, which is consistent with metal hydroxide saturation of organic functional groups, rather than organic coating of mineral surfaces. Charging curves were less steep and PZNPC values were lower for the older soils, consistent with SOM coating of more crystalline goethite, kaolinite, and gibbsite surfaces in a soil system less impacted by labile Al and Fe. Copyright © 2004 Elsevier Ltd.
• Goyne, K. W., Chorover, J., Zimmerman, A. R., Komarneni, S., & Brantley, S. L. (2004). Influence of mesoporosity on the sorption of 2,4-dichlorophenoxyacetic acid onto alumina and silica. Journal of Colloid and Interface Science, 272(1), 10-20.
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  PMID: 14985017;Abstract: Two SiO2 and three Al2O3 adsorbents with varying degrees of mesoporosity (pore diameter 2-50 nm) were reacted with 2,4-dichlorophenoxyacetic acid (2,4-D) at pH 6 to investigate the effects of intraparticle mesopores on adsorption/desorption. Anionic 2,4-D did not adsorb onto either SiO2 solid, presumably because of electrostatic repulsion, but it did adsorb onto positively charged Al2O 3 adsorbents, resulting in concave isotherms. The Al 2O3 adsorbent of highest mesoporosity consistently adsorbed more 2,4-D per unit surface area than did the nonporous and less mesoporous Al2O3 adsorbents over a range of initial 2,4-D solution concentrations (0.025-2.5 mM) and reaction times (30 min-55 d). Differences in adsorption efficiency were observed despite equivalent surface site densities on the three Al2O3 adsorbents. Hysteresis between the adsorption/desorption isotherms was not observed, indicating that adsorption is reversible. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy studies confirm that 2,4-D adsorption does not occur via ligand exchange, but rather via electrostatic interaction. The results indicate that adsorbent intraparticle mesopores can result in consistently greater 2,4-D adsorption, but the amount adsorbed is dependent upon surface charge and the presence of adsorbent mesoporosity. The data also suggest that when mineral pores are significantly larger than the adsorbate, they do not contribute to diffusion-limited adsorption/desorption hysteresis. Adsorbent transformations through time are discussed. © 2004 Elsevier Inc. All rights reserved.
• Guo, M., & Chorover, J. (2004). Solute release from weathering of spent mushroom substrate under controlled conditions. Compost Science and Utilization, 12(3), 225-234.
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  Abstract: Weathering of piled material in the field is a popular method to treat spent mushroom substrate (SMS) before reuse. During the weathering process, rainfall and snowmelt pass through SMS piles and a large amount of solutes is released in the leachate. To investigate solute release patterns, the field weathering process was simulated under controlled conditions in the laboratory. Fresh SMS was packed in an acrylic column (20 cm i.d.) to 150 cm height and leached intermittently with a cumulative total of 230 cm of deionized water over 180 days. Leachate was collected and analyzed for dissolved organic carbon (DOC), dissolved organic nitrogen (DON), electrical conductivity (EC), and inorganic salts. Solute release patterns were described using first order models, and total released solutes were calculated. The SMS leachate had DOC, DON and EC values ranging from 450 to 15,500 mg L-1 50 to 1,700 mg L-1, and 3 to 50 dS m-1, respectively. The major inorganic cations were K+, Na+, Ca 2+, and Mg2+ and NH+, and anions were CT and SO42-. Release of DOC, DON, and bivalent cations Ca2+ and Mg2+ were described by a first order Exponential Rise to Maximum model, while releases of monovalent ions Cl-, K+, Na+ and NH 4+ were described as a first order Sigmoidal Logistic process, and SO42- release was best modeled by a Sigmoidal Chapman equation. Following six months and 230 cm applied water, 3.1 kg of DOC, 0.58 kg of dissolved N, and 8.6 kg of inorganic salts were leached per cubic meter of bulk SMS (220 kg oven dry mass). Weathering of SMS involves a significant removal of nutrients from the composted material, which can contribute to pollution of soil and groundwater.
• Omoike, A., & Chorover, J. (2004). Spectroscopic study of extracellular polymeric substances from Bacillus subtilis: Aqueous chemistry and adsorption effects. Biomacromolecules, 5(4), 1219-1230.
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  PMID: 15244434;Abstract: Reactions at ionizable functional groups in extracellular polymeric substances (EPS) from Bacillus subtilis are found to affect aqueous phase conformation and adsorption to mineral surfaces. Characterization by HPSEC, XPS, and FTIR indicates a wide range in apparent molecular mass (0.57-128 kDa), with functional group composition depending on cell growth phase (exponential vs stationary) and location in suspension (free vs cell-bound). ATR-FTIR spectroscopy shows complexation and dissociation of protons on acidic functional groups that result in α-helical protein conformation at pH < 2.6 and random coil (unordered) conformation at higher pH (>6). EPS exhibit higher affinity for adsorption to α-FeOOH than amorphous SiO2 because of surface charge effects. Increased amide II band intensity and an amide I band shift to higher frequency indicate changes in protein structure upon adsorption. Goethite-EPS spectra show emergent vibrations consistent with P-O-Fe bonding, which suggests a role of phosphodiester groups in the adsorption reaction. © 2004 American Chemical Society.
• Omoike, A., Chorover, J., Kwon, K. D., & Kubicki, J. D. (2004). Adhesion of bacterial exopolymers to α-FeOOH: Inner-sphere complexation of phosphodiester groups. Langmuir, 20(25), 11108-11114.
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  PMID: 15568864;Abstract: Extracellular polymeric substances (EPS) constitute a heterogeneous mixture of polyelectrolytes that mediate biomineralization and bacterial adhesion and stabilize biofilm matrixes in natural and artificial environments. Although nucleic acids are exuded extracellularly and are purported to be required for biofilm formation, direct evidence of the active mechanism is lacking. EPS were extracted from both Bacillus subtilis (a gram-positive bacterium) and Pseudomonas aeruginosa (a gram-negative bacterium) and their interaction with the goethite (α-FeOOH) surface was studied using attenuated total internal reflection infrared spectroscopy. Correspondence between spectral data and quantum chemical calculations demonstrate that phosphodiester groups of nucleic acids mediate the binding of EPS to mineral surfaces. Our data indicate that these groups emerge from the EPS mixture to form monodentate complexes with Fe centers on the goethite (α-FeOOH) surface, providing an energetically stable bond for further EPS or cell adhesion.
• Parikh, S. J., Chorover, J., & Burgos, W. D. (2004). Interaction of phenanthrene and its primary metabolite (1-hydroxy-2- naphthoic acid) with estuarine sediments and humic fractions. Journal of Contaminant Hydrology, 72(1-4), 1-22.
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  PMID: 15240164;Abstract: Experiments were conducted to compare the sorption and desorption of phenanthrene and its primary degradation product, 1-hydroxy-2-naphthoic acid (HNA), in estuarine sediment, humic acid (HA) and humin. Ionic composition, ionic strength (0.4 M) and pH (7.6) were employed to mimic native estuarine pore water at the sediment-water interface. Sorption to whole sediment and organic matter (OM) fractions was significantly lower for HNA than for phenanthrene. Whereas HNA did not sorb to HA, uptake to sediment and humin was observed, suggesting that HNA does not bind directly to OM. Phenanthrene uptake was characterized by hysteretic behavior and exhibited slow desorption. In contrast, HNA initially was more readily desorbed from sediment and humic fractions, but a significant fraction was not recovered in repeated desorption runs. The lower sorption of HNA reflects its greater polarity and water solubility, but the consistent retention of a non-desorbing fraction suggests strong binding and/or chemical transformation reactions may be important. It was postulated that abiotic transformation of HNA may occur in estuarine sediments, in part due to the presence of redox active minerals (Fe(III) and Mn(IV) oxides). The presence of Fe and Mn solids in the estuarine sediment was verified by sequential extraction and studies were then conducted to investigate the transformation of HNA in the presence of synthetic goethite (α-FeOOH) and birnessite (δ-MnO2) as model solids. Reaction with birnessite led to transformation of all HNA in solution within 24 h and resulted in the formation of partial oxidation products (POPs). Following reaction with goethite, HNA was present in solution and POPs were observed in the weakly bound fraction. This study indicates that degradation products of polycyclic aromatic hydrocarbons (PAHs) may have distinctly different sorption affinities and reactivities toward environmental surfaces than their parent compounds. © 2003 Elsevier B.V. All rights reserved.
• Zimmerman, A. R., Chorover, J., Goyne, K. W., & Brantley, S. L. (2004). Protection of mesopore-adsorbed organic matter from enzymatic degradation. Environmental Science and Technology, 38(17), 4542-4548.
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  PMID: 15461161;Abstract: Synthetic mesoporous alumina and silica minerals with uniform pore geometries, and their nonporous analogues, were used to test the role of mineral mesopores (2-50 nm diameter) in protecting organic matter from enzymatic degradation in soils and sediments. Dihydroxyphenylalanine (L-DOPA), a model humic compound, was irreversibly sorbed to both mineral types. The surface area-normalized adsorption capacity was greater for the mesoporous minerals relative to their nonporous analogues. The degradation kinetics of free and mineral-sorbed L-DOPA by the enzyme laccase was monitored in a closed cell via oxygen electrode. Relative to freely dissolved L-DOPA, nonporous alumina-sorbed substrate was degraded, on average, 90% more slowly and to a lesser extent (93%), likely due to laccase adsorption to alumina. In contrast, relative to free L-DOPA, degradation of nonporous silica-sorbed L-DOPA was enhanced by 20% on average. In the case of mesoporous alumina and silica-sorbed L-DOPA, the enzyme activity was 3-40 times lower than that observed for externally sorbed substrate (i.e., L-DOPA sorbed to nonporous minerals). These results provide strong evidence to support the viability of the mesopore protection mechanism for sequestration and preservation of sedimentary organic matter and organic contaminants. Nanopore adsorption/desorption phenomena may aid in explaining the slow degradation of organic contaminants in certain soils and sediments and may have implications for environmental remediation and biotechnological applications.
