Edward P Glenn

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• Nagler, P. L., Pearlstein, S., Glenn, E. P., Brown, T. B., Bateman, H. L., Bean, D. W., & Hultine, K. R. (2014). Rapid dispersal of saltcedar (Tamarix spp.) biocontrol beetles (Diorhabda carinulata) on a desert river detected by phenocams, MODIS imagery and ground observations. Remote Sensing of Environment, 140, 206-219.
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  Abstract: We measured the rate of dispersal of saltcedar leaf beetles (Diorhabda carinulata), a defoliating insect released on western rivers to control saltcedar shrubs (Tamarix spp.), on a 63km reach of the Virgin River, U.S. Dispersal was measured by satellite imagery, ground surveys and phenocams. Pixels from the Moderate Resolution Imaging Spectrometer (MODIS) sensors on the Terra satellite showed a sharp drop in NDVI in midsummer followed by recovery, correlated with defoliation events as revealed in networked digital camera images and ground surveys. Ground surveys and MODIS imagery showed that beetle damage progressed downstream at a rate of about 25kmyr-1 in 2010 and 2011, producing a 50% reduction in saltcedar leaf area index and evapotranspiration by 2012, as estimated by algorithms based on MODIS Enhanced Vegetation Index values and local meteorological data for Mesquite, Nevada. This reduction is the equivalent of 10.4% of mean annual river flows on this river reach. Our results confirm other observations that saltcedar beetles are dispersing much faster than originally predicted in pre-release biological assessments, presenting new challenges and opportunities for land, water and wildlife managers on western rivers. Despite relatively coarse resolution (250m) and gridding artifacts, single MODIS pixels can be useful in tracking the effects of defoliating insects in riparian corridors. © 2013.
• Bateman, H. L., Nagler, P. L., & Glenn, E. P. (2013). Plot- and landscape-level changes in climate and vegetation following defoliation of exotic saltcedar (Tamarix sp.) from the biocontrol agent Diorhabda carinulata along a stream in the Mojave Desert (USA). Journal of Arid Environments, 89, 16-20.
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  Abstract: The biocontrol agent, northern tamarisk beetle (Diorhabda carinulata), has been used to defoliate non-native saltcedar (Tamarix spp.) in USA western riparian systems since 2001. Biocontrol has the potential to impact biotic communities and climatic conditions in affected riparian areas. To determine the relationships between biocontrol establishment and effects on vegetation and climate at the plot and landscape scales, we measured temperature, relative humidity, foliage canopy, solar radiation, and used satellite imagery to assess saltcedar defoliation and evapotranspiration (ET) along the Virgin River in the Mojave Desert. Following defoliation solar radiation increased, daily humidity decreased, and maximum daily temperatures tended to increase. MODIS and Landsat satellite imagery showed defoliation was widespread, resulting in reductions in ET and vegetation indices. Because biocontrol beetles are spreading into new saltcedar habitats on arid western rivers, and the eventual equilibrium between beetles and saltcedar is unknown, it is necessary to monitor trends for ecosystem functions and higher trophic-level responses in habitats impacted by biocontrol. © 2012 Elsevier Ltd.
• Bresloff, C. J., Nguyen, U., Glenn, E. P., Waugh, J., & Nagler, P. L. (2013). Effects of grazing on leaf area index, fractional cover and evapotranspiration by a desert phreatophyte community at a former uranium mill site on the Colorado Plateau. Journal of Environmental Management, 114, 92-104.
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  PMID: 23220605;Abstract: This study employed ground and remote sensing methods to monitor the effects of grazing on leaf area index (LAI), fractional cover (fc) and evapotranspiration (ET) of a desert phreatophyte community over an 11 year period at a former uranium mill site on the Colorado Plateau, U.S. Nitrate, ammonium and sulfate are migrating away from the mill site in a shallow alluvial aquifer. The phreatophyte community, consisting of Atriplex canescens (ATCA) and Sarcobatus vermiculatus (SAVE) shrubs, intercepts groundwater and could potentially slow the movement of the contaminant plume through evapotranspiration (ET). However, the site has been heavily grazed by livestock, reducing plant cover and LAI. We used livestock exclosures and revegetation plots to determine the effects of grazing on LAI, fc and ET, then projected the findings over the whole site using multi-platform remote sensing methods. We show that ET is approximately equal to annual precipitation at the site, but when ATCA and SAVE are protected from grazing they can develop high fc and LAI values, and ET can exceed annual precipitation, with the excess coming from groundwater discharge. Therefore, control of grazing could be an effective method to slow migration of contaminants at this and similar sites in the western U.S. © 2012 Elsevier Ltd.
• Brown, J. J., Limburg, K. E., Waldman, J. R., Stephenson, K., Glenn, E. P., Juanes, F., & Jordaan, A. (2013). Fish and hydropower on the U.S. Atlantic coast: failed fisheries policies from half-way technologies. Conservation Letters, 6(4), 280-286.
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  Abstract: Globally, diadromous species are at risk from fragmentation by damming of rivers, and a host of other anthropogenic factors. On the United States Atlantic Coast, where diadromous fish populations have undergone dramatic declines, restoration programs based on fishway construction and hatcheries have sustained remnant populations, but large-scale restoration has not been achieved. We examine anadromous fish restoration programs on three large Atlantic Coast rivers, the Susquehanna, Connecticut, and Merrimack with multiple mainstem hydropower dams, most with relatively low generating capacity. Mean passage efficiencies through fishways on these rivers from the first dam to the spawning grounds for American shad are less than 3%. The result is that only small fractions of targeted fish species are able to complete migrations. It may be time to admit failure of fish passage and hatchery-based restoration programs and acknowledge that significant diadromous species restoration is not possible without dam removals. The approach being employed on the Penobscot River, where dams are being removed or provided the opportunity to increase power generation within a plan to provide increased access to habitat, offers a good model for restoration. Dammed Atlantic Coastal rivers offer a cautionary tale for developing nations intent on hydropower development, suggesting that lasting ecosystem-wide impacts cannot be compensated for through fish passage and hatchery technology. ©2013 Wiley Periodicals, Inc.
• Carrillo-Guerrero, Y., Glenn, E. P., & Hinojosa-Huerta, O. (2013). Water budget for agricultural and aquatic ecosystems in the delta of the Colorado River, Mexico: Implications for obtaining water for the environment. Ecological Engineering, 59, 41-51.
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  Abstract: In arid lands, wetland loss is the result not only of the scarcity of water itself, but also of the management of water to maximize off-stream uses. In the Colorado River delta, Mexico, no in-stream flows are allocated for aqutic ecocystems, yet agricultural return flows and canal operational releases support 36,377ha of valuable wetland and riparian habitat. We evaluated the relationships between water use in the Mexicali Irrigation District (DR014) and the water supply for the Colorado River delta wetlands. Mexicali farmers applied on average 1024mmyr-1 to fields in 2008, less than half of what is applied to irrigated fields in a typical irrigation district in the U.S. portion of the river. Farm-level agricultural efficiency is high, as 90% of water applied to fields can be accounted for in evapotranspiration (ET), as estimated by a remote sensing technique and by a district water budget approach. By contrast, in a comparison U.S. irrigation district, ET accounts for only 60% of applied water and the rest emerges as irrigation return flows. Despite the apparent high on-farm irrigation efficiency in DR014, sufficient water is discharged to support valuable ecosystems. Seepage losses from canals are higher than in the comparison district in the U.S., and this water contributes to formation of a high, non-saline aquifer that supported riparian trees along the river. On the other hand, surface drainage water supports brackish wetland habitats south of the irrigation district. The goal of obtaining water for environmental uses by increasing agricultural efficiency in the irrigation districts would not by itself be an effective strategy for the delta aquatic habitats as the delta wetlands and riparian areas are currently dependent on canal seepage, return flows and waste spills from both the U.S. and Mexico. © 2013 Elsevier B.V.
• Doody, T. M., Glenn, E. P., & Benyon, R. G. (2013). Transpiration and stomatal conductance trends in riparian vegetation. Acta Horticulturae, 991, 171-180.
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  Abstract: Exotic species continue to pose ecological problems globally. Within dynamic riverine aquatic systems, invasive woody vegetation often displaces native species or inhabits otherwise unoccupied habitats, increasing total riparian leaf area and riparian evaporative losses. Concern over implications to water resources and altered aquatic ecology has instigated field studies in southeastern Australia to quantify water use of riparian invasive Salix babylonica, Salix fragilis and native Eucalyptus camaldulenis. Spatial, temporal and species variability in transpiration and stomatal regulation were investigated using hourly sap flow measurements. We demonstrate that continuous long-term sap flow data sets can provide new insights into the hydraulic functioning of Salix spp., improving our understanding of willow water use. Wide variability in transpiration occurs across study locations, seasons, within species and with hydrological setting as stream fluctuation leads to reduced Salix transpiration, indicating a strong sensitivity to flow variability. Complex seasonal patterns of stomatal conductance (GS) and leaf level transpiration (EL) are shown for both Salix and Eucalyptus in both water limited and unlimited environments. Within both settings, Salix and Eucalyptus exhibit summer mid-day depressions in GS, with peak G S occurring before 10 am. The relationship between vapour pressure density (VPD), GS and EL yielded VPD thresholds of 3 kPa for Salix stands located within stream beds in a semi-arid climate and Eucalyptus located on both dry and saturated banks after which increasing stomatal turgor constrained transpiration, possibly to prevent xylem cavitation. A threshold of 2 kPa was identified for S. babylonica located on stream banks and S. fragilis located in-stream. Collectively, the results derived from sap flow data may provide future management options such as river height manipulation to reduce evaporative losses from Salix in Australia. © ISHS 2013.
• Glenn, E. P., Anday, T., Chaturvedi, R., Martinez-Garcia, R., Pearlstein, S., Soliz, D., Nelson, S. G., & Felger, R. S. (2013). Three halophytes for saline-water agriculture: An oilseed, a forage and a grain crop. Environmental and Experimental Botany, 92, 110-121.