• Zimmerman, A. R., Goyne, K. W., Chorover, J., Komarneni, S., & Brantley, S. L. (2004). Mineral mesopore effects on nitrogenous organic matter adsorption. Organic Geochemistry, 35(3), 355-375.
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  Abstract: The "mesopore protection hypothesis" [Chem. Geol. 114 (1994) 347; Geochim. Cosmochim. Acta 58 (1994) 1271] proposes that organic matter (OM) may be protected from enzymatic degradation by sequestration within mineral mesopores (2-50 nm diameter). This hypothesis is a leading, though controversial, theory in explaining both the preservation of some extremely labile OM compounds and observed correlations between OM content and mineral surface area in soils and sediments. To test this idea, we carried out batch experiments in aqueous suspensions to examine the adsorption/desorption of amino acid monomers and polymers onto fabricated mesoporous and nonporous alumina and silica. Each mineral pair was of similar surface chemistry and differed only in the presence or absence of intraparticle mesoporosity. All amino acid monomers and polymers smaller than about one-half the pore diameter exhibited significantly greater surface area-normalized adsorption to mesoporous alumina (8.2 nm mean pore diameter) and silica (3.4 nm mean pore diameter) compared to nonporous mineral analogues. Proteins larger than the mesopores exhibited greater adsorption to the nonporous phases indicating their exclusion from internal surfaces of mesoporous minerals. Greater desorption hysteresis for mesopore-sorbed OM indicates that desorption from pores was inhibited. The adsorption/desorption data, as well as Langmuir-Freundlich modeling and adsorption affinity distributions, suggest that capillary condensation, a 'pore-filling' mechanism, may explain the experimental observations. These results provide a potential mechanism for the selective sequestration and preservation of sedimentary OM as well as organic contaminants. © 2003 Elsevier Ltd. All rights reserved.
• Chorover, J., Choi, S., Amistadi, M. K., Karthikeyan, K. G., Crosson, G., & Mueller, K. T. (2003). Linking cesium and strontium uptake to kaolinite weathering in simulated tank waste leachate. Environmental Science and Technology, 37(10), 2200-2208.
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  PMID: 12785526;Abstract: Weathering behavior of kaolinite was studied in batch systems under geochemical conditions characteristic of tank waste released to the vadose zone at the Hanford Site, WA (0.05 M AIT, 2 M Na+, 1 M NO3-, pH ∼14, Cs+ and Sr2+ present as co-contaminants). Time series experiments were conducted from 0 to 369 d, with initial Cs+ and Sr2+ concentrations ranging from 10-5 to 10-3 M. Dissolution of kaolinite increased soluble Si and Al to maximum levels at 7 d (Cs and Sr concentrations of 10-5 and 10-4 M) or 33 d (Cs and Sr concentrations of 10-3 M). Subsequent precipitation of Si and Al was coupled to the formation of oxalate-extractable solids that incorporated Cs and Sr. Strontium sorption was nearly complete within 24 h for initial Sr concentrations (Sr0) ≤ 10-4 whereas Cs uptake increased over the full year of the experiment for all initial Cs concentrations. Spectroscopic analyses revealed neoformed solids including the zeolite Na-Al silicate (Alchabazite), and feldspathoids sodium aluminum nitrate silicate (NO3-sodalite), and sodium aluminum nitrate silicate hydrate (NO3-cancrinite), which can incorporate Cs. Singlepulse 27Al solid-state nuclear magnetic resonance (NMR) spectroscopy yielded first-order rate constants (k)for mineral transformation that decreased from 3.5 × 10-3 to 2 × 10-3 d-1 as Cs and Sr concentrations were increased from 10-5 to 10-3 M. Discrete strontium silicate solids were also observed. The incongruent dissolution of kaolinite promoted the sequestration of contaminants into increasingly recalcitrant solid phases over the 1-yr time period.
• Davidson, E. A., Chorover, J., & Dail, D. B. (2003). A mechanism of abiotic immobilization of nitrate in forest ecosystems: The ferrous wheel hypothesis. Global Change Biology, 9(2), 228-236.
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  Abstract: Forest soils, rather than woody biomass, are the dominant long-term sink for N in forest fertilization studies and, by inference, for N from atmospheric deposition. Recent evidence of significant abiotic immobilization of inorganic-N in forest humus layers challenges a previously widely held view that microbial processes are the dominant pathways for N immobilization in soil. Understanding the plant, microbial, and abiotic mechanisms of N immobilization in forest soils has important implications for understanding current and future carbon budgets. Abiotic immobilization of nitrate is particularly perplexing because the thermodynamics of nitrate reduction in soils are not generally favorable under oxic conditions. Here we present preliminary evidence for a testable hypothesis that explains abiotic immobilization of nitrate in forest soils. Because iron (and perhaps manganese) plays a key role as a catalyst, with Fe(II) reducing nitrate and reduced forms of carbon then regenerating Fe(II), we call this 'the ferrous wheel hypothesis'. After nitrate is reduced to nitrite, we hypothesize that nitrite reacts with dissolved organic matter through nitration and nitrosation of aromatic ring structures, thus producing dissolved organic nitrogen (DON). In addition to ignorance about mechanisms of DON production, little is known about DON dynamics in soil and its fate within ecosystems. Evidence from leaching and watershed studies suggests that DON production and consumption may be largely uncoupled from seasonal biological processes, although biological processes ultimately produce the DOC and reducing power that affect DON formation and the entire N cycle. The ferrous wheel hypothesis includes both biological and abiological processes, but the reducing power of plant-derived organic matter may build up over seasons and years while the abiotic reduction of nitrate and reaction of organic matter with nitrite may occur in a matter of seconds after nitrate enters the soil solution.
• Guo, M., & Chorover, J. (2003). Transport and fractionation of dissolved organic matter in soil columns. Soil Science, 168(2), 108-118.
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  Abstract: Dissolved organic matter (DOM) is a heterogeneous mixture of organic compounds that plays an important role in the movement of DOM-associated pollutants. In this study, transport and fractionation of DOM in soils was investigated in flow-through soil columns. Dissolved organic matter derived from spent mushroom substrate weathering was pumped through packed columns (2.5 cm × 10 cm) comprising a coarseloamy subsoil (mixed, semiactive, mesic Typic Hapludult), and effluents were monitored for changes in the composition of DOM. Effluent DOM was characterized for UV absorbance, molecular weight, acidity, and hydrophilicity. Transport through the columns resulted in preferential retention of specific DOM constituents as indicated by comparison with a Br- tracer. During the transport process, effluent DOM exhibited decreasing values of E2/E3 (from 10.3 to 6.2), acidity (from 20.8 to 13.1 mmolc g-1 C), and hydrophilicity (39.0 to 28.4%), and increasing values of molar absorptivity (from 164 to 310 L mol-1C cm-1) and number and weight-averaged molecular weight (from 1770 to 3150 and 2450 to 4180 Da, respectively). These results indicate that DOM fractions with higher molecular weight, higher molar absorptivity, lower E2/E3 ratio, lower acidity, and lower hydrophilicity were adsorbed preferentially by soil minerals, whereas the inverse fractions were transported preferentially. The adsorbed DOM could not be completely desorbed by DOM-free background solution, indicating a strongly bound fraction. Sorptive fractionation of DOM during transport likely affects the transport behavior of DOM-complexed constituents.
• Bostick, B. C., Vairavamurthy, M. A., Karthikeyan, K. G., & Chorover, J. (2002). Cesium adsorption on clay minerals: An EXAFS spectroscopic investigation. Environmental Science and Technology, 36(12), 2670-2676.
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  PMID: 12099463;Abstract: Cesium adsorption on the clay minerals vermiculite and montmorillonite is described as a function of surface coverage using extended X-ray adsorption fine structure spectroscopy (EXAFS). Cesium (Cs) possessed a variable coordination environment consisting of Cs-0 distances between 3.2 and 4.3, Å; however, disorder typical of the Cs coordination environments prevented the resolution of all oxygen shells. On the basis of the influence of Cs loading and exchangeability on this structural arrangement, we could recognize both inner-sphere and outer-sphere adsorption complexes. The shorter Cs-0 bond distance belongs to outer-sphere complexes typical of hydrated ions. In inner-sphere complexes, partially or fully dehydrated Cs coordinates directly to siloxane groups of the clay minerals forming longer Cs-0 bonds. The inner-sphere adsorption complexes may have occurred within the interlayer or at frayed edge sites and were less extractable than the outersphere complexed Cs. Both coordination number ratios and linear combination fitting of EXAFS spectra were useful in estimating the fractions of inner-sphere and outersphere adsorption complexes. Our results show that X-ray absorption spectroscopy (XAS), and particularly EXAFS, is a valuable technique for exploring the type of Cs binding in environmental samples.
• Burgos, W. D., Pisutpaisal, N., Mazzarese, M. C., & Chorover, J. (2002). Adsorption of quinoline to kaolinite and montmorillonite. Environmental Engineering Science, 19(2), 59-68.
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  Abstract: Adsorption of quinoline (pKa = 4.92) and background electrolyte (CaCl2) onto specimen kaolinite and montmorillonite were measured as a function of pH (3-7.5) and ionic strength (1-10 mM), and as a function of quinoline concentration (0.2-1.55 mM) at fixed pH values of maximum adsorption. Maximum sorption of quinoline occurred at pH 3.5-4.0 for kaolinite, and pH 3.0-5.0 for montmorillonite. At their respective pH values of maximum adsorption, the sorption capacity for quinoline was 100 times greater with montmorillonite than kaolinite on a mass basis. Selectivity coefficients, which were calculated from pH edge data, indicated selectivity for cationic quinoline (QH+) over Ca2+ was greater with montmorillonite (Kexc = 27 at pH 4) compared to kaolinite (Kexc = 1.6 at pH 4), and Kexc was not affected by ionic strength for either clay. The results indicate the important role of charged siloxane sites in the adsorption of this N-heterocyclic contaminant.
• Goyne, K. W., Zimmerman, A. R., Newalkar, B. L., Komarneni, S., Brantley, S. L., & Chorover, J. (2002). Surface charge of variable porosity Al₂O₃(s) and SiO₂(s) adsorbents. Journal of Porous Materials, 9(4), 243-256.
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  Abstract: The surface charge properties of two SiO2 and three Al2O3 mineral adsorbents with varying degrees of framework porosity were investigated using discontinuous titration and ion adsorption methodologies. Points of zero net change (p.z.n.c.) for porous SiO2 were
• Karthikeyan, K. G., & Chorover, J. (2002). Humic acid complexation of basic and neutral polycyclic aromatic compounds. Chemosphere, 48(9), 955-964.
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  PMID: 12222791;Abstract: Complexation by humic acid (HA) of basic (quinoline) and neutral (naphthalene) polycyclic aromatic compounds (PACs) was compared using fluorescence spectroscopy and equilibrium dialysis (ED). These compounds sorb to HA via cation exchange and hydrophobic interactions, respectively. Ionization of quinoline strongly affects its sorption to HA; maximum sorption is observed at pH close to log Kb (4.92), and competition with H+ and electrolyte cation (Li+) is evident. Spectroscopic experiments indicate that quinolinium (QH+) cation fluorescence is quenched via a static mechanism (i.e., a dark complex is formed) when the protonated form is adsorbed via ion exchange to HA. The extent of sorption, calculated from fluorescence data using the Stern-Volmer equation, was compared to independent ED measurements. Although both methods indicated the same trends with solution chemistry, fluorescence quenching data suggested more extensive complexation than that measured using ED. In contrast to ionizable PACs, studied here and previously, interaction of naphthalene with HA is unaffected by changes in solution conditions (pH, ionic strength). © 2002 Elsevier Science Ltd. All rights reserved.
• Chadwick, O. A., & Chorover, J. (2001). The chemistry of pedogenic thresholds. Geoderma, 100(3-4), 321-353.
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  Abstract: Pedogenesis can be slow or fast depending on the internal chemical response to environmental forcing factors. When a shift in the external environment does not produce any pedogenic change even though one is expected, the soil is said to be in a state of pedogenic inertia. In contrast, soil properties sometimes change suddenly and irreversibly in a threshold response to external stimuli or internal change in soil processes. Significant progress has been made in understanding the thermodynamics and kinetics of soil-property change. Even in the open soil system, the direction of change can be determined from measures of disequilibrium. Favorable reactions may proceed in parallel, but the most prevalent and rapid ones have the greatest impact on product formation. Simultaneous acid-base, ion exchange, redox and mineral-transformation reactions interact to determine the direction and rate of change. The nature of the governing reactions is such that soils are well buffered to pH change in the alkaline and strongly acid regions but far less so in the neutral to slightly acid zones. Organic matter inputs may drive oxidation-reduction processes through a stepwise consumption of electron acceptors (thereby producing thresholds) but disequilibrium among redox couples and regeneration of redox buffer capacity may attenuate this response. Synthesis of secondary minerals, ranging from carbonates and smectites to kaolinite and oxides, forms a basis for many of the reported cases of pedogenic inertia and thresholds. Mineralogical change tends to occur in a serial, irreversible fashion that, under favorable environmental conditions, can lead to large accumulations of specific minerals whose crystallinity evolves over time. These accumulations and associated "ripening" processes can channel soil processes along existing pathways or they can force thresholds by causing changes in water flux and kinetic pathways. © 2001 Elsevier Science B.V.
• Chorover, J., & Amistadi, M. K. (2001). Reaction of forest floor organic matter at goethite, birnessite and smectite surfaces. Geochimica et Cosmochimica Acta, 65(1), 95-109.
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  Abstract: Experiments were conducted to compare the affinity and reactivity of three different minerals for natural organic matter (NOM) in forest floor leachate (FFL) from hardwood and pine forests. The FFLs were acidic (pH 4) with ionic strengths of 1.4 mM (hardwood) and 1.1 mM (pine), and they contained larger organic molecules (weight average molecular weights [Mw] = 5-6 kDa) than has been reported recently for surface waters using similar methods. A synthetic diluent solution was prepared to match the inorganic chemistry of the FFL and to provide a range of initial dissolved organic carbon (DOC) concentrations (0-140 g C m3) for reaction with goethite (α-FeOOH), birnessite (δ-MnO2) and smectite (montmorillonite, SWy-2) in suspension, and in corresponding blanks. A variety of macroscopic and spectroscopic methods were employed to show that reaction with the three minerals resulted in distinctly different NOM adsorption, fractionation and transformation patterns. Goethite exhibited a steep initial slope in the adsorption isotherm and a maximum retention of 10.5 g C kg1. The isotherm for montmorillonite was more linear, but equal amounts of C were adsorbed to goethite and montmorillonite (per unit sorbent mass) at maximum DOC. Whereas preferential uptake of high Mw, aromatic constituents via ligand exchange was observed for goethite, compounds of lower than average Mw were retained on montmorillonite and no preference for aromatic moieties was observed. Birnessite, which has an isoelectric point of pH < 2, retained low amounts of organic C (
• Dail, D. B., Davidson, E. A., & Chorover, J. (2001). Rapid abiotic transformation of nitrate in an acid forest soil. Biogeochemistry, 54(2), 131-146.
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  Abstract: Nitrate immobilization into organic matter is thought to require catalysis by the enzymes of soil microorganisms. However, recent studies suggest that nitrate added to soil is immobilized rapidly and this process may include abiotic pathways. We amended living and sterilized soil with 15N-labeled nitrate and nitrite to investigate biotic and abiotic immobilization. We report rapid transformation of nitrate in incubations of the O layer of forest soils that have been sterilized to prevent microbial activity and to denature microbial enzymes. Approximately 30, 40, and 60% of the 15N-labeled nitrate added to live, irradiated, or autoclaved organic horizon soil disappeared from the extractable inorganic-N pool in less than 15 minutes. About 5% or less of the nitrate was recovered as insoluble organic N in live and sterilized soil, and the remainder was determined to be soluble organic N. Added 15N-nitrite, however, was either lost to gaseous N or incorporated into an insoluble organic N form in both live and sterile organic soils. Hence, the fate and pathway of apparent abiotic nitrate immobilization differs from the better-known mechanisms of nitrite reactions with soil organic matter. Nitrate and nitrite added to live A-horizon soil was largely recovered in the form added, suggesting that rapid conversion of nitrate to soluble organic-N may be limited to C-rich organic horizons. The processes by which this temperate forest soil transforms added nitrate to soluble organic-N cannot be explained by established mechanisms, but appears to be due to abiotic processes in the organic horizon.
• Guo, M., Chorover, J., & Fox, R. H. (2001). Effects of spent mushroom substrate weathering on the chemistry of underlying soils. Journal of Environmental Quality, 30(6), 2127-2134.
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  PMID: 11790023;Abstract: Passive weathering of heaped material in the field is a popular method for treating spent mushroom substrate (SMS) before its reuse. During the weathering process, leachate containing high concentrations of dissolved organic matter and inorganic salts is released into the underlying soils, but effects on soil and ground water quality remain uncertain. We conducted a field study to measure the effects of SMS weathering on chemical and morphological properties of underlying soils. Two SMS piles, 20 m long, 6 m wide, and either 90 or 150 cm high, were placed in a fallow agricultural field dominated by grasses and weathered for 24 mo. Soil samples were taken from each genetic horizon under the SMS piles following their removal and analyzed for pH, total organic carbon (TOC), electrical conductivity (EC), water-soluble organic carbon (WSOC), water-soluble inorganic cations and anions, and exchangeable inorganic cations. Compared with an unaffected control, SMS weathering did not raise soil TOC, but did alter soil pH, and significantly increased EC, WSOC, and water-soluble and exchangeable inorganic ions. At 200 cm below the soil surface, the EC, WSOC, and water-soluble Cl-, NO3-, Ca2+, Mg2+, Na+, and K+ under SMS piles were 4 to 20 times higher than in unaffected soils. Water-soluble NO3- was minimal in the surface soil but peaked in the C horizon (120-180 cm) under the 90-cm SMS pile, indicating that these soils may have little capacity for retaining NO3-. Concentration profiles of the different solutes reflect their relative mobilities in the soil environment and indicate the potential for effects on subsurface water supplies.
• Guo, M., Chorover, J., Rosario, R., & Fox, R. H. (2001). Leachate chemistry of field-weathered spent mushroom substrate. Journal of Environmental Quality, 30(5), 1699-1709.