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  Abstract: Greenhouse and field trials and nutritional studies are reviewed for three halophytes that are candidate species for salt-water crop production. Salicornia bigelovii is a leafless, C3, succulent annual salt marsh plant that produces an oilseed on seawater irrigation in coastal desert environments. Yields on seawater are similar to conventional oilseeds under ideal conditions but are reduced under mechanical harvest due to uneven seed ripening and shattering of seeds. Water management requires frequent irrigation to keep the shallow-root zone at field capacity and to ensure a leaching fraction to prevent accumulation of salts. Nutritional value of oil, seed meal and biomass are adequate to replace conventional animal feed ingredients in formulated diets, despite presence of saponins in the meal and high salt content of the biomass. A breeding program showed that this species is amendable to improvement using conventional breeding approaches. Atriplex lentiformis is a perennial C4 xerohalophyte shrub valued as a forage species in North American rangelands. Under cultivation it produces as much biomass and protein as alfalfa on salinities ranging from mildly saline (1.8gL-1 TDS) to full seawater salinity (40gL-1). Greenhouse trials show that salinity increases dry matter production and water use efficiency of A. lentiformis on drying soils, making it a good candidate for deficit irrigation for forage production. As with other Atriplex spp., its crop potential is currently limited by a tendency to become woody with successive cuts and with non-protein nitrogen and anti-nutritional compounds present in leaves. Distichlis palmeri is a perennial C4 saltgrass endemic to the delta of the Colorado River in the northern Gulf of California that produces a grain similar in size and nutrition composition to rice. It was a staple summer food source for the Cocopa people before upstream water diversions disrupted flood flows to the delta. It is productive on full-strength seawater and produces aerenchyma tissue allowing it to grow under flooded conditions similar to paddy rice. However, only limited experiments have been conducted with this plant, and therefore its ultimate agronomic potential is unknown. Despite initial pessimism about the production potential of halophytes, these examples show that euhalophytes can maintain high productivity of useful agricultural products up to a root-zone salinity of 70gL-1 TDS, double the salinity of seawater. © 2012 Elsevier B.V.
• Glenn, E. P., Mexicano, L., Garcia-Hernandez, J., Nagler, P. L., Gomez-Sapiens, M. M., Tang, D., Lomeli, M. A., Ramirez-Hernandez, J., & Zamora-Arroyo, F. (2013). Evapotranspiration and water balance of an anthropogenic coastal desert wetland: Responses to fire, inflows and salinities. Ecological Engineering, 59, 176-184.
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  Abstract: Evapotranspiration (ET) and other water balance components were estimated for Cienega de Santa Clara, an anthropogenic brackish wetland in the delta of the Colorado River in Mexico. The marsh is in the Biosphere Reserve of the Upper Gulf of California and Delta of the Colorado River, and supports a high abundance and diversity of wildlife. Over 95% of its water supply originates as agricultural drain water from the USA, sent for disposal in Mexico. This study was conducted from 2009 to 2011, before, during and after a trial run of the Yuma Desalting Plant in the USA, which will divert water from the wetland and replace it with brine from the desalting operation. The goal was to estimate the main components in the water budget to be used in creating management scenarios for this marsh. We used a remote sensing algorithm to estimate ET from meteorological data and Enhanced Vegetation Index values from the Moderate Resolution Imaging Spectrometer (MODIS) sensors on the Terra satellite. ET estimates from the MODIS method were then compared to results from a mass balance of water and salt inflows and outflows over the study period. By both methods, mean annual ET estimates ranged from 2.6 to 3.0mmd-1, or 50 to 60% of reference ET (ETo). Water entered at a mean salinity of 2.6gL-1 TDS and mean salinity in the wetland was 3.73gL-1 TDS over the 33 month study period. Over an annual cycle, 54% of inflows supported ET while the rest exited the marsh as outflows; however, in winter when ET was low, up to 90% of the inflows exited the marsh. An analysis of ET estimates over the years 2000-2011 showed that annual ET was proportional to the volume of inflows, but was also markedly stimulated by fires. Spring fires in 2006 and 2011 burned off accumulated thatch, resulting in vigorous growth of new leaves and a 30% increase in peak summer ET compared to non-fire years. Following fires, peak summer ET estimates were equal to ETo, while in non-fire years peak ET was equal to only one-half to two-thirds of ETo. Over annual cycles, estimated ET was always lower than ETo, because T. domingensis is dormant in winter and shades the water surface, reducing direct evaporation. Thus, ET of a Typha marsh is likely to be less than an open water surface under most conditions. © 2012 Elsevier B.V.
• Glenn, E. P., Nagler, P. L., Morino, K., & Hultine, K. R. (2013). Erratum to: Phreatophytes under stress: Transpiration and stomatal conductance of saltcedar (Tamarix spp.) in a high-salinity environment (Plant Soil, 10.1007/s11104-013-1803-0). Plant and Soil, 371(1-2), 673-.
• Glenn, E. P., Nagler, P. L., Morino, K., & Hultine, K. R. (2013). Phreatophytes under stress: Transpiration and stomatal conductance of saltcedar (Tamarix spp.) in a high-salinity environment. Plant and Soil, 371(1-2), 655-672.
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  Abstract: Background and aims: We sought to understand the environmental constraints on an arid-zone riparian phreatophtye, saltcedar (Tamarix ramosissima and related species and hybrids), growing over a brackish aquifer along the Colorado River in the western U.S. Depth to groundwater, meteorological factors, salinity and soil hydraulic properties were compared at stress and non-stressed sites that differed in salinity of the aquifer, soil properties and water use characteristics, to identify the factors depressing water use at the stress site. Methods: Saltcedar leaf-level transpiration (EL), LAI, and stomatal conductance (GS) were measured over a growing season (June-September) with Granier and stem heat balance sensors and were compared to those for saltcedar at the non-stress site determined in a previous study. Transpiration on a ground-area basis (EG) was calculated as EL × LAI. Environmental factors were regressed against hourly and daily EL and GS at each site to determine the main factors controlling water use at each site. Results: At the stress site, mean EG over the summer was only 30 % of potential evapotranspiration (ETo). GS and EG peaked between 8 and 9 am then decreased over the daylight hours. Daytime GS was negatively correlated with vapor pressure deficit (VPD) (P < 0.05). By contrast, EG at the non-stress site tracked the daily radiation curve, was positively correlated with VPD and was nearly equal to ETo on a daily basis. Depth to groundwater increased over the growing season at both sites and resulted in decreasing EG but could not explain the difference between sites. Both sites had high soil moisture levels throughout the vadose zone with high calculated unsaturated conductivity. However, salinity in the aquifer and vadose zone was three times higher at the stress site than at the non-stress site and could explain differences in plant EG and GS. Conclusions: Salts accumulated in the vadose zone at both sites so usable water was confined to the saturated capillary fringe above the aquifer. Existence of a saline aquifer imposes several types of constraints on phreatophyte EG, which need to be considered in models of plant water uptake. The heterogeneous nature of saltcedar EG over river terraces introduces potential errors into estimates of ET by wide-area methods. © 2013 Springer Science+Business Media Dordrecht.
• Gómez-Sapiens, M. M., Tang, D., Glenn, E. P., Lomelí, M. A., Ramírez-Hernández, J., & Pitt, J. (2013). Modeling water management scenarios for the Cienega de Santa Clara, an anthropogenic coastal desert wetland system, based on inflow volumes and salinities. Ecological Engineering, 59, 30-40.
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  Abstract: The Cienega de Santa Clara in the Colorado River Delta, Mexico is a self-designed wetland system fed since 1977 by brackish groundwater diverted from the U.S. to Mexico. The vegetated upper portion of the Cienega provides habitat for endangered Yuma-Clappers rails and other marsh birds and fulfills other ecological functions. Outflow water pools in the Santa Clara Slough south of the Cienega and provides habitat for migratory shorebirds. Conditions in the Cienega and Santa Clara Slough could be altered by operation of the Yuma Desalting Plant (YDP), which will divert water from the Cienega and replace it with brine water resulting from the desalting process. Our objective was to integrate water budget components into models predicting the extent of the dominant vegetation (southern cattail, Typha domingensis Pers.) in the marsh and the area of the outflow pool below the marsh in response to different operating scenarios for the YDP. The models are intended to serve as tools for resource managers charged with maintaining this wetland complex. Unlike many wetland water budget models, this one explicitly takes into account salinity as a factor in the water budget. We modeled inflow rates ranging from 1 to 6m3s-1 and inflow salinities ranging from 0 to 6gL-1 Total Dissolved Solids. The model indicates that if the inflow rate is reduced below the current 4-5m3s-1 the vegetated area of the Cienega would decrease in proportion, as would the area of the outflow pool in the Santa Clara Slough. Increases in salinity will also reduce the vegetated area due to the low salt tolerance of T. domingensis. In winter about 90% of inflow water exits the Cienega into the Santa Clara Slough due to low evapotranspiration, and on an annual basis 70% of inflows exit into the Santa Clara Slough. These flushing flows maintain the salt balance in the Cienega. The Santa Clara Slough is periodically flushed by spring tides, making this a sustainable, open wetland system in its present state. © 2013 Elsevier B.V.
• Hinojosa-Huerta, O., Nagler, P. L., Carrillo-Guererro, Y. K., & Glenn, E. P. (2013). Effects of drought on birds and riparian vegetation in the Colorado River Delta, Mexico. Ecological Engineering, 51, 275-281.
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  Abstract: The riparian corridor in the delta of the Colorado River in Mexico supports internationally important bird habitat. The vegetation is maintained by surface flows from the U.S. and Mexico and by a high, non-saline aquifer into which the dominant phreatophytic shrubs and trees are rooted. We studied the effects of a regional drought on riparian vegetation and avian abundance and diversity from 2002 to 2007, during which time surface flows were markedly reduced compared to the period from 1995 to 2002. Reduced surface flows led to a reduction in native tree cover but an increase in shrub cover, mostly due to an increase in Tamarix spp., an introduced halophytic shrub, and a reduction in Populus fremontii and Salix gooddingii trees. However, overall vegetation cover was unchanged at about 70%. Overall bird density and diversity were also unchanged, but riparian-obligate species tended to decrease in abundance, and generalist species increased. Although reduction in surface flows reduced habitat value and negatively impacted riparian-obligate bird species, portions of the riparian zone exhibited resilience. Surface flows are required to reduce soil salt levels and germinate new cohorts of native trees, but the main source of water supporting this ecosystem is the aquifer, derived from underflows from irrigated fields in the U.S. and Mexico. The long-term prospects for delta riparian habitats are uncertain due to expected reduced flows of river water from climate change, and land use practices that will reduce underflows to the riparian aquifer and increase salinity levels. Active restoration programs would be needed if these habitats are to be preserved for the future. © 2012 Elsevier B.V.
• Hinojosa-Huerta, O., Nagler, P. L., Carrillo-Guererro, Y. K., & Glenn, E. P. (2013). Reprint of: Effects of drought on birds and riparian vegetation in the Colorado River Delta, Mexico. Ecological Engineering, 59, 104-110.