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  PMID: 11577879;Abstract: Passive leaching by rainfall and snowmelt is a popular method to treat piles of spent mushroom substrate (SMS) before its reuse. During this field weathering process, leachate percolates into the underlying soils. A field study was conducted to examine the chemistry of SMS leachate and effects of infiltration. Two SMS piles were deposited (90 and 150 cm in height) over a Typic Hapludult and weathered for 24 mo. Leachate was collected biweekly using passive capillary samplers. The SMS leachate contained high concentrations of dissolved organic carbon (DOC; 0.8-11.0 g L-1), dissolved organic nitrogen (DON; 0.1-2 g L-1), and inorganic salts. The pH, electrical conductivity, and acid neutralizing capacity were 6.6 to 9.0, 21 to 66 ds m-1, and 10 to 75 mmolc L-1, respectively. Inorganic chemistry of the leachate was dominated by K+, Cl-, and SO42-. Leachate DOC was predominantly low molecular weight (
• Burgos, W. D., Pisutpaisal, N., Tuntoolavest, M., Chorover, J., & Unz, R. F. (2000). Short communication: Biodegradation of 1-naphthol in the presence of humic acid. Environmental Engineering Science, 17(6), 343-351.
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  Abstract: Biodegradation of 1-naphthol by a pure culture was measured in the presence (65 mg C L-1) and absence of a forest soil humic acid (HA). Experiments were performed under nongrowth conditions and controlled ionic strength (I equivalent to 10 mM LiCl) at pH 8.0. 1-Naphthol was allowed to react with HA under aerobic conditions in the dark for 7 days to promote sorption prior to bacterial inoculation. During this abiotic sorption period, 3.7-12% of 1-naphthol was transformed into oxidative products (naphthoquinones). At low initial 1-naphthol concentrations (9.0 mg L-1) with or without HA. Both abiotic and biotic 1-naphthol transformation pathways accumulated similar products, and these products were more recalcitrant than 1-naphthol. The sorption of 1-naphthol abiotic transformation products and bacterial metabolites to HA (not 1-naphthol) reduced 1-naphthol mineralization.
• Chefetz, B., D., J., Chen, Y., Romaine, C. P., Chorover, J., Rosario, R., Mingxin, G., & Hatcher, P. G. (2000). Organic matter transformations during the weathering process of spent mushroom substrate. Journal of Environmental Quality, 29(2), 592-602.
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  Abstract: The weathering process of spent mushroom substrate (SMS) was studied to better understand the chemical properties and transformations of organic matter (OM) during the process. The SMS was piled (20 m by 6 m row of 1.5 m height) in an open field and weathered during 15 mo. Chemical properties of the OM collected from the top and bottom parts of the weathering pile were studied using 13C-nuclear magnetic resonance (NMR), tetramethylammonium hydroxide (TMAH) thermochemolysis-gas chromatograph/mass spectrometry (GC/MS), and pyrolysis-gas chromatograph/mass spectrometry (PyGC/MS). The 13C-NMR data suggested that weathered SMS from the top part of the pile degraded rapidly: the relative level of polysaccharides decreased by 33% while the level of aromatic C increased by 21% during the process. The TMAH thermochemolysis chromatogram exhibited peaks of methylated derivatives of phenyl, guaiacyl and syringyl structures as well as some fatty acid methyl esters. Lignin-derived products from TMAH thermochemolysis indicate that preferential degradation of syringyl units and oxidation of Cα-Cβ bonds occurred in the SMS from the top part of the pile. In contrast, no major changes in lignin-derived structures were observed in the weathered SMS from the bottom part of the pile. The 13C-NMR, Py-GC/MS and TMAH thermochemolysis-GC/MS analyses indicated that the SMS decomposed rapidly at the top part of the weathering pile, whereas decomposition at the bottom of the pile was significantly slower, probably due to lack of oxygen. These analyses were shown to be useful techniques for the characterization of degradation processes in SMS. Therefore, their application to studies on OM transformation and humification processes is highly recommended.
• Goyne, K. W., Day, R. L., & Chorover, J. (2000). Artifacts caused by collection of soil solution with passive capillary samplers. Soil Science Society of America Journal, 64(4), 1330-1336.
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  Abstract: Soil solution was collected with passive capillary samplers (PCAPS) and zero-tension samplers (ZTS) from A horizons of forested soils. The volume and chemistry of collected solutions were measured weekly during discrete seasonal collection periods. Acid-washed PCAPS increased alkalinity (3-fold), pH (1-3 units), and concentrations of Ca (2-fold), Na (8-fold), and Si (4-fold), relative to ZTS solutions. Aluminum concentrations were dramatically reduced in PCAPS compared with ZTS samples. Differences in solution chemistry were attributed to leaching and weathering of fiberglass wicking material utilized in the PCAPS. In addition, PCAPS collected greater volumes (normalized by sampler area) of solution relative to ZTS in weak-structured sandy loam soil due to a preponderance of matrix flow. The results indicate that the PCAPS used in this study are not suitable for aqueous geochemical studies of dilute soil solutions.
• Karthikeyan, K. G., & Chorover, J. (2000). Effects of solution chemistry on the oxidative transformation of 1-naphthol and its complexation with humic acid. Environmental Science and Technology, 34(14), 2939-2946.
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  Abstract: The extent of 1-naphthol (1-hydroxynaphthalene) complexation with humic acid (HA) was studied as a function of solution chemistry [pH (4-11), ionic strength, I (0.001 and 0.1 M LiCl), and dissolved O2 (DO) concentration (0 and 8 mg L-1)] using spectroscopic (fluorescence, UV absorbance) and macroscopic (equilibrium dialysis) techniques. 1-Naphthol is transformed by DO in aqueous solutions; oxidation increases with pH and I, producing (hydroxy)naphthoquinones and coupled reaction products. Quenching of 1-naphthol fluorescence by HA increased with equilibration time from 1 to 7 d. This time-dependent relationship was found to result from (a) weak complexation of 1-naphthol by HA and (b) oxidative transformation of 1-naphthol (slow reaction) resulting in the formation of secondary products that are more reactive with HA. Sorption of 14C-labeled compound (as measured by equilibrium dialysis) followed a pH-dependent trend with minimal removal below pH 7.0, a sharp increase over a narrow pH range, and maximum retention around pH 9.0. Effects of I were observed only between pH 8 and pH 10 where a 100-fold increase in Li+ concentration doubled the extent of sorption. Good agreement between fluorescence quenching and dialysis methods was obtained. Exclusion of DO from the reaction vessel resulted in only a moderate decrease in the amount of 14C sorption, which suggests that functional groups in HA may participate directly in electron-transfer reactions with 1-naphthol.
• Majcher, E. H., Chorover, J., Bollag, J., & Huang, P. M. (2000). Evolution of CO₂ during birnessite-induced oxidation of ¹⁴C-labeled catechol. Soil Science Society of America Journal, 64(1), 157-163.
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  Abstract: Phenolic compounds undergo several transformation processes in soil and water (i.e., partial degradation, mineralization, and polymerization), many of which have been attributed primarily to biological activity. Resets from previous work indicate that naturally occurring Mn oxides are also capable of oxidizing phenolic compounds. In the present study, 14C-labeled catechol was reacted with birnessite (manganese oxide) in aqueous suspension at pH 4. The mass of catechol-derived C in solid, solution, and gas phases was quantified as a function of time. Between 5 and 16% of the total catechol C was liberated as CO2 from oxidation and abiotic ring cleavage under various conditions. Most of the 14C (55-83%) was incorporated into the solid phase in the form of stable organic reaction products whereas solution phase 14C concentrations increased from 16 to 39% with a doubling of total catechol added. Polymerization and CO2 evolution appear to be competitive pathways in the transformation of catechol since their relative importance was strongly dependent on initial birnessite-catechol reaction conditions. Solid phase Fourier transform infrared (FTIR) spectra are consistent with the presence of phenolic, quinone, and aromatic ring cleavage products. Carbon dioxide release appears to be limited by availability of reactive birnessite surface sites and it is diminished in the presence of polymerized reaction products.
• Chorover, J., Amistadi, M. K., Burgos, W. D., & Hatcher, P. G. (1999). Quinoline sorption on kaolinite-humic acid complexes. Soil Science Society of America Journal, 63(4), 850-857.
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  Abstract: Adsorption of quinoline (pK(a) = 4.92) and background electrolyte (LiCl) onto specimen kaolinite was measured as a function of surface-bound humic acid (HA) concentration (f(oc) = 0-0.5%), pH (3-10), and ionic strength (1-10 mM). Complexation of HA on the kaolinite surface (4.5 mg C kg-1) reduced the point of zero net charge (pznc) for kaolinite by more than one pH unit and resulted in a significant increase in negative surface charge. Maximum sorption of quinoline occurred near its pK(a) for all sorbents. Below the pK(a), quinoline sorption increases with increasing pH and decreasing proton competition. Above the pK(a), sorption is reduced in parallel with (but offset to a higher pH from) the ionized fraction. Competition with Li+ for surface sites is apparent from diminished quinoline adsorption with increasing ionic strength, but sorption of the ionized form of quinoline is always favored and kaolinite exhibits selectivity for cationic quinoline over Li+ (K(exc) = 65 at pH 5). However, increasing foe diminishes quinoline sorption and selectivity (K(exc) = 32 at pH 5) and increases sorption reversibility relative to uncoated kaolinite. Humic acid alone exhibits lower selectivity for quinoline (K(exc) = 4 at pH 5). The results indicate that mineral-sorbed humic substances can diminish retention of cationic quinoline despite an increase in overall cation-exchange capacity.
• Chorover, J., DiChiaro, M. J., & Chadwick, O. A. (1999). Structural charge and cesium retention in a chronosequence of tephritic soils. Soil Science Society of America Journal, 63(1), 169-177.
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  Abstract: Mineral transformation during the course of soil development is probably coupled to time-dependent trends in surface-charge and selective adsorption behavior, but the relationships are not well documented. The density of permanent (structural) charge is subject to change as a result of accretion or depletion of 2:1 layer-type silicates. The objectives of this study were to measure changes in (i) Cs+ selectivity and (ii) structural charge as affected by pedogenic mineral transformations in an age sequence of Hawaiian soils. The Cs+ → Li exchange experiments were conducted on soils collected from six sites [basaltic parent material deposited 0.3, 20, 150, 400, 1400 and 4100 thousands of years (ky) ago]. Identical exchange experiments were performed with kaolinite, montmorillonite, and illite for comparison. Selectivity for Cs+ on soils and clays increased with adsorbed mole fraction of Cs+. Cesium-accessible structural charge of the surface soils increased initially with soil age from 20 mmol(c) kg-1 at the 0.3 ky site to 113 mmol(c) kg-1 at the 400-ky site. Increased weathering beyond 400 ky reduced structural charge to 21 mmol(c) kg-1 for the oldest site. Parallel results were observed for subsurface soils with maximum structural charge of 138 mmol(c) kg-1 measured for the 400 ky site. The magnitude of Cs retention in the soils is correlated with the presence of 2:1 layer-type silicates detected by x-ray diffraction (XRD) after removal of poorly crystalline constituents. The results indicate a modest accumulation of secondary 2:1 layer-type silicates (with larger accumulations of poorly crystalline clays), followed by their subsequent decline, during the course of soil weathering.
• Karthikeyan, K. G., Chorover, J., Bortiatynski, J. M., & Hatcher, P. G. (1999). Interaction of 1-naphthol and its oxidation products with aluminum hydroxide. Environmental Science and Technology, 33(22), 4009-4015.
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  Abstract: Sterile batch experiments were conducted to investigate the effects of pH, dissolved O2 concentration, and reaction time on interaction of 0.1 mM 14C-1-hydroxynaphthalene [1-naphthol] with poorly crystalline Al(OH)3(s). Negligible (
• Karthikeyan, K. G., Elliott, H. A., & Chorover, J. (1999). Role of surface precipitation in copper sorption by the hydrous oxides of iron and aluminum. Journal of Colloid and Interface Science, 209(1), 72-78.
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  Abstract: Isotherms were developed at pH 6.9 for adsorption (ADS) and coprecipitation (CPT) of Cu by hydrous oxides of Fe (HFO) and Al (HAO) to study the role of sorbate/sorbent ratio in metal cation removal. For low sorbate/sorbent conditions, HFO had a higher Cu retention capacity than HAO regardless of contact methodology. For either oxide, CPT was consistently more effective than ADS in removing Cu from solution. At high sorbate/sorbent ratios, surface precipitation dominates and the oxide's net cation retention capacity depends on the nature and solubility of the precipitate formed at the oxide-water interface. X-ray diffraction patterns and isotherms of HAO for both ADS and CPT suggest formation of a solid solution [e.g., CuAl2O4(s)] with dramatically lower solubility than Cu(OH)2(s) precipitated in bulk solution. In contrast, Cu precipitated on the HFO surface exhibited a solubility comparable to the bulk precipitated Cu(OH)2(s). Therefore, at high sorbate/sorbent ratios, HAO has a higher Cu 'apparent' sorption capacity than HFO. The relative utility of these oxides as metal scavengers thus depends markedly on sorbate/sorbent conditions.
• Chorover, J., Zhang, J., Amistadi, M. K., & Buffle, J. (1997). Comparison of hematite coagulation by charge screening and phosphate adsorption: Differences in aggregate structure. Clays and Clay Minerals, 45(5), 690-708.
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  Abstract: The formation and structure of hematite aggregates were examined by dynamic and static light scattering techniques. A large range in coagulation kinetics was studied by varying either indifferent electrolyte (KC1) concentration or surface complexing anion (H2PO4-) concentration, PT, at pH 6.0 ± 0.1. Diffusion limited aggregation (DLA) was induced by counterion screening at [KC1] > 80 mM or by surface charge neutralization at PT = 31 μM (and ionic strength = 1.0 mM). In DLA, the fractal dimension, df, of aggregates formed by either surface charge neutralization or counterion screening was 1.7 ± 0.1. A reduction in the rate of coagulation in KC1 for [KC1] < critical coagulation concentration (CCC) produced an increase in df to 2.1 ± 0.1. For aggregation induced by phosphate adsorption at constant ionic strength, there was no apparent trend in df with coagulation rate. The value of df was consistently less than 1.8 when reaction limited aggregation (RLA) resulted from surface charge neutralization rather than counterion screening. TEM observations of aggregates formed in the presence or absence of phosphate confirm that, when RLA is induced by phosphate adsorption, resulting aggregates are much looser in structure than those formed by counterion screening. The results suggest that the high-affinity binding of phosphate to hematite may result in a nonrandom distribution of surface charge that facilitates the coalescence of positive and negative charge crystal faces.
• Chorover, J., & Sposito, G. (1995). Colloid chemistry of kaolinitic tropical soils. Soil Science Society of America Journal, 59(6), 1558-1564.
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  Abstract: Highly weathered soils of the humid tropics may exhibit loss of aggregate stability and dispersion of hydroxyl-bearing soil constituents as a result of management-induced changes in soil solution chemistry. The effects of pH and 1:1 "indifferent' electrolyte concentration on the surface charge and flocculation of colloids extracted from four representative kaolinitic tropical soils were examined by microelectrophoresis and light scattering methods. The pH and ionic strength dependence of colloidal stability observed for the soils is consistent with an electrostatic stabilization mechanism among their clay-sized particles. -Authors
• Chorover, J., & Sposito, G. (1995). Dissolution behavior of kaolinitic tropical soils. Geochimica et Cosmochimica Acta, 59(15), 3109-3121.
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  Abstract: Batch experiments at controlled pH and ionic strength were conducted with representative kaolinitic soils from Brazil to investigate their short-time dissolution behavior. The release of Al and Fe from the soils showed similar pH dependence, exhibiting a minimum value (p.m.d.) just above the point of zero net charge for the soils. Both Al and Fe release rates below the p.m.d. were correlated positively with soluble organic C, proton concentration, and net proton surface charge, the last two relationships being power-law functions similar to those observed for the dissolution rates of specimen metal oxides and aluminosilicates. Below the p.m.d., release of Si from the soils exhibited a pH dependence very much like that observed for specimen kaolinites and the molar ratios, Si Al and Fe Al released, were smaller than 1.0, probably because of the rapid solubilization of organic Al forms. Above the p.m.d., colloidal dispersion occurred and Al, Si, and Fe were released in both dissolved and microparticulate forms. © 1995.
• Chorover, J., & Sposito, G. (1995). Surface charge characteristics of kaolinitic tropical soils. Geochimica et Cosmochimica Acta, 59(5), 875-884.
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  Abstract: Surface charge properties of four representative kaolinitic soils from the humid tropics (Brazil) were investigated by a methodology involving independent measurements of net total permanent and variable charge components. Permanent structural charge was determined by Cs+ adsorption, whereas variable charge was quantified by simultaneous proton titration and background electrolyte (LiCl) adsorption measurements. Data were obtained for homoionic soils suspended in LiCl solutions of ionic strength 1-10 mmol L-1 and pH value 2-6. Corrections were made in the titration data for proton consumption resulting from dissolution and aqueous-phase complexation reactions. Conjunctive use of proton titration and electrolyte adsorption data yielded independent assessments of proton surface charge densities and points of zero charge. The surface charge data were tested successfully for consistency with the law of surface charge balance. Three of the soils exhibited similar surface charge behavior, with no pronounced effect of differences in either organic C or Fe and aluminum oxide content. One soil containing significant manganese oxides showed points of zero charge well below those of the other three soils. The point of zero net charge (p.z.n.c) for the soils was ≤4, lower than values reported for specimen kaolinite. The point of zero net proton charge (p.z.n.p.c.) increased with decreasing ionic strength. In all cases, the presence of small quantities of structural charge in 2:1 clay minerals had a significant effect on surface charge properties; e.g., for all soils, p.z.n.c. < p.z.n.p.c. These characteristics of surface charge were shown to be consistent with the behavior of a mixture of kaolinite, organic matter, and a small quantity of 2:1 clay minerals. In conformity with the law of surface charge balance, ionic strength effects were found to be removed by plotting net adsorbed ion charge against net proton surface charge density. © 1995.
• Polubesova, T. A., Chorover, J., & Sposito, G. (1995). Surface charge characteristics of Podzolized soil. Soil Science Society of America Journal, 59(3), 772-777.
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  Abstract: Recently developed methods for the accurate measurement of surface charge components and the points of zero charge in soils containing both permanent- and variable-charge constituents were applied to a Haplorthod that is typical of podzolized soils in North America, Scandinavia and Russia. Data taken across the pH range 2 to 6 tested successfully for conformity to the law of surface charge balance. Relationships between the point of zero net proton charge and the point of zero net charge were consistent with the fact that, at any pH, increasing ionic strength favored an increase in the net adsorbed ion charge, whereas changing from Cl- to SO2-4 favored a decrease in the net adsorbed ion charge. -from Authors
• Chorover, J., Vitousek, P. M., Everson, D. A., Esperanza, A. M., & Turner, D. (1994). Solution chemistry profiles of mixed-conifer forests before and after fire. Biogeochemistry, 26(2), 115-144.