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  Abstract: The riparian corridor in the delta of the Colorado River in Mexico supports internationally important bird habitat. The vegetation is maintained by surface flows from the U.S. and Mexico and by a high, non-saline aquifer into which the dominant phreatophytic shrubs and trees are rooted. We studied the effects of a regional drought on riparian vegetation and avian abundance and diversity from 2002 to 2007, during which time surface flows were markedly reduced compared to the period from 1995 to 2002. Reduced surface flows led to a reduction in native tree cover but an increase in shrub cover, mostly due to an increase in saltcedar (Tamarix spp.), an introduced halophytic shrub, and a reduction in cottonwood (Populus fremontii) and willow (Salix gooddingii) trees. However, overall vegetation cover was unchanged at about 70%. Overall bird density and diversity were also unchanged, but riparian-obligate species tended to decrease in abundance, and generalist species increased. Although reduction in surface flows reduced habitat value and negatively impacted riparian-obligate bird species, portions of the riparian zone exhibited resilience. Surface flows are required to reduce soil salt levels and germinate new cohorts of native trees, but the main source of water supporting this ecosystem is the aquifer, derived from underflows from irrigated fields in the U.S. and Mexico. The long-term prospects for delta riparian habitats are uncertain due to expected reduced flows of river water from climate change, and land use practices that will reduce underflows to the riparian aquifer and increase salinity levels. Active restoration programs would be needed if these habitats are to be preserved for the future. El corredor ripario en el delta del río Colorado en México contiene hábitat para aves de importancia internacional. La vegetación se mantiene con flujos superficiales de E.U. y México y por un acuífero somero de baja salinidad al cual llegan las raíces de los arbustos y árboles freatofíticos. Estudiamos los efectos de una sequía regional sobre la vegetación riparia y la abundancia y diversidad de aves entre el 2002 y 2007, periodo en el que los flujos superficiales se redujeron drásticamente, en comparación con el periodo entre 1995-2002. La reducción de flujos superficiales causó la reducción en cobertura de árboles nativos y un incremento en la cobertura de arbustos, principalmente por el aumento de Tamarix spp., un arbusto halófito introducido, y por la pérdida de Populus fremontii y Salix gooddingii. Sin embargo, la cobertura vegetal se mantuvo sin cambio, en cerca de 70%. La densidad y diversidad de aves también se mantuvo, pero la abundancia de especies riparias descendió, mientras que las especies generalistas aumentaron. Aunque la reducción en flujos superficiales redujo el valor de hábitat y afectó negativamente a las aves riparias, algunas porciones de la zona exhibieron resiliencia. Los flujos superficiales se requieren para reducir la salinidad en el suelo y para la germinación de nuevos cohortes de árboles nativos, pero la principal fuente de agua para este ecosistema es el acuífero, derivado de los flujos subterráneos que provienen de la irrigación agrícola en E.U. y México. La expectativa para los hábitats riparios en el delta es incierta debido a que se espera una reducción en los flujos superficiales a causa del cambio climático, y por las prácticas que reducirán los flujos subterráneos y aumentarán la salinidad. Para poder preservar estos hábitats hacia el futuro se requiere la implementación de programas de restauración activa. © 2013 Elsevier B.V.
• Nagler, P. L., Glenn, E. P., Morino, K., & Hultine, K. R. (2013). Phreatophytes under stress: Review of studies on transpiration and stomatal conductance of Tamarix across a Western US floodplain. Acta Horticulturae, 991, 61-66.
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  Abstract: Transpiration (EL) and stomatal conductance (GS) were measured with stem heat-balance and Granier sap flux sensors on the dominant phreatophyte, saltcedar (Tamarix spp.), growing at six sites on a floodplain on the Lower Colorado River, US. Plant-specific leaf area index (LAPS) of shrubs was measured by leaf harvesting and Licor 2000 Plant Canopy Analyzer, and fractional cover (fc) was estimated by aerial imagery. Ground-area transpiration (EG) was calculated as EL × LAPS × fc. The sites presented environmental gradients with respect to distance from the river (0.2-1.5 km), depth to groundwater (2.4-3.5 m), groundwater salinity [1.9-24.0 g L-1 Total Dissolved Solids (TDS)] and soil texture (ranging from sand to clayey silts). EL aried from 1-3 mm m-1 leaf d-1 across sites, while LAPS ranged more narrowly, from 2-4, and fc varied from 0.5-0.95. Due to differences in EL, LAPS and fc, EG ranged from 1.2-9.5 mm d-1, nearly a 10-fold range. Only one site had EG characteristic of unstressed condition. We concluded that saltcedar is capable of high EG rates, but is also a stress adapted species, with E G highly variable over nonflooding riparian zones typical of regulated rivers. Salinity of the aquifer and vadose zone were identified as key constraints on saltcedar EG. Mean EG over the floodplain was only 40% of potential ET, contrary to earlier assumptions that saltcedar is invariably a high-water use plant. © ISHS 2013.
• Nagler, P. L., Glenn, E. P., Nguyen, U., Scott, R. L., & Doody, T. (2013). Estimating riparian and agricultural actual evapotranspiration by reference evapotranspiration and MODIS enhanced vegetation index. Remote Sensing, 5(8), 3849-3871.
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  Abstract: Dryland river basins frequently support both irrigated agriculture and riparian vegetation and remote sensing methods are needed to monitor water use by both crops and natural vegetation in irrigation districts. We developed an algorithm for estimating actual evapotranspiration (ETa) based on the Enhanced Vegetation Index (EVI) from the Moderate Resolution Imaging Spectrometer (MODIS) sensor on the EOS-1 Terra satellite and locally-derived measurements of reference crop ET (ETo). The algorithm was calibrated with five years of ETa data from three eddy covariance flux towers set in riparian plant associations on the upper San Pedro River, Arizona, supplemented with ETa data for alfalfa and cotton from the literature. The algorithm was based on an equation of the form ETa = ETo [a(1 - e-bEVI) - c], where the term (1 - e-bEVI) is derived from the Beer-Lambert Law to express light absorption by a canopy, with EVI replacing leaf area index as an estimate of the density of light-absorbing units. The resulting algorithm capably predicted ETa across riparian plants and crops (r2 = 0.73). It was then tested against water balance data for five irrigation districts and flux tower data for two riparian zones for which season-long or multi-year ETa data were available. Predictions were within 10% of measured results in each case, with a non-significant (P = 0.89) difference between mean measured and modeled ETa of 5.4% over all validation sites. Validation and calibration data sets were combined to present a final predictive equation for application across crops and riparian plant associations for monitoring individual irrigation districts or for conducting global water use assessments of mixed agricultural and riparian biomes. © 2013 by the authors.
• Nagler, P., & Glenn, E. (2013). Tamarix and Diorhabda Leaf Beetle Interactions: Implications for Tamarix Water Use and Riparian Habitat. Journal of the American Water Resources Association, 49(3), 534-548.
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  Abstract: Tamarix leaf beetles (Diorhabda carinulata) have been widely released on western United States rivers to control introduced shrubs in the genus Tamarix, with the goals of saving water through removal of an assumed high water-use plant, and of improving habitat value by removing a competitor of native riparian trees. We review recent studies addressing three questions: (1) to what extent are Tamarix weakened or killed by recurrent cycles of defoliation; (2) can significant water salvage be expected from defoliation; and (3) what are the effects of defoliation on riparian ecology, particularly on avian habit? Defoliation has been patchy at many sites, and shrubs at some sites recover each year even after multiple years of defoliation. Tamarix evapotranspiration (ET) is much lower than originally assumed in estimates of potential water savings, and are the same or lower than possible replacement plants. There is concern that the endangered southwestern willow flycatcher (Empidonax trailli extimus) will be negatively affected by defoliation because the birds build nests early in the season when Tamarix is still green, but are still on their nests during the period of summer defoliation. Affected river systems will require continued monitoring and development of adaptive management practices to maintain or enhance riparian habitat values. Multiplatform remote sensing methods are playing an essential role in monitoring defoliation and rates of ET on affected river systems. © 2013 American Water Resources Association.
• Borden, A. K., Brusseau, M. L., Carroll, K. C., McMillan, A., Akyol, N. H., Berkompas, J., Miao, Z., Jordan, F., Tick, G., Waugh, W. J., & Glenn, E. P. (2012). Ethanol addition for enhancing denitrification at the uranium mill tailing site in Monument Valley, AZ. Water, Air, and Soil Pollution, 223(2), 755-763.
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  Abstract: Past mining and processing of uranium ore at a former uranium mining site near Monument Valley, AZ has resulted in nitrate contamination of groundwater. The objective of this study was to investigate the potential of ethanol addition for enhancing the reduction of nitrate in groundwater. The results of two pilot-scale field tests showed that the concentration of nitrate decreased, while the concentration of nitrous oxide (a product of denitrification) increased. In addition, changes in aqueous concentrations of sulfate, iron, and manganese indicated that the ethanol amendment caused a change in prevailing redox conditions. The results of compound-specific stable isotope analysis for nitrate-nitrogen indicated that the nitrate concentration reductions were biologically mediated. Denitrification rate coefficients estimated for the pilot tests were approximately 50 times larger than resident-condition (non-enhanced) values obtained from prior characterization studies conducted at the site. The nitrate concentrations in the injection zone have remained at levels three orders of magnitude below the initial values for many months, indicating that the ethanol amendments had a long-term impact on the local subsurface environment. © Springer Science+Business Media B.V. 2011.
• Glenn, E. P., Morino, K., Nagler, P. L., Murray, R. S., Pearlstein, S., & Hultine, K. R. (2012). Roles of saltcedar (Tamarix spp.) and capillary rise in salinizing a non-flooding terrace on a flow-regulated desert river. Journal of Arid Environments, 79, 56-65.
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  Abstract: Tamarix spp. (saltcedar) secretes salts and has been considered to be a major factor contributing to the salinization of river terraces in western US riparian zones. However, salinization can also occur from the capillary rise of salts from the aquifer into the vadose zone. We investigated the roles of saltcedar and physical factors in salinizing the soil profile of a non-flooding terrace at sites on the Cibola National Wildlife Refuge on the Lower Colorado River, USA. We placed salt traps under and between saltcedar shrubs and estimated the annual deposition rate of salts from saltcedar. These were then compared to the quantities and distribution on of salts in the soil profile. Dense stands of saltcedar deposited 0.159kgm -2yr -1 of salts to the soil surface. If this rate was constant since seasonal flooding ceased in 1938 and all of the salts were retained in the soil profile, they could account for 11.4kgm -2 of salt, about 30% of total salts in the profile today. Eliminating saltcedar would not necessarily reduce salts, because vegetation reduces the upward migration of salts in bulk flow from the aquifer. The densest saltcedar stand had the lowest salt levels in the vadose zone in this study. © 2011 Elsevier Ltd.
• Glenn, E. P., Nelson, S. G., Ambrose, B., Martinez, R., Soliz, D., Pabendinskas, V., & Hultine, K. (2012). Comparison of salinity tolerance of three Atriplex spp. in well-watered and drying soils. Environmental and Experimental Botany, 83, 62-72.