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  Abstract: Solution chemistry profiles of mixed-conifer forests in granitic catchments of the Sierra Nevada were measured for three years before (1987-1990) and three years after (1990-1993) prescribed fire. Wet deposition, throughfall and soil solution samplers were installed in both white-fir and giant-sequoia dominated forest stands underlain by poorly developed inceptisols. Stream water chemistry was monitored as part of an ongoing study of catchment outputs. Calcium, NO3- and Cl- were the major ions in precipitation. Canopy leaching increased mean concentrations of all major ions, especially K+ and Ca2+. Water flux through the soil occurred largely during spring snowmelt. Forest floor leachate represented the most concentrated solutions of major ions. Interaction with the mineral soil decreased mean concentrations of most species and the average composition of soil solutions closely resembled stream water at baseflow. Bicarbonate alkalinity, Ca2+, Mg2+, and Na+ were enriched in stream water relative to precipitation whereas inputs of H+, NH4+, NO3- and SO42- were retained within the catchments. Burning of the forest understory and litter layer increased solute concentrations in soil solution and stream water. Mean soil solution Ca2+, Mg2+ and K+ concentrations increased more than 10 fold, but the relative predominance of these cations was not affected by burning. Sulfate concentration, which was very low in soil solutions of undisturbed stands (

Proceedings Publications

• Chorover, J. D., Brooks, P., Gallery, R. E., Mcintosh, J. C., Olshansky, Y., & Rasmussen, C. (2017, December). Biogeochemical control points in a water‐limited critical zone. In AGU Fall Meeting.
• Dwivedi, R., Meixner, T., Mcintosh, J. C., Ferre, P. A., Eastoe, C. J., Minor, R., Barron-Gafford, G. A., & Chorover, J. D. (2017, December). Hydrologic functioning of the deep Critical Zone and contributions to streamflow in a high elevation catchment: testing of multiple conceptual models. In AGU Fall Meeting.
• Mcintosh, J. C., White, A. M., Moravec, B. G., & Chorover, J. D. (2017, August). Changing Water, Carbon and Energy Fluxes Alters Deep CZ Structure and Solute Exports to Streams. In Goldschmidt Conference, Geochemical Society.
• Olshansky, Y., White, A. M., Thompson, M., Moravec, B. G., Mcintosh, J. C., & Chorover, J. D. (2017, December). Evolution of concentration‐discharge relations revealed by high frequency diurnal sampling of stream water during spring snowmelt. In AGU Fall Meeting.
• Sanchez, A., Meixner, T., Mcintosh, J. C., & Chorover, J. D. (2017, December). Impact of Wildfire on Solute Release in Forested Catchments, Jemez River, New Mexico, USA. In AGU Fall Meeting.
• White, A. M., Moravec, B. G., Mcintosh, J. C., & Chorover, J. D. (2017, August). Hydrologic and Environmental Controls on Uranium-Series Isotopes in a Natural Volcanic Weathering Environment. In Goldschmidt Conference, Geochemical Society.
• White, A. M., Moravec, B. G., Mcintosh, J. C., & Chorover, J. D. (2017, December). Hydrologic and environmental controls on uranium‐series and strontium isotope ratios in a natural weathering environment. In AGU Fall Meeting.

Presentations

• Chorover, J. D. (2020, Fall). Colloid and solute dynamics in the extrusive critical zone - contributions to landscape chemical denudation. Annual Meeting of the American Geophysical Union. Virtual Conference.
• Chorover, J. D. (2020, Summer). Microbial and plant effects on rock weathering and protosoil formation. Goldschmidt International Geochemistry Conference. Virtual Conference.
• Chorover, J. D., Mcintosh, J. C., Carr, B. J., Root, R. A., White, A., & Moravec, B. G. (2019, September). Resolving Critical Zone structures and weatherinf profiles across a geologically complex sub-alpine watershed. GSA Annual Meeting. Phoenix, AZ: GSA.
• Chorover, J. D., Mcintosh, J. C., White, A. M., Carr, B., Root, R. A., & Moravec, B. G. (2019, Dec). Linking near surface geophysics to critical zone architecture and biogeochemical processes. AGU Fall Meeting. San Francisco, CA: AGU.
• Chorover, J. D., Troch, P. A., Root, R. A., Amistadi, M. K., Wang, Y., & Mollaneda, J. (2019, Dec). Transport Induced Mineral Dissolution Through Intensive Hydrological Cycles in Incipient Basalt Hillslopes. AGU Fall Meeting. San Francisco, CA: AGU.
• Dontsova, K. M., Volk, M., Webb, C., Hunt, E., Tfaily, M. M., Van Haren, J. L., Sengupta, A., Chorover, J. D., Troch, P. A., & Ruiz, J. (2017, December 2017). Carbon and nitrogen accumulation and fluxes on Landscape Evolution Observatory (LEO) slopes. American Geophysical Union Fall Meeting. San Francisco, CA: American Geophysical Union.
• Maier, R. M., Chorover, J. D., Root, R. A., Gil-Loaiza, J., Neilson, J. W., & Hottenstein, J. D. (2019, Jan). Soil Microbiome Dynamics during Revegetation of Pyritic Mine Tailings: Understanding Microbial Bioindicators of Soil Acidification. SSSA International Soils Meeting. San Diego, CA: SSSA.
• Mcintosh, J. C., Olshansky, Y., Root, R. A., White, A. M., Moravec, B. G., & Chorover, J. D. (2019, Dec). Connections between shallow and deep structure of an extrusive critical zone influence hydrochemical response. AGU Fall Meeting. San Francisco, CA: AGU.
• Troch, P. A., Chorover, J. D., Toyoda, J., Chu, R. K., Hunt, E., Tfaily, M. M., & Dontsova, K. M. (2019, December 2019). B21H-2303: Spatial differences and temporal change in organic matter composition across artificial hillslope during incipient soil formation.. American Geophysical Union Fall Meeting. San Francisco, CA: American Geophysical Union.
• Chorover, J. D. (2018, August). Using big data to resolve critical zone evolution. Goldschmidt Conference 2018. Boston, MA: Goldschmidt.
• Chorover, J. D. (2018, July). Management of interdisciplinary Earth surface science data in the Critical Zone Observatory Network. Earth Science Information Partners, Annual Meeting. Tucson, AZ: Earth Science Information Partners.
• Chorover, J. D., Mcintosh, J. C., Meixner, T., & Sanchez, R. A. (2018, Fall). Impact of wildfire on solute fluxes in forested catchments, Jemez River Basin, New Mexico, USA. American Geophysical Union Fall Meeting. Washington DC.
• Chorover, J. D., Mcintosh, J. C., Meixner, T., Ferre, P. A., Sanchez, A., Olshansky, Y., Moravec, B., & White, A. (2018, Fall). THE INFLUENCE OF CRITICAL ZONE STRUCTURE ON ITS HYDROLOGIC FUNCTION: INSIGHTS INTO THE STORAGE AND ROUTING OF WATER THROUGH THE CRITICAL ZONE. Geological Society of America Conference. Indianapolis, IN.
• Chorover, J. D., Mcintosh, J. C., Moravec, B., Ma, L., & White, A. (2018, August). Combining U-Series and Sr isotopes to trace water flow through the Critical Zone. Goldschmidt Conference. Boston, MA: Geochemical Society.
• Chorover, J. D., Mcintosh, J. C., Root, R. A., White, A., & Moravec, B. (2018, Fall). DECONVOLVING LEGACY AND CONTEMPORANEOUS WEATHERING IN A PORPHYRITIC RHYOLITE AND RHYOLITIC TUFF DOMINATED UPLAND CATCHMENT, VALLES CALDERA, NEW MEXICO. Geological Society of America Conference. Indianapolis, IN.
• Chorover, J. D., Stanley, M., Mitra, B., Abramson, N., Barron-Gafford, G. A., Knowles, J., Minor, R., Niu, G., Wright, W., Castro, C. L., Eastoe, C., Ferre, P. A., Mcintosh, J. C., Meixner, T., & Dwivedi, R. (2018, Fall). An improved and practical approach for estimating catchment-scale response functions through power spectral analysis. American Geophysical Union Fall Meeting. Washington DC.
• Chorover, J. D. (2017, April). “Biogeochemical transformation of metal(loid)s in a disturbed critical zone”.. Annual Spring Meeting. San Francisco, CA: American Chemical Society.
• Chorover, J. D. (2017, April). “Biogeochemistry of the semi-arid critical zone”.. Biogeochemistry and Environmental Science and Sustainability Seminar Series. Ithaca, NY: Cornell University.
• Chorover, J. D. (2017, December). “Biogeochemical control points in a water-limited critical zone”.. American Geophysical Union Annual Meeting. New Orleans, LA: AGU.
• Chorover, J. D. (2017, October). “Soil chemical transformations affect arsenic bioaccessibility during mine tailings diagenesis”.. Symposium on Soil Chemistry, Food Security and Human Health. Tampa, FL: Soil Science Socity of America.
• Dontsova, K. M., Bonine, K. E., Batchelor, R. L., Brinkworth, C., Keller, J. M., Hogan, D., & Treloar, D. (2017, December 2017). Biosphere 2, a nexus of partner networks that improve student experiences and outcomes. American Geophysical Union Fall Meeting. San Francisco, CA: American Geophysical Union.
• Ruiz, J., Troch, P. A., Chorover, J. D., Sengupta, A., Van Haren, J. L., Tfaily, M. M., Hunt, E., Webb, C., Volk, M., & Dontsova, K. M. (2017, December 2017). Carbon and nitrogen accumulation and fluxes on Landscape Evolution Observatory (LEO) slopes. American Geophysical Union Fall Meeting. San Francisco, CA: American Geophysical Union.