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  Abstract: Members of the Chenopodiaceae are well adapted to both salt and drought stress and can serve as model species to understand the mechanisms of tolerance in plants. We grew Atriplex hortensis (ATHO), A. canescens (ATCA), and A. lentiformis (ATLE) along a NaCL salinity gradient under non-water-limited conditions and in drying soils in greenhouse experiments. The species differed in photosynthetic carbon fixation pathway, capacity for sodium uptake, and habitat preferences. Under non-water-limited conditions, ATLE (C4) maintained high growth rates up to 30gL -1 NaCl. ATHO (C3) had lower growth than ATLE at high salinities, while ATCA (C4) grew more slowly than either ATLE or ATHO and showed no net growth above 20gL -1 NaCl. ATHO and ATLE accumulated twice as much sodium in their shoots as ATCA, but all three species had increasing sodium levels at higher salinities. Potassium, magnesium and calcium levels were relatively constant over the salinity gradient. All three species showed marked accumulation of chloride across the salinity gradient, whereas nitrate, phosphorous and sulfate decreased with salinity. The effect of drought was simulated by growing plants in sealed pots with an initial charge of water plus NaCl, and allowing them to grow to the end point at which they no longer were able to extract water from the soil solution. Drought and salinity were not additive stress factors for Atriplex spp. in this experiment. NaCl increased their ability to extract water from the soil solution compared to fresh water controls. ATLE showed increased shoot dry matter production and increased water use efficiency (WUE) as initial salinity levels increased from 0 to 30gL -1 NaCl, whereas dry matter production and WUE peaked at 5gL -1 for ATHO and ATCA. Final soil moisture salinities tolerated by species were 85gL -1, 55gL -1 and 160gL -1 NaCl for ATHO, ATCA and ATLE, respectively. C4 photosynthesis and sodium accumulation in shoots were associated with high drought and salt tolerance. © 2012 Elsevier B.V.
• Mexicano, L., Nagler, P. L., Zamora-Arrroyo, F., & Glenn, E. P. (2012). Vegetation dynamics in response to water inflow rates and fire in a brackish Typha domingensis Pers. marsh in the delta of the Colorado River, Mexico. Ecological Engineering, 59, 167-175.
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  Abstract: The Cienega de Santa Clara is a 5600. ha, anthropogenic wetland in the delta of the Colorado River in Mexico. It is the inadvertent creation of the disposal of brackish agricultural waste water from the U.S. into the intertidal zone of the river delta in Mexico, but has become an internationally important wetland for resident and migratory water birds. We used high resolution Quickbird and WorldView-2 images to produce seasonal vegetation maps of the Cienega before, during and after a test run of the Yuma Desalting Plant, which will remove water from the inflow stream and replace it with brine. We also used moderate resolution, 16-day composite NDVI imagery from the Moderate Resolution Imaging Spectrometer (MODIS) sensors on the Terra satellite to determine the main factors controlling green vegetation density over the years 2000-2011. The marsh is dominated by Typha domingensis Pers. with Phragmites australis (Cav.) Trin. Ex Steud. as a sub-dominant species in shallower marsh areas. The most important factor controlling vegetation density was fire. Spring fires in 2006 and 2011 were followed by much more rapid green-up of T. domingensis in late spring and 30% higher peak summer NDVI values compared to non-fire years (P
• Nagler, P. L., Brown, T., Hultine, K. R., Riper, C. v., Bean, D. W., Dennison, P. E., Murray, R. S., & Glenn, E. P. (2012). Regional scale impacts of Tamarix leaf beetles (Diorhabda carinulata) on the water availability of western U.S. rivers as determined by multi-scale remote sensing methods. Remote Sensing of Environment, 118, 227-240.
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  Abstract: Tamarix leaf beetles (Diorhabda carinulata) have been widely released on western U.S. rivers to control introduced shrubs in the genus Tamarix. Part of the motivation to control Tamarix is to salvage water for human use. Information is needed on the impact of beetles on Tamarix seasonal leaf production and subsequent water use over wide areas and multiple cycles of annual defoliation. Here we combine ground data with high resolution phenocam imagery and moderate resolution (Landsat) and coarser resolution (MODIS) satellite imagery to test the effects of beetles on Tamarix evapotranspiration (ET) and leaf phenology at sites on six western rivers. Satellite imagery covered the period 2000 to 2010 which encompassed years before and after beetle release at each study site. Phenocam images showed that beetles reduced green leaf cover of individual canopies by about 30% during a 6-8week period in summer, but plants produced new leaves after beetles became dormant in August, and over three years no net reduction in peak summer leaf production was noted. ET was estimated by vegetation index methods, and both Landsat and MODIS analyses showed that beetles reduced ET markedly in the first year of defoliation, but ET recovered in subsequent years. Over all six sites, ET decreased by 14% to 15% by Landsat and MODIS estimates, respectively. However, results were variable among sites, ranging from no apparent effect on ET to substantial reduction in ET. Baseline ET rates before defoliation were low, 394mmyr -1 by Landsat and 314mmyr -1 by MODIS estimates (20-25% of potential ET), further constraining the amount of water that could be salvaged. Beetle-Tamarix interactions are in their early stage of development on this continent and it is too soon to predict the eventual extent to which Tamarix populations will be reduced. The utility of remote sensing methods for monitoring defoliation was constrained by the small area covered by each phenocam image, the low temporal resolution of Landsat, and the low spatial resolution of MODIS imagery. Even combined image sets did not adequately reveal the details of the defoliation process, and remote sensing data should be combined with ground observations to develop operational monitoring protocols. © 2011 .
• Nagler, P. L., Glenn, E. P., & Morino, K. (2012). Comparison of sap flux, moisture flux tower and MODIS Enhanced Vegetation Index methods for estimating riparian evapotranspiration. IAHS-AISH Publication, 352, 410-413.
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  Abstract: Riparian evapotranspiration (ET) was measured on a salt cedar (Tamarix spp.) dominated river terrace on the Lower Colorado River from 2007 to 2009 using tissue-heat-balance sap flux sensors at six sites representing very dense, medium dense, and sparse stands of plants. Salt cedar ET varied markedly across sites, and sap flux sensors showed that plants were subject to various degrees of stress, detected as mid-day depression of transpiration and stomatal conductance. Sap flux results were scaled from the leaf level of measurement to the stand level by measuring plant-specific leaf area index and fractional ground cover at each site. Results were compared to Bowen ratio moisture tower data available for three of the sites. Sap flux sensors and flux tower results ranked the sites the same and had similar estimates of ET. A regression equation, relating measured ET of salt cedar and other riparian plants and crops on the Lower Colorado River to the Enhanced Vegetation Index from the MODIS sensor on the Terra satellite and reference crop ET measured at meteorological stations, was able to predict actual ET with an accuracy or uncertainty of about 20%, despite between-site differences for salt cedar. Peak summer salt cedar ET averaged about 6 mm d-1 across sites and methods of measurement. Copyright © 2012 IAHS Press.
• Pearlstein, S. L., Felger, R. S., Glenn, E. P., Harrington, J., Al-Ghanem, K., & Nelson, S. G. (2012). Nipa (Distichlis palmeri): A perennial grain crop for saltwater irrigation. Journal of Arid Environments, 82, 60-70.
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  Abstract: The perennial saltgrass nipa (Distichlis palmeri, Poaceae) is endemic to northern Gulf of California tidal marshes flooded with hypersaline (38-42gL -1) seawater. Nipa was a wild harvest staple of the Cocopah people of the Río Colorado delta. We investigated the physiology, anatomy, chromosome number, and agronomic potential of nipa as a global food crop. Nipa seeds had 60-93% germination on salinities ranging from 0 to 30gL -1. Relative Growth Rates (RGR) on both flooded and aerobic conditions remained above 4% d -1 up to 30gL -1, about half the RGR on freshwater. Nipa grain (caryopses) had 7-8% protein, 8% sugar and 79% total digestible carbohydrates (mostly starch) and only 2% ash and 8% fiber, equal to conventional grains in apparent nutritional value. Shoots were low in ash and sodium, and compared favorably to alfalfa forage in protein, digestible carbohydrates and energy contents. Mature female stands in the Colorado River delta produced an estimated 1.25tha -1 of grain, but over two years in the greenhouse only partial flowering was observed. Nevertheless, D. palmeri appears to be worth developing as a perennial grain and forage crop, especially for salinized, flooded soils. © 2012 Elsevier Ltd.
• Tillman, F. D., Callegary, J. B., Nagler, P. L., & Glenn, E. P. (2012). A simple method for estimating basin-scale groundwater discharge by vegetation in the basin and range province of Arizona using remote sensing information and geographic information systems. Journal of Arid Environments, 82, 44-52.
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  Abstract: Groundwater is a vital water resource in the arid to semi-arid southwestern United States. Accurate accounting of inflows to and outflows from the groundwater system is necessary to effectively manage this shared resource, including the important outflow component of groundwater discharge by vegetation. A simple method for estimating basin-scale groundwater discharge by vegetation is presented that uses remote sensing data from satellites, geographic information systems (GIS) land cover and stream location information, and a regression equation developed within the Southern Arizona study area relating the Enhanced Vegetation Index from the MODIS sensors on the Terra satellite to measured evapotranspiration. Results computed for 16-day composited satellite passes over the study area during the 2000 through 2007 time period demonstrate a sinusoidal pattern of annual groundwater discharge by vegetation with median values ranging from around 0.3 mm per day in the cooler winter months to around 1.5 mm per day during summer. Maximum estimated annual volume of groundwater discharge by vegetation was between 1.4 and 1.9 billion m 3 per year with an annual average of 1.6 billion m 3. A simplified accounting of the contribution of precipitation to vegetation greenness was developed whereby monthly precipitation data were subtracted from computed vegetation discharge values, resulting in estimates of minimum groundwater discharge by vegetation. Basin-scale estimates of minimum and maximum groundwater discharge by vegetation produced by this simple method are useful bounding values for groundwater budgets and groundwater flow models, and the method may be applicable to other areas with similar vegetation types. © 2012.
• Doody, T. M., Nagler, P. L., Glenn, E. P., Moore, G. W., Morino, K., Hultine, K. R., & Benyon, R. G. (2011). Potential for water salvage by removal of non-native woody vegetation from dryland river systems. Hydrological Processes, 25(26), 4117-4131.
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  Abstract: Globally, expansion of non-native woody vegetation across floodplains has raised concern of increased evapotranspiration (ET) water loss with consequent reduced river flows and groundwater supplies. Water salvage programs, established to meet water supply demands by removing introduced species, show little documented evidence of program effectiveness. We use two case studies in the USA and Australia to illustrate factors that contribute to water salvage feasibility for a given ecological setting. In the USA, saltcedar (Tamarix spp.) has become widespread on western rivers, with water salvage programs attempted over a 50-year period. Some studies document riparian transpiration or ET reduction after saltcedar removal, but detectable increases in river base flow are not conclusively shown. Furthermore, measurements of riparian vegetation ET in natural settings show saltcedar ET overlaps the range measured for native riparian species, thereby constraining the possibility of water salvage by replacing saltcedar with native vegetation. In Australia, introduced willows (Salix spp.) have become widespread in riparian systems in the Murray-Darling Basin. Although large-scale removal projects have been undertaken, no attempts have been made to quantify increases in base flows. Recent studies of ET indicate that willows growing in permanently inundated stream beds have high transpiration rates, indicating water savings could be achieved from removal. In contrast, native Eucalyptus trees and willows growing on stream banks show similar ET rates with no net water salvage from replacing willows with native trees. We conclude that water salvage feasibility is highly dependent on the ecohydrological setting in which the non-native trees occur. We provide an overview of conditions favorable to water salvage. Copyright © 2011 John Wiley & Sons, Ltd.
• Glenn, E. P., Doody, T. M., Guerschman, J. P., Huete, A. R., King, E. A., Mcvicar, T. R., I., A., G., T., Yebra, M., & Zhang, Y. (2011). Actual evapotranspiration estimation by ground and remote sensing methods: the Australian experience. Hydrological Processes, 25(26), 4103-4116.
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  Abstract: On average, Australia is a dry continent with many competing uses for water. Hence, there is an urgent need to know actual evapotranspiration (ET a) patterns across wide areas of agricultural and natural ecosystems, as opposed to just point measurements of ET a. The Australian Government has tasked the science agencies with operationally developing monthly and annual estimates of ET a and other hydrological variables, and with forecasting water availability over periods of days to decades, as part of its national water assessment programme. To meet these needs, Australian researchers have become leaders in developing large-area methods for estimating ET a at regional and continental scales. Ground methods include meteorological models, eddy covariance towers, sap flow sensors and catchment water balance models. Remote sensing methods use thermal infrared, mid infrared and/or vegetation indices usually combined with meteorological data to estimate ET a. Ground and remote sensing ET a estimates are assimilated into the Australian Water Resource Assessment, which issues annual estimates of the state of the continental water balance for policy and planning purposes. The best ET a models are estimated to have an error or uncertainty of 10% to 20% in Australia. Developments in Australian ET a research over the past 20years are reviewed, and sources of error and uncertainty in current methods and models are discussed. Copyright © 2011 John Wiley & Sons, Ltd.
• Glenn, E. P., M., C., Hunsaker, D. J., & Nagler, P. L. (2011). Vegetation index-based crop coefficients to estimate evapotranspiration by remote sensing in agricultural and natural ecosystems. Hydrological Processes, 25(26), 4050-4062.
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  Abstract: Crop coefficients were developed to determine crop water needs based on the evapotranspiration (ET) of a reference crop under a given set of meteorological conditions. Starting in the 1980s, crop coefficients developed through lysimeter studies or set by expert opinion began to be supplemented by remotely sensed vegetation indices (VI) that measured the actual status of the crop on a field-by-field basis. VIs measure the density of green foliage based on the reflectance of visible and near infrared (NIR) light from the canopy, and are highly correlated with plant physiological processes that depend on light absorption by a canopy such as ET and photosynthesis. Reflectance-based crop coefficients have now been developed for numerous individual crops, including corn, wheat, alfalfa, cotton, potato, sugar beet, vegetables, grapes and orchard crops. Other research has shown that VIs can be used to predict ET over fields of mixed crops, allowing them to be used to monitor ET over entire irrigation districts. VI-based crop coefficients can help reduce agricultural water use by matching irrigation rates to the actual water needs of a crop as it grows instead of to a modeled crop growing under optimal conditions. Recently, the concept has been applied to natural ecosystems at the local, regional and continental scales of measurement, using time-series satellite data from the MODIS sensors on the Terra satellite. VIs or other visible-NIR band algorithms are combined with meteorological data to predict ET in numerous biome types, from deserts, to arctic tundra, to tropical rainforests. These methods often closely match ET measured on the ground at the global FluxNet array of eddy covariance moisture and carbon flux towers. The primary advantage of VI methods for estimating ET is that transpiration is closely related to radiation absorbed by the plant canopy, which is closely related to VIs. The primary disadvantage is that they cannot capture stress effects or soil evaporation. Copyright © 2011 John Wiley & Sons, Ltd.
• Nagler, P. L., Glenn, E. P., Jarnevich, C. S., & Shafroth, P. B. (2011). Distribution and abundance of Saltcedar and Russian Olive in the Western United States. Critical Reviews in Plant Sciences, 30(6), 508-523.
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  Abstract: Over the past century, two introduced Eurasian trees, saltcedar (Tamarix spp.) and Russian olive (Elaeagnus angustifolia) have become wide spread on western United States of American (U.S.) rivers. This paper reviews the literature on the following five key areas related to their distribution and abundance in the western United States: (1) the history of introduction, planting, and spread of saltcedar and Russian olive; (2) their current distribution; (3) their current abundance; (4) factors controlling their current distribution and abundance; and (5) models that have been developed to predict their future distribution and abundance. Saltcedar and Russian olive are now the third and fourth most frequently occurring woody riparian plants and the second and fifth most abundant species (out of 42 native and non-native species) along rivers in the western United States. Currently there is not a precise estimate of the areas that these species occupy in the entire West. Climatic variables are important determinants of their distribution and abundance. For example, saltcedar is limited by its sensitivity to hard freezes, whereas Russian olive appears to have a chilling requirement for bud break and seed germination, and can presumably survive colder winter temperatures. Either species can be dominant, co-dominant or sub-dominant relative to native species on a given river system. A number of environmental factors such as water availability, soil salinity, degree of stream flow regulation, and fire frequency can influence the abundance of these species relative to native species. Numerous studies suggest that both species have spread on western rivers primarily through a replacement process, hereby stress-tolerant species have moved into expanded niches that are no longer suitable for mesic native pioneer species. Better maps of current distribution and rigorous monitoring of distributional changes though time can help to resolve differences in predictions of potential future spread. An adequate understanding does not yet exist of what fraction of western riparian zones is resistant to dominance by either of these species, what fraction is at risk and could benefit from intervention, and what fraction has been altered to the point that saltcedar or Russian olive are most likely to thrive.
• Senay, G. B., Leake, S., Nagler, P. L., Artan, G., Dickinson, J., Cordova, J. T., & Glenn, E. P. (2011). Estimating basin scale evapotranspiration (ET) by water balance and remote sensing methods. Hydrological Processes, 25(26), 4037-4049.
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  Abstract: Evapotranspiration (ET) is an important hydrological process that can be studied and estimated at multiple spatial scales ranging from a leaf to a river basin. We present a review of methods in estimating basin scale ET and its applications in understanding basin water balance dynamics. The review focuses on two aspects of ET: (i) how the basin scale water balance approach is used to estimate ET; and (ii) how 'direct' measurement and modelling approaches are used to estimate basin scale ET. Obviously, the basin water balance-based ET requires the availability of good precipitation and discharge data to calculate ET as a residual on longer time scales (annual) where net storage changes are assumed to be negligible. ET estimated from such a basin water balance principle is generally used for validating the performance of ET models. On the other hand, many of the direct estimation methods involve the use of remotely sensed data to estimate spatially explicit ET and use basin-wide averaging to estimate basin scale ET. The direct methods can be grouped into soil moisture balance modelling, satellite-based vegetation index methods, and methods based on satellite land surface temperature measurements that convert potential ET into actual ET using a proportionality relationship. The review also includes the use of complementary ET estimation principles for large area applications. The review identifies the need to compare and evaluate the different ET approaches using standard data sets in basins covering different hydro-climatic regions of the world. Copyright © 2011 John Wiley & Sons, Ltd.
• Soliz, D., Glenn, E. P., Seaman, R., Yoklic, M., Nelson, S. G., & Brown, P. (2011). Water consumption, irrigation efficiency and nutritional value of Atriplex lentiformis grown on reverse osmosis brine in a desert irrigation district. Agriculture, Ecosystems and Environment, 140(3-4), 473-483.
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  Abstract: Arid regions in southwestern U.S. are faced with increased water shortages with the possibility of compromised water quality. The use of impaired water resources, including saline water, for agriculture is a possibility. The halophyte forage shrub Atriplex lentiformis (quailbush) was irrigated over three growing seasons with brine (2.6-3.2gL-1 total dissolved solids) from a reverse-osmosis water treatment plant in an agricultural district in Marana, Arizona, in the Sonoran Desert, U.S. The goal was to determine if a halophyte crop could be grown productively on saline irrigation water in a way that maximized yield yet minimized excess deep percolation of salt past the root zone. Our hypotheses for this project were: (1) A. lentiformis could consume water at or above the potential evapotranspiration rate (ETo) measured at an on-site meteorological stations; (2) need for a leaching fraction could be minimized due to the high salt tolerance of the crop; and (3) water could be presented on a constant schedule typical of the delivery from a desalination plant, with excess water presented in winter utilized in summer via the deep rooting systems of A. lentiformis. Three irrigation treatments were tested based on the potential evapotranspiration rate (ETo): (1) plots irrigated at ETo adjusted daily via an on-site micrometeorology station; (2) plots irrigated at 1.5 ETo adjusted daily; (3) plots irrigated at a constant rate throughout the year based on the mean of annual ETo. The plants produced 15-22tonsha-1year-1 of biomass and could be irrigated at the rate of ETo, ca. 2myear-1 at this location. Drainage volumes ranged from no drainage in Treatment 1 to 12-14% of applied water in Treatments 2 and 3. It is concluded that irrigation of halophyte forage crops provide a viable strategy for extending water supplies and disposing of saline water in arid-zone irrigation districts. © 2011 Elsevier B.V.
• Glenn, E. P., Nagler, P. L., & Huete, A. R. (2010). Vegetation Index Methods for Estimating Evapotranspiration by Remote Sensing. Surveys in Geophysics, 31(6), 531-555.