• Troch, P. A., Zeng, X., Wang, Y., Van Haren, J. L., Tuller, M., Sibayan, M., Schaap, M. G., Saleska, S. R., Ruiz, J., Rasmussen, C., Pelletier, J. D., Niu, G., Monson, R. K., Meredith, L., Alves Meira Neto, A., Matos, K. A., Maier, R. M., Kim, M., Hunt, E. A., , Harman, C. J., et al. (2017, December). Controlled Experiments of Hillslope Co-evolution at the Biosphere 2 Landscape Evolution Observatory: Toward Prediction of Coupled Hydrological, Biogeochemical, and Ecological change. AGU International Annual Meeting. New Orleans, LA: American Geophysical Union (AGU).
• Volkmann, T. H., Sengupta, A., Pangle, L. A., Abramson, N., Barron-Gafford, G. A., Breshears, D. D., Bugaj, A., Chorover, J. D., Dontsova, K. M., Durcik, M., Ferre, P. A., Harman, C. J., Hunt, E. A., Kim, M., Maier, R. M., Matos, K. A., Alves Meira Neto, A., Meredith, L., Monson, R. K., , Niu, G., et al. (2017, December). Controlled Experiments of Hillslope Co-evolution at the Biosphere 2 Landscape Evolution Observatory: Toward Prediction of Coupled Hydrological, Biogeochemical, and Ecological change. AGU International Annual Meeting. New Orleans, LA: American Geophysical Union (AGU).
• Bryan, M., Alyssa, W., Ben, P., Andres, S., Dawson, F., Mcintosh, J. C., Pelletier, J. D., Gallery, R. E., Rasmussen, C., & Chorover, J. D. (2016, Winter). Coring the deep Critical Zone in the Jemez River Basin Critical Zone. 2016 American Geophysical Union Annual Meeting. San Francisco CA: American Geophysical Union.
• Dawson, F., Christopher, S., Margretta, M., Rasmussen, C., Chorover, J. D., Virginia, R., & Gallery, R. E. (2016, July). Microbial biogeochemistry at the Jemez River Basin Critical Zone Observatory. Invited Speaker: Aqua Diva CZO. Jena, Germany. Jena, Germany: Jena, Germany.
• Dwivedi, R., Meixner, T., Mcintosh, J. C., Ferre, P. A., & Chorover, J. D. (2016, Fall). A multi-tracer approach coupled to numerical models to improve understanding of mountain block processes in a high elevation, semi-humid catchment. Geological Society of America (GSA) Annual Meeting. Denver, CO.
• Mcintosh, J. C., Xavier, Z., Rasmussen, C., Paul, B. D., Gallery, R. E., Pelletier, J. D., & Chorover, J. D. (2016, Winter). Changing Energy Inputs at Earth’s Surface Translates to Differences in Water Availability, Weathering Rates, and Biotic Activity at Depth. 2016 American Geophysical Union Annual Meeting, Union Session. San Francisco CA: American Geophysical Union.
• Mcintosh, J. C., Xavier, Z., Rasmussen, C., Paul, B. D., Gallery, R. E., Pelletier, J. D., & Chorover, J. D. (2016, Winter). Changing Energy Inputs at Earth’s Surface Translates to Differences in Water Availability, Weathering Rates, and Biotic Activity at Depth. 2016 American Geophysical Union Annual Meeting. San Francisco CA: American Geophysical Union.
• Chorover, J. (2015, March). Carbon and contaminants in the critical zone. Invited keynote presentation.. American Chemical Society National Meetings. Denver, CO.
• Chorover, J. D. (2015, December). Biogeochemical transformation of metal(loid)s in mine tailings. Department of Geological Sciences Colloquium Series. University of Texas at El Paso: Department of Geological Sciences.
• Chorover, J. D. (2015, December). Influence of organic matter-mineral interfacial reactions on arsenic speciation and bioaccessibility. Annual Meeting of the American Geophysical Union. San Francisco, CA: AGU.
• Chorover, J. D. (2015, December). What makes the global CZO network greater than the sum of its parts?. International CZO Workshop, Annual Meeting of the American Geophysical Union. San Francisco, CA: AGU.
• Chorover, J. D. (2015, February). Evolution of bio-inorganic interfaces in the critical zone: Impacts of carbon and water throughflux. CSIRO Seminar Series. Adelaide, Brisbane, and Canberra, Australia: CSIRO.
• Chorover, J. D. (2015, September). Earth's critical zone: The layer that sustains life. Science Cafe Series. UA: College of Science.
• Dontsova, K. M., Huxman, T. E., Chorover, J. D., Maier, R. M., Zaharescu, G. D., & Burghelea, C. (2015, November). Grass and microbiota effect on lithogenic element mobilization during weathering of basalt, granite, rhyolite, and schist. Geological Society of America annual meeting. Baltimore, MD: Geological Society of America.
• Chorover, J. (2014, February). Critical zone evolution by jerks: Impacts of carbon and water through-flux. Distinguished Scientist Seminar Series, Lawrence Berkeley National Laboratory. Berkeley CA: Lawrence Berkeley National Laboratory.
• Chorover, J. (2014, June). Soil biogeochemical processes in the critical zone. 20th World Congress of Soil Science. Jeju, South Korea.
• Chorover, J. (2014, March). Soil carbon (de)stabilization under changing climate: Scaling from micropores to catchments.. Symposium on Biogeochemistry of Earth System Models, American Chemical Society Annual Meetings. Dallas, TX.
• Chorover, J. (2014, May). Carbon and contaminants in the critical zone. Invited keynote presentation.. Division of Biological and Environmental Sciences, Department of Energy, Workshop on Environmental Molecular Sciences. Germantown, MD.
• Chorover, J. (2014, November). Soil carbon (de)stabilization under changing climate: Scaling from micropores to catchments.. Soil Science Society of America Annual Meetings. Long Bearch,CA.
• Chorover, J. D. (2014, June). Combining advanced analytical methods to assess interfacial change during bioweathering of silicates and sulfates. Keynote Presenation, 20th World Congress of Soil Science. Jeju, South Korea.
• Chorover, J. D., Chorover, J. D., Pelletier, J. D., Pelletier, J. D., Breshears, D. D., Breshears, D. D., Mcintosh, J. C., Mcintosh, J. C., Rasmussen, C., Rasmussen, C., Brooks, P. D., Brooks, P. D., Barron-Gafford, G. A., Barron-Gafford, G. A., Gallery, R. E., Gallery, R. E., Ferre, P. A., Ferre, P. A., Meixner, T., , Meixner, T., et al. (2014, September). The Catalina-Jemez CZO: Transformative Behavior of Energy, Water and Carbon in the Critical Zone II. Interactions between Long and Short Term Processes that Control Delivery of Critical Zone Services.. National Critical Zone Observatory All-Hands Meeting.
• Chorover, J. D., Huxman, T. E., Maier, R. M., Burghelea, C., Dontsova, K. M., & Zaharescu, D. (2014, December). Cracking the Code of Soil Genesis. The Early Role of Rare Earth Elements. American Geophysical Union (AGU) Fall Meeting. San Francisco, CA.
• Ruiz, J., Barron-Gafford, G. A., Van Haren, J. L., Dontsova, K. M., Troch, P. A., & Chorover, J. D. (2014, December). Rapid CO2 consumption during incipient weathering of a granular basaltic hillslope in the Landscape Evolution Observatory, Biosphere 2.. American Geophysical Union’s Annual Fall Meeting.
• Zaharescu, D., Dontsova, K. M., Burghelea, C., Maier, R. M., Huxman, T. E., & Chorover, J. D. (2014, December). Cracking the Code of Soil Genesis. The Early Role of Rare Earth Elements. 2014 American Geophysical Union (AGU) Fall Meeting. San Francisco, CA.
• Chorover, J. (2013, August). Critical zone evolution by jerks. Keynote Lecture, Goldschmidt Geochemistry Conference Symposium 16b. Florence, Italy.
• Chorover, J. D. (2013, August). Critical zone evolution by jerks. Keynote presentation, Symposium on Critical Zone Biogeochemistry, Goldschmidt International Geochemistry Conference. Florence, Italy: Goldschmidt Geochemistry Conference Symposium.
• Chorover, J. D. (2012, November). Critical Zone Observatories for Sustainable Soil Development and Beyond. 2nd International Conference of Geobiology. Wuhan, China: China University of Geosciencs.
• Chorover, J. D. (2012, November). Integrating measurements and models of Earth surface processes to improve prediction of landscape structure, function and evolution. American Geophysical Union (AGU) Conference. San Francisco, CA.
• Chorover, J. D. (2012, November). Quantifying Water, Carbon and Energy as Process Drivers of Critical Zone Evolution.. Life Depends on Soil, Water, & Climate - Special Seminar Series.
• Chorover, J. D. (2012, September). Environmental Chemistry. SWES 195 Careers in Environmental Science: Tom Wilson, instructor. UA Campus.
• Chorover, J. D. (2011, November). Biogeochemical reactions in beakers, pores, columns and hillslopes. Hydrology and Water Resources Seminar Series. Tucson, AZ.
• Chorover, J. D. (2011, November). Plant-microbe-mineral-organic interactions in the Critical Zone. Goldschmidt Geochemistry Conference Symposium 17b: Where Minerals Meet Life: Organic Matter Turnover in the Critical Zone. Prague, Czech Republic.