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  Abstract: Evapotranspiration (ET) is the largest term after precipitation in terrestrial water budgets. Accurate estimates of ET are needed for numerous agricultural and natural resource management tasks and to project changes in hydrological cycles due to potential climate change. We explore recent methods that combine vegetation indices (VI) from satellites with ground measurements of actual ET (ETa) and meteorological data to project ETa over a wide range of biome types and scales of measurement, from local to global estimates. The majority of these use time-series imagery from the Moderate Resolution Imaging Spectrometer on the Terra satellite to project ET over seasons and years. The review explores the theoretical basis for the methods, the types of ancillary data needed, and their accuracy and limitations. Coefficients of determination between modeled ETa and measured ETa are in the range of 0.45-0.95, and root mean square errors are in the range of 10-30% of mean ETa values across biomes, similar to methods that use thermal infrared bands to estimate ETa and within the range of accuracy of the ground measurements by which they are calibrated or validated. The advent of frequent-return satellites such as Terra and planed replacement platforms, and the increasing number of moisture and carbon flux tower sites over the globe, have made these methods feasible. Examples of operational algorithms for ET in agricultural and natural ecosystems are presented. The goal of the review is to enable potential end-users from different disciplines to adapt these methods to new applications that require spatially-distributed ET estimates. © 2010 Springer Science+Business Media B.V.
• Hartwell, S., Morino, K., Nagler, P. L., & Glenn, E. P. (2010). On the irrigation requirements of cottonwood (Populus fremontii and Populus deltoides var. wislizenii) and willow (Salix gooddingii) grown in a desert environment. Journal of Arid Environments, 74(6), 667-674.
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  Abstract: Native tree plots have been established in river irrigation districts in the western U.S. to provide habitat for threatened and endangered birds. Information is needed on the effective irrigation requirements of the target species. Cottonwood (Populus spp.) and willow (Salix gooddingii) trees were grown for seven years in an outdoor plot in a desert environment in Tucson, Arizona. Plants were allowed to achieve a nearly complete canopy cover over the first four years, then were subjected to three daily summer irrigation schedules of 6.20 mm d-1; 8.26 mm d-1 and 15.7 mm d-1. The lowest irrigation rate was sufficient to maintain growth and high leaf area index for cottonwoods over three years, while willows suffered considerable die-back on this rate in years six and seven. These irrigation rates were applied April 15-September 15, but only 0.88 mm d-1 was applied during the dormant period of the year. Expressed as a fraction of reference crop evapotranspiration (ETo), recommended annual water applications plus precipitation (and including some deep drainage) were 0.83 ETo for cottonwood and 1.01 ETo for willow. Current practices tend to over-irrigate restoration plots, and this study can provide guidelines for more efficient water use. © 2010 Elsevier Ltd.
• Huckelbridge, K. H., Stacey, M. T., Glenn, E. P., & Dracup, J. A. (2010). An integrated model for evaluating hydrology, hydrodynamics, salinity and vegetation cover in a coastal desert wetland. Ecological Engineering, 36(7), 850-861.
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  Abstract: An integrated model describing hydrology, hydrodynamics, salt dynamics and vegetation was developed to predict the evolution of the Ciénega de Santa Clara, a non-tidal, anthropogenic wetland located in the Colorado River Delta. The Ciénega, an important part of the Delta ecosystem, is supported by saline groundwater from the U.S. that is sent to Mexico to control salinity in the U.S. The future of this water source is uncertain, and thus, the model was developed to predict how the Ciénega would respond to changes in the quantity and salinity of its inflow. Over the calibration period, 1993-2007, modeled results of wetland surface area, the fraction of the wetland covered in vegetation and salinity concentrations compare well to actual data. The model shows that between 1993 and 2007 evapotranspiration rates range from 0 to 8 mm/day, wetland surface area increases 44% from 4500 to 6500 ha, the fraction of the wetland covered in vegetation decreases slightly from 0.92 to 0.88, and the mean salinity concentration in the wetland increases from 3100 to 6700 ppm. The model was used to run nine hypothetical scenarios, representing the range of inflow quantity and salinity to the Ciénega that could occur if the source of the inflow is altered, including the possible re-opening of the Yuma Desalting plant. Model results show that the Ciénega ecosystem is more sensitive to changes in salinity than to changes in flow. However, in almost all cases, an increase in salinity and/or a decrease in flow would cause a significant decrease in vegetation cover, compromising a large portion of the habitat currently available to wildlife at the Ciénega. © 2010 Elsevier B.V. All rights reserved.
• Hultine, K. R., Nagler, P. L., Morino, K., Bush, S. E., Burtch, K. G., Dennison, P. E., Glenn, E. P., & Ehleringer, J. R. (2010). Sap flux-scaled transpiration by tamarisk (Tamarix spp.) before, during and after episodic defoliation by the saltcedar leaf beetle (Diorhabda carinulata). Agricultural and Forest Meteorology, 150(11), 1467-1475.
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  Abstract: The release of the saltcedar beetle (Diorhabda carinulata) has resulted in the periodic defoliation of tamarisk (Tamarix spp.) along more than 1000 river km in the upper Colorado River Basin and is expected to spread along many other river reaches throughout the upper basin, and possibly into the lower Colorado River Basin. Identifying the impacts of these release programs on tamarisk water use and subsequent water cycling in arid riparian systems are largely unknown, due in part to the difficulty of measuring water fluxes in these systems. We used lab-calibrated, modified heat-dissipation sap flux sensors to monitor tamarisk water use (n=20 trees) before, during and after defoliation by the saltcedar leaf beetle during the 2008 and 2009 growing seasons (May-October) in southeastern Utah. We incorporated a simple model that related mean stem sap flux density (Js) with atmospheric vapor pressure deficit (vpd) before the onset of defoliation in 2008. The model was used to calculate differences between predicted Js and Js measured throughout the two growing seasons. Episodic defoliation resulted in a 16% reduction in mean annual rates of Js in both 2008 and 2009, with decreases occurring only during the periods in which the trees were defoliated (about 6-8 weeks per growing season). In other words, rates of Js rebounded to values predicted by the model when the trees produced new leaves after defoliation. Sap flux data were scaled to stand water use by constructing a tamarisk-specific allometric equation to relate conducting sapwood area to stem diameter, and by measuring the size distribution of stems within the stand. Total water use in both years was 0.224m, representing a reduction of about 0.04myr-1. Results showed that repeated defoliation/refoliation cycles did not result in a progressive decrease in either leaf production or water use over the duration of the study. This investigation improves ground-based estimates of tamarisk water use, and will support future efforts to characterize impacts of the beetle on basin-wide hydrologic processes. © 2010 Elsevier B.V.
• Alhammadi, M. S., & Edward, G. P. (2009). Effect of salinity on growth of twelve cultivars of the United Arab Emirates Date Palm. Communications in Soil Science and Plant Analysis, 40(15-16), 2372-2388.
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  Abstract: To successfully use salt water for crop production and start a breeding program, more information is needed about the response of salt-tolerant plants to saline environments. The objective of this experiment was to test the growth of 12 cultivars of the United Arab Emirates date palm seeds at four sodium chloride (NaCl) levels. The experiment was a randomized complete block design with three replicates. Optimal growth was found at control and 3000 ppm of NaCl. Relative growth rate (RGR), biomass, and number of leaves (NL) decreased significantly by increasing salinity. Increased NaCl leads to significant decreases in potassium (K+), magnesium (Mg2+), and calcium (Ca2+) contents of plants. The Na/K ratios were lower in shoots than in roots. 'Lulu,' 'Fard,' 'Khnaizi,' 'Nabtat Safi,' and 'Razez' cultivars showed greater RGR and biomasses, whereas 'Khnaizi,' 'Mesally,' and 'Safri' had greater Na/K ratios than others in the control indicating greater Na+ discriminations from plant parts. © Taylor & Francis Group, LLC.
• Carroll, K. C., Jordan, F. L., Glenn, E. P., Waugh, W. J., & Brusseau, M. L. (2009). Comparison of nitrate attenuation characterization methods at the Uranium mill tailing site in Monument Valley, Arizona. Journal of Hydrology, 378(1-2), 72-81.
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  Abstract: Several methods for characterizing the occurrence and rate of nitrate attenuation were tested at a field site near Monument Valley, Arizona. Spatial and temporal nitrate concentration data collected from a transect of monitoring wells located along the plume centerline were analyzed to evaluate the overall rates of natural attenuation. The occurrence and rate of denitrification was evaluated through microcosm experiments, nitrogen isotopic fractionation analysis, and solute-transport modeling. First-order denitrification-rate coefficients calculated with each method were comparable. In addition, the composite natural attenuation rate coefficient was similar to the denitrification-rate coefficients, which suggests that microbially induced decay primarily controls nitrate attenuation at the site. This research highlights the benefits associated with a multiple-method approach for the characterization of natural attenuation. © 2009 Elsevier B.V. All rights reserved.
• Dennison, P. E., Nagler, P. L., Hultine, K. R., Glenn, E. P., & Ehleringer, J. R. (2009). Remote monitoring of tamarisk defoliation and evapotranspiration following saltcedar leaf beetle attack. Remote Sensing of Environment, 113(7), 1462-1472.
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  Abstract: Tamarisk (Tamarix spp.) has invaded riparian ecosystems throughout the Western United States, including significant portions of riparian ecosystems within U.S. National Parks and Monuments. Recently, the saltcedar leaf beetle (Diorhabda elongata) was released as a tamarisk biocontrol agent. Although initial releases have been monitored, no comprehensive program is currently in place to monitor the rapid spread of Diorhabda that has resulted from numerous subsequent releases by county and state agencies. Long term monitoring of tamarisk defoliation and its impacts on habitat and water resources is needed. This study examines the potential for using higher spatial resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data and lower spatial resolution Moderate Resolution Imaging Spectroradiometer (MODIS) data for monitoring defoliation caused by Diorhabda and subsequent changes in evapotranspiration (ET). Widespread tamarisk defoliation was observed in an eastern Utah study area during summer 2007. ASTER normalized difference vegetation index (NDVI) showed only minor changes between 2005 and 2006, but a significant drop in NDVI was found within riparian areas between 2006 and 2007. The decrease in NDVI caused by defoliation was apparent despite partial refoliation within the study area. MODIS time series data revealed that absolute decline in EVI varied by site, but that the timing of EVI decline during summer 2007 was early with respect to phenological patterns from 2001 through 2006. Defoliation caused decreases in ET values estimated from both ASTER and MODIS data. MODIS estimated ET declined earlier than in previous years, although annual ET was not significantly different than ET in previous years due to high year-to-year variability. Challenges to detection and monitoring of tamarisk defoliation include spectral mixing of tamarisk and other cover types at subpixel spatial resolution, spatial coregistration of time series images, the timing of image acquisition, and changes unrelated to defoliation in non-tamarisk land cover over time. Continued development of the techniques presented in this paper may allow monitoring the spread of Diorhabda and assessment of potential water salvage resulting from biocontrol of tamarisk. © 2009 Elsevier Inc.
• Glenn, E. P., Mckeon, C., Gerhart, V., Nagler, P. L., Jordan, F., & Artiola, J. (2009). Deficit irrigation of a landscape halophyte for reuse of saline waste water in a desert city. Landscape and Urban Planning, 89(3-4), 57-64.