• Chorover, J. D. (2011, November). The Jemez Santa Catalina Critical Zone Observatory: Transformative behavior of water, energy and carbon in the Critical Zone. CUAHSI Webinar Series on Environmental Observatories.
• Chorover, J. D. (2011, September). Environmental Chemistry. SWES 195 Careers in Environmental Science : Tom Wilson, instructor. UA Campus.

Poster Presentations

• Chorover, J. D., Amistadi, M. K., Barrientes, D., & Abrell, L. M. (2021, October). Total organic fluorine analysis for total PFAS mass estimate – by combustion ion chromatography. American Chemical Society Rocky Mountain Regional Meeting, Oct 20-23, 2021. Tucson, AZ USA: American Chemical Society.
• Meredith, L., Troch, P. A., Maier, R. M., Chorover, J. D., Neilson, J. W., Dontsova, K. M., Volkmann, T., Stegen, J., Barberan, A., & Sengupta, A. (2018, August). Structural and functional response of incipient basaltic microbial community to shifts in soil moisture regime. Goldschmidt. Boston, MA.
• Meredith, L., Troch, P. A., Maier, R. M., Chorover, J. D., Neilson, J. W., Dontsova, K. M., Volkmann, T., Stegen, J., Barberan, A., & Sengupta, A. (2019, January). Structural and Functional Response of Microbial Community in an Oligotrophic Basalt Soil System to Shifts in Rainfall Regimes. Soil Science Society of America (SSSA) International Soils Meeting “Soils Across Latitudes”. San Diego, CA: Soil Science Society of America.
• Reinhard, C., Chorover, J. D., Dontsova, K. M., Burghelea, C., Szeinbaum, N., & Zaharescu, G. D. (2018, August). Oxidative Biological Weathering and its Archean Origins. Goldschmidt. Boston, MA.
• Troch, P. A., Chorover, J. D., Harman, C., Dontsova, K. M., Meredith, L., Wang, Y., Sengupta, A., Meira Neto, A., Matos, K., Hunt, E., Bugaj, A., Abramson, N., Volkmann, T., & Kim, M. (2018, December). H13N-1958 Experimental observation of a hillslope-scale rank StorAge Selection function: Process controls on its functional form, time variability, and hysteresis.. American Geophysical Union fall meeting. Washington, DC: American Geophysical Union.
• Troch, P. A., Chorover, J. D., Hunt, E., Dontsova, K. M., Wang, Y., & Hitzelberger, M. (2018, August). Coupling Hydrologic Processes and Geochemical Weathering Patterns in a Fully Controlled Basaltic Soil Lysimeter. 2018 Undergraduate Research Opportunities Consortium (UROC) symposium. Tucson, AZ: UA Graduate college.
• Troch, P. A., Chorover, J. D., Hunt, E., Dontsova, K. M., Wang, Y., & Hitzelberger, M. (2018, December). ED13E-0792: Coupling Hydrologic Processes and Geochemical Weathering Patterns in a Fully Controlled Basaltic Soil Lysimeter. American Geophysical Union fall meeting. Washington, DC: American Geophysical Union.
• Troch, P. A., Zeng, X., Wang, Y., Van Haren, J. L., Tuller, M., Sibayan, M., Schaap, M. G., Saleska, S. R., Ruiz, J., Rasmussen, C., Pelletier, J. D., Niu, G., Monson, R. K., Meredith, L., Alves Meira Neto, A., Matos, K. A., Maier, R. M., Kim, M., Hunt, E. A., , Harman, C. J., et al. (2017, December). Controlled Experiments of Hillslope Co-evolution at the Biosphere 2 Landscape Evolution Observatory: Toward Prediction of Coupled Hydrological, Biogeochemical, and Ecological change. 2017 AGU Fall Meeting, Abstract B43A-2105. New Orleans, LA: American Geophysical Union (AGU).
  More info

  Understanding the process interactions and feedbacks among water, microbes, plants, and porous geological media is crucial for improving predictions of the response of Earth’s critical zone to future climatic conditions. However, the integrated co-evolution of landscapes under change is notoriously difficult to investigate. Laboratory studies are typically limited in spatial and temporal scale, while field studies lack observational density and control. To bridge the gap between controlled lab and uncontrolled field studies, the University of Arizona – Biosphere 2 built a macrocosm experiment of unprecedented scale: the Landscape Evolution Observatory (LEO). LEO consists of three replicated, 330-m2 hillslope landscapes inside a 5000-m2 environmentally controlled facility. The engineered landscapes contain 1-m depth of basaltic tephra ground to homogenous loamy sand that will undergo physical, chemical, and mineralogical changes over many years. Each landscape contains a dense sensor network capable of resolving water, carbon, and energy cycling processes at sub-meter to whole-landscape scale. Embedded sampling devices allow for quantification of biogeochemical processes, and facilitate the use of chemical tracers applied with the artificial rainfall. LEO is now fully operational and intensive forcing experiments have been launched. While operating the massive infrastructure poses significant challenges, LEO has demonstrated the capacity of tracking multi-scale matter and energy fluxes at a level of detail impossible in field experiments. Initial sensor, sampler, and restricted soil coring data are already providing insights into the tight linkages between water flow, weathering, and (micro-) biological community development during incipient landscape evolution. Over the years to come, these interacting processes are anticipated to drive the model systems to increasingly complex states, potentially perturbed by changes in climatic forcing. By intensively monitoring the evolutionary trajectory, integrating data with models, and fostering community-wide collaborations, we envision that emergent landscape structures and functions can be linked and significant progress can be made toward predicting the coupled hydro-biogeochemical and ecological responses to global change.
• Volkmann, T. H., Troch, P. A., Sengupta, A., Zeng, X., Pangle, L. A., Wang, Y., Abramson, N., Van Haren, J. L., Tuller, M., Barron-Gafford, G. A., Breshears, D. D., Sibayan, M., Bugaj, A., Schaap, M. G., Saleska, S. R., Chorover, J. D., Ruiz, J., Dontsova, K. M., Rasmussen, C., , Durcik, M., et al. (2017, December). Controlled Experiments of Hillslope Co-evolution at the Biosphere 2 Landscape Evolution Observatory: Toward Prediction of Coupled Hydrological, Biogeochemical, and Ecological change. AGU International Annual Meeting. New Orleans, LA: American Geophysical Union (AGU).
• Bryan, M., Alyssa, W., Ben, P., Andres, S., Dawson, F., Mcintosh, J. C., Pelletier, J. D., Gallery, R. E., Rasmussen, C., & Chorover, J. D. (2016, Winter). Coring the deep Critical Zone in the Jemez River Basin Critical Zone. 2016 American Geophysical Union Annual Meeting. San Francisco CA: American Geophysical Union.
• Dawson, F., Chelsea, C., Chorover, J. D., Virginia, R., & Gallery, R. E. (2016, Winter). Microbial community recovery post-fire in a high elevation mixed conifer catchment in response to varied precipitation regime. 2016 American Geophysical Union Annual Meeting. San Francisco CA: American Geophysical Union.
• Troch, P. A., Chorover, J. D., Dontsova, K. M., Wang, Y., & Umanzor, M. (2016, December 2016). A Centimeter‐Scale Investigation of Geochemical Hotspots in a Soil Lysimeter. American Geophysical Union Fall Meeting. San Francisco, CA: American Geophysical Union.
• Murphy, M., Fairbanks, D., Chorover, J. D., Rich, V., & Gallery, R. E. (2014, December). Impact of Wildfire on Microbial Biomass in the Critical Zone Observatory.. American Geophysical Union (AGU). San Francisco, CA: AGU.
• Rich, V., Fairbanks, D., Murphy, M., Frost, G., Chorover, J. D., & Gallery, R. E. (2014, December). Impact of fire, landscape position and soil depth on extracellular enzyme activities at the Jemez River Basin Critical Zone Observatory.. American Geophysical Union (AGU). San Francisco, CA: AGU.
• Troch, P. A., Dontsova, K. M., Chorover, J. D., Niu, Y., & Wu, R. (2014, December). Reactive Transport Modelling of Mineral Evolution in the Biosphere 2 Hillslope Experiment. American Geophysical Union (AGU) Fall Meeting. San Francisco, CA.
• Wu, R., Niu, Y., Chorover, J. D., Dontsova, K. M., & Troch, P. A. (2014, December). Reactive Transport Modelling of Mineral Evolution in the Biosphere 2 Hillslope Experiment. 2014 American Geophysical Union (AGU) Fall Meeting. San Francisco, CA.
• Breshears, D. D., Field, J. P., Law, D. J., Brooks, P. D., Chorover, J., Pelletier, J. D., Troch, P. A., Lopez Hoffman, L., Rasmussen, C., Papuga, S. A., Barron-Gafford, G. A., Mcintosh, J. C., Harpold, A., Biederman, J. A., & Litvak, M. (2013, October 2013). Bridging from soil to ecosystem goods and services provided by the Critical Zone. AGU Chapman Conference: Soil-mediated drivers of coupled biogeochemical and hydrological processes across scales. Tucson.
• Schaap, M. G., Kopp, E. S., Pohlman, M. A., Jones, C. A., & Chorover, J. (2013, December). Pre- and Post-Fire Infiltration Rates in a Montane Mixed Conifer Ecosystem. AGU Fall meeting 2013. San Fancisco: AGU (poster: NSF-CZO).

Others

• Chorover, J. D., Druhan, J., McDowell, W. H., & Derry, L. (2017, December). Concentration-discharge relations in the critical zone.. Co-organizer and Convener for Annual Meeting of the American Geophysical Union.