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  Abstract: Saline waste waters from industrial and water treatment processes are an under-utilized resource in desert urban environments. Management practices to safely use these water sources are still in development. We used a deeprooted native halophyte, Atriplex lentiformis (quailbush), to absorb mildly saline effluent (1800 mg l-1 total dissolved solids, mainly sodium sulfate) from a water treatment plant in the desert community of Twentynine Palms, California. We developed a deficit irrigation strategy to avoid discharging water past the root zone to the aquifer. The plants were irrigated at about one-third the rate of reference evapotranspiration (ETo) calculated from meteorological data over five years and soil moisture levels were monitored to a soil depth of 4.7 m at monthly intervals with a neutron hydroprobe. The deficit irrigation schedule maintained the soil below field capacity throughout the study. Water was presented on a more or less constant schedule, so that the application rates were less than ETo in summer and equal to or slightly greater than ETo in winter, but the plants were able to consume water stored in the profile in winter to support summer ET. Sodium salts gradually increased in the soil profile over the study but sulfate levels remained low, due to formation of gypsum in the calcic soil. The high salt tolerance, deep roots, and drought tolerance of desert halophytes such as A. lentiformis lend these plants to use as deficit-irrigated landscape plants for disposal of effluents in urban setting when protection of the aquifer is important. © 2008 Elsevier B.V.
• Glenn, E. P., Nagler, P. L., Brusca, R. C., & Hinojosa-Huerta, O. (2009). Erratum: Coastal wetlands of the northern Gulf of California: Inventory and conservation status (Aquatic Conservation: Marine and Freshwater Ecosystems (2006) 16 (5-28) 10.1002/aqc.1059). Aquatic Conservation: Marine and Freshwater Ecosystems, 19(6), 729-.
• Jordan, F. L., Yoklic, M., Morino, K., Brown, P., Seaman, R., & Glenn, E. P. (2009). Consumptive water use and stomatal conductance of Atriplex lentiformis irrigated with industrial brine in a desert irrigation district. Agricultural and Forest Meteorology, 149(5), 899-912.
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  Abstract: The halophyte forage shrub, Atriplex lentiformis (quailbush), was irrigated with brine from a reverse-osmosis (RO) water treatment plant in an agricultural district in Marana, Arizona, in the Sonoran Desert, U.S. Small transplants were installed in large, outdoor drainage lysimeters and drip-irrigated with RO concentrate, on a schedule designed to deliver 1.5 times the reference evapotranspiration (ET0) on a daily basis, as determined by an on-site micrometeorological station. Water consumption was measured by a water-balance approach over an annual cycle and by measuring sap flow with heat-balance sensors over a 28-day period in August 2008. Over this annual cycle, biomass yield was 1.62 kg m-2 and the average water consumption during the growing season was 1.55 times ET0, similar to values for high-biomass crops such as alfalfa. The drainage fraction (water that exited lysimeters) was only 5% of the total input (irrigation plus precipitation) over the study. The Priestley-Taylor coefficient relating evapotranspiration (ET) to net radiation was 1.34, typical of values for freely transpiring crops under non-water-limiting conditions. Rates of transpiration measured by sap flow sensors were closely coupled to both solar radiation and atmospheric water demand on hourly and daily time steps. Stomatal conductance was high throughout the day and coupled to diurnal solar radiation. Although halophytes often exhibit low to moderate growth potential under natural conditions or in sub-optimal agricultural settings, the present results show that they have high growth potential when water and nutrients are not limiting. The high yield and consumptive water use by A. lentiformis makes it a good candidate for the reuse of industrial or agricultural brines in arid-zone irrigation districts. © 2008 Elsevier B.V. All rights reserved.
• Murray, R. S., Nagler, P. L., Morino, K., & Glenn, E. P. (2009). An empirical algorithm for estimating agricultural and riparian evapotranspiration using MODIS enhanced vegetation index and ground measurements of ET. II. application to the lower Colorado river, U.S.. Remote Sensing, 1(4), 1125-1138.
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  Abstract: Large quantities of water are consumed by irrigated crops and riparian vegetation in western U.S. irrigation districts. Remote sensing methods for estimating evaporative water losses by soil and vegetation (evapotranspiration, ET) over wide river stretches are needed to allocate water for agricultural and environmental needs. We used the Enhanced Vegetation Index (EVI) from MODIS sensors on the Terra satellite to scale ET over agricultural and riparian areas along the Lower Colorado River in the southwestern U.S., using a linear regression equation between ET of riparian plants and alfalfa measured on the ground, and meteorological and remote sensing data, with an error or uncertainty of about 20%. The algorithm was applied to irrigation districts and riparian areas from Lake Mead to the U.S./Mexico border. The results for agricultural crops were similar to results produced by crop coefficients developed for the irrigation districts along the river. However, riparian ET was only half as great as crop coefficient estimates set by expert opinion, equal to about 40% of reference crop evapotranspiration. Based on reported acreages in 2007, agricultural crops (146,473 ha) consumed 2.2 × 109 m3 yr--1 of water. All riparian shrubs and trees (47,014 ha) consumed 3.8 × 108 m3 yr-1, of which saltcedar, the dominant riparian shrub (25,044 ha), consumed 1.8 × 108 m3 yr-1, about 1% of the annual flow of the river. This method could supplement existing protocols for estimating ET by providing an estimate based on the actual state of the canopy as determined by frequent-return satellite data. © 2009 by the authors; licensee Molecular Diversity Preservation International, Basel, Switzerland.
• Nagler, P. L., Glenn, E. P., & Hinojosa-Huerta, O. (2009). Synthesis of ground and remote sensing data for monitoring ecosystem functions in the Colorado River Delta, Mexico. Remote Sensing of Environment, 113(7), 1473-1485.
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  Abstract: The delta of the Colorado River in Mexico supports a rich mix of estuarine, wetland and riparian ecosystems that provide habitat for over 350 species of birds as well as fish, marine mammals, and other wildlife. An important part of the delta ecosystem is the riparian corridor, which is supported by agricultural return flows and waste spills of water originating in the U.S. and Mexico. These flows may be curtailed in the future due to climate change and changing land use practices (out-of-basin water transfers, increased agricultural efficiency, and more optimal management of dams) in the U.S. and Mexico, and resource managers need to monitor the effects of their water management practices on these ecosystems. We developed ground-validated, remote sensing methods to monitor the vegetation status, habitat value, and water use of wetland and riparian ecosystems using multi-temporal, multi-resolution images. The integrated methodology allowed us to project species composition, leaf area index, fractional cover, habitat value, and evapotranspiration over seasons and years throughout the delta, in response to variable water flows from the U.S. to Mexico. Waste spills of water from the U.S. have regenerated native cottonwood and willow trees in the riparian corridor and created backwater and marsh areas that support birds and other wildlife. However, the main source of water supporting the riparian vegetation is the regional aquifer recharged by underflow from U.S. and Mexico irrigation districts. Native trees have a short half-life in the riparian zone due to human-set fires and harvesting for timber. Active management, monitoring, and restoration programs are needed to maintain the habitat value of this ecosystem for the future.
• Nagler, P. L., Morino, K., Didan, K., Erker, J., Osterberg, J., Hultine, K. R., & Glenn, E. P. (2009). Wide-area estimates of saltcedar (Tamarix spp.) evapotranspiration on the lower Colorado River measured by heat balance and remote sensing methods. Ecohydrology, 2(1), 18-33.
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  Abstract: In many places along the lower Colorado River, saltcedar (Tamarix spp) has replaced the native shrubs and trees, including arrowweed, mesquite, cottonwood and willows. Some have advocated that by removing saltcedar, we could save water and create environments more favourable to these native species. To test these assumptions we compared sap flux measurements of water used by native species in contrast to saltcedar, and compared soil salinity, ground water depth and soil moisture across a gradient of 200-1500 m from the river's edge on a floodplain terrace at Cibola National Wildlife Refuge (CNWR). We found that the fraction of land covered (fc) with vegetation in 2005-2007 was similar to that occupied by native vegetation in 1938 using satellite-derived estimates and reprocessed aerial photographs scaled to comparable spatial resolutions (3-4 m). We converted fc to estimates of leaf area index (LAI) through point sampling and destructive analyses (r2 = 0.82). Saltcedar LAI averaged 2.54 with an fc of 0.80, and reached a maximum of 37 with an f c of 0.95. The ranges in fc and LAI are similar to those reported for native vegetation elsewhere and from the 1938 photographs over the study site. On-site measurements of water use and soil and aquifer properties confirmed that although saltcedar grows in areas where salinity has increased much better than native shrubs and trees, rates of transpiration are similar. Annual water use over CNWR was about 1.15 m year-1. Copyright © 2008 John Wiley & Sons, Ltd.
• Nagler, P. L., Morino, K., Murray, R. S., Osterberg, J., & Glenn, E. P. (2009). An empirical algorithm for estimating agricultural and riparian evapotranspiration using MODIS enhanced vegetation index and ground measurements of ET. I. Description of method. Remote Sensing, 1(4), 1273-1297.
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  Abstract: We used the Enhanced Vegetation Index (EVI) from MODIS to scale evapotranspiration (ETactual) over agricultural and riparian areas along the Lower Colorado River in the southwestern US. Ground measurements of ETactual by alfalfa, saltcedar, cottonwood and arrowweed were expressed as fraction of potential (reference crop) ETo (EToF) then regressed against EVI scaled between bare soil (0) and full vegetation cover (1.0) (EVI*). EVI* values were calculated based on maximum and minimum EVI values from a large set of riparian values in a previous study. A satisfactory relationship was found between crop and riparian plant EToF and EVI*, with an error or uncertainty of about 20% in the mean estimate (mean ETactual = 6.2 mm d-1, RMSE = 1.2 mm d-1). The equation for ETactual was: ETactual = 1.22 × ETo-BC × EVI*, where ETo-BC is the Blaney Criddle formula for ETo. This single algorithm applies to all the vegetation types in the study, and offers an alternative to ETactual estimates that use crop coefficients set by expert opinion, by using an algorithm based on the actual state of the canopy as determined by time-series satellite images. © 2009 by the authors; licensee Molecular Diversity Preservation International, Basel, Switzerland.
• Nelson, S. G., Glenn, E. P., Moore, D., & Ambrose, B. (2009). Growth and distribution of the macroalgae gracilaria salicomia and G. parvispora (rhodophyta) established from aquaculture introductions at Moloka'i, Hawai'i. Pacific Science, 63(3), 383-396.
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  Abstract: Gracilaria salicornia and G. parvispora were introduced to the south reef of Moloka'i, Hawai'i, in the past 15-20 yr for aquaculture development. Both species have naturalized on the reef. Gracilaria salicornia is now considered an invasive species on O'ahu due to its tendency to grow in dense beds that produce undesirable windrows of thalli on the beach. There is also concern that it reduces biodiversity and degrades habitats of reefs. We surveyed the south coast of Moloka'i, where both species were introduced, and measured biomass density, growth rates, and thallus nutrient contents of G. salicornia in established beds. Both species are found in the silt-laden, nearshore zone of the reef within 50 m of shore. Gracilaria salicornia grows in dense beds containing 475 g dry weight m-2 of biomass, but growth rates are low, 0.03%-1.28% day -1. Tissue nitrogen levels are low, suggesting that these populations are nitrogen limited. Nevertheless, populations of G. salicornia persist and grow slowly on the reef, whereas those of G. parvsipora are only found in areas of local nitrogen enrichment from anthropogenic sources. Currently, G. salicornia does not appear to be negatively affecting the reef ecology on Moloka'i, because it is confined to the disturbed, nearshore zone. However, its ability to grow slowly and persist under low-nitrogen conditions allows it to form dense beds and suggests that it will eventually spread farther along the coast. © 2009 by University of Hawai'i Press All rights reserved.
• Scott, M. L., Nagler, P. L., Glenn, E. P., Valdes-Casillas, C., Erker, J. A., Reynolds, E. W., Shafroth, P. B., Gomez-Limon, E., & Jones, C. L. (2009). Assessing the extent and diversity of riparian ecosystems in Sonora, Mexico. Biodiversity and Conservation, 18(2), 247-269.
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  Abstract: Conservation of forested riparian ecosystems is of international concern. Relatively little is known of the structure, composition, diversity, and extent of riparian ecosystems in Mexico. We used high- and low-resolution satellite imagery from 2000 to 2006, and ground-based sampling in 2006, to assess the spatial pattern, extent, and woody plant composition of riparian forests across a range of spatial scales for the state of Sonora, Mexico. For all 3rd and higher order streams, river bottomlands with riparian forests occupied a total area of 2,301 km2. Where forested bottomlands remained, on average, 34% of the area had been converted to agriculture while 39% remained forested. We estimated that the total area of riparian forest along the principal streams was 897 km2. Including fencerow trees, the total forested riparian area was 944 km2, or 0.5% of the total land area of Sonora. Ground-based sampling of woody riparian vegetation consisted of 92, 50 m radius circular plots. About 79 woody plant species were noted. The most important tree species, based on cover and frequency, were willow species Salix spp. (primarily S. goodingii and S. bonplandiana), mesquite species Prosopis spp. (primarily P. velutina), and Fremont cottonwood Populus fremontii. Woody riparian taxa at the reach scale showed a trend of increasing diversity from north to south within Sonora. Species richness was greatest in the willow-bald cypress Taxodium distichum var. mexicanum-Mexican cottonwood P. mexicana subsp. dimorphia ecosystem. The non-native tamarisk Tamarix spp. was rare, occurring at just three study reaches. Relatively natural stream flow patterns and fluvial disturbance regimes likely limit its establishment and spread. © 2008 Springer Science + Business Media BV.
• Stromberg, J. C., Chew, M. K., Nagler, P. L., & Glenn, E. P. (2009). Changing perceptions of change: The role of scientists in tamarix and river management. Restoration Ecology, 17(2), 177-186.
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  Abstract: Initially introduced to western United States to provide ecosystem services such as erosion control, Tamarix by the mid-1900s had became vilified as a profligate waster of water. This large shrub continues, today, to be indicted for various presumed environmental and economic costs, and millions of dollars are expended on its eradication. In this review, we examine the role of scientists in driving changes in perceptions of Tamarix from valuable import to vilified invader and (in some instances) back to a productive member of riparian plant communities. Scientists over the years have sustained a negative perception of Tamarix by, among other things, (1) citing outmoded sources; (2) inferring causation from correlative studies; (3) applying conclusions beyond the scope (domain) of the studies; and (4) emphasizing findings that present the species as an extreme or unnatural agent of change. Recent research is challenging the prevailing dogma regarding Tamarix 's role in ecosystem function and habitat degradation and many scientists now recommend management shifts from "pest plant" eradication to systemic, process-based restoration. However, prejudice against this and other non-native species persists. To further close the gap between science and management, it is important for scientists to strive to (1) cite sources appropriately; (2) avoid reflexive antiexotic bias; (3) avoid war-based and pestilence-based terminology; (4) heed the levels of certainty and the environmental domain of studies; (5) maintain up-to-date information on educational Web sites; and (6) prior to undertaking restoration or management actions, conduct a thorough and critical review of the literature. © 2009 Society for Ecological Restoration International.
• Alhammadi, M. S., & Glenn, E. P. (2008). Detecting date palm trees health and vegetation greenness change on the eastern coast of the United Arab Emirates using SAVI. International Journal of Remote Sensing, 29(6), 1745-1765.
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  Abstract: Due to shortage of fresh water resources, the vegetation of the eastern region of the United Arab Emirates (UAE) has experienced a series of declines resulting from salinization of groundwater, which is the major source of irrigation. To assess these changes, field measurements combined with Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) based Soil Adjusted Vegetation Index (SAVI) were analysed. TM and ETM+ images from two dates, 1987 and 2000 were acquired to enable the computation of the greenness anomalies for three sites in the eastern region, Fujairah, Kalba and Hatta. The results show an overall increase in agricultural area, associated with a severe decrease in vegetation greenness and health conditions, particularly in the Kalba study area. The SAVI values decreased with increased soil salinity, permitting the identification of salt-affected areas. This remotely sensed data offered valuable information regarding vegetation health conditions, especially when using greenness indices. However, in open canopies, like date palm trees, soil line indices, such as, SAVI are more robust, since they account for the contribution of the soil background. This research suggests, that in order for the date palm trees of this region to stay productive, considerable attention needs to be placed in managing and monitoring soil salinity conditions and progress. Potential areas of further research range from studying the effects of tree spacing and understory crops as immediate and potential solutions to maintain productivity and mitigate the salinity problem.
• Glenn, E. P., Hucklebridge, K., Hinojosa-Huerta, O., Nagler, P. L., & Pitt, J. (2008). Reconciling environmental and flood control goals on an arid-zone river: Case study of the Limitrophe region of the Lower Colorado River in the United States and Mexico. Environmental Management, 41(3), 322-335.
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  PMID: 18167018;Abstract: Arid zone rivers have highly variable flow rates, and flood control projects are needed to protect adjacent property from flood damage. On the other hand, riparian corridors provide important wildlife habitat, especially for birds, and riparian vegetation is adapted to the natural variability in flows on these rivers. While environmental and flood control goals might appear to be at odds, we show that both goals can be accommodated in the Limitrophe Region (the shared border between the United States and Mexico) on the Lower Colorado River. In 1999, the International Boundary and Water Commission proposed a routine maintenance project to clear vegetation and create a pilot channel within the Limitrophe Region to improve flow capacity and delineate the border. In 2000, however, Minute 306 to the international water treaty was adopted, which calls for consideration of environmental effects of IBWC actions. We conducted vegetation and bird surveys within the Limitrophe and found that this river segment is unusually rich in native cottonwood and willow trees, marsh habitat, and resident and migratory birds compared to flow-regulated segments of river. A flood-frequency analysis showed that the existing levee system can easily contain a 100 year flood even if vegetation is not removed, and the existing braided channel system has greater carrying capacity than the proposed pilot channel. © 2007 Springer Science+Business Media, LLC.
• Glenn, E. P., Huete, A. R., Nagler, P. L., & Nelson, S. G. (2008). Relationship between remotely-sensed vegetation indices, canopy attributes and plant physiological processes: What vegetation indices can and cannot tell us about the landscape. Sensors, 8(4), 2136-2160.
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  Abstract: Vegetation indices (VIs) are among the oldest tools in remote sensing studies. Although many variations exist, most of them ratio the reflection of light in the red and NIR sections of the spectrum to separate the landscape into water, soil, and vegetation. Theoretical analyses and field studies have shown that VIs are near-linearly related to photosynthetically active radiation absorbed by a plant canopy, and therefore to lightdependent physiological processes, such as photosynthesis, occurring in the upper canopy. Practical studies have used time-series VIs to measure primary production and évapotranspiration, but these are limited in accuracy to that of the data used in ground truthing or calibrating the models used. VIs are also used to estimate a wide variety of other canopy attributes that are used in Soil-Vegetation-Atmosphere Transfer (SVAT), Surface Energy Balance (SEB), and Global Climate Models (GCM). These attributes include fractional vegetation cover, leaf area index, roughness lengths for turbulent transfer, emissivity and albedo. However, VIs often exhibit only moderate, non-linear relationships to these canopy attributes, compromising the accuracy of the models. We use case studies to illustrate the use and misuse of VIs, and argue for using VIs most simply as a measurement of canopy light absorption rather than as a surrogate for detailed features of canopy architecture. Used this way, VIs are compatible with "Big Leaf SVAT and GCMs that assume that canopy carbon and moisture fluxes have the same relative response to the environment as any single leaf, simplifying the task of modeling complex landscapes. © 2008 by MDPI.
• Jordan, F., Waugh, W. J., Glenn, E. P., Sam, L., Thompson, T., & Thompson, T. L. (2008). Natural bioremediation of a nitrate-contaminated soil-and-aquifer system in a desert environment. Journal of Arid Environments, 72(5), 748-763.
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  Abstract: Mining activities are a major source of land degradation in arid regions, and remediation methods developed for mesic sites may not be appropriate for arid sites. In climates where potential evapotranspiration exceeds precipitation, it might be possible to prevent the migration of contaminants away from a mine site by controlling the site water balance through vegetation, and allowing natural attenuation processes to reduce pollutant levels over time. We investigated the feasibility of remediating a nitrate-contaminated source-plume system in a desert environment using biological methods. The study site was a former uranium mill in Monument Valley, Arizona, where NO3- used in ore processing had leaked from the soil beneath a tailings pile (referred to as the source area) into an alluvial aquifer (referred to as the plume) spreading away from the source area. We used 15N/14N ratios and direct assays of denitrification to show that biological denitrification occurred in both the source area and plume, and could reduce NO3- levels over time. Denitrification in the source area could be stimulated by providing additional moisture to the soil through irrigation, whereas providing a carbon source (ethanol) stimulated denitrification in samples from the plume. We used 18O/16O and H/deuterium signatures in water and plant samples to show that the native saltbush (Atriplex canescens) and black greasewood (Sarcobatus vermiculatus) plant community was extracting water from the plume, offering a possible means of preventing migration of the plume by controlling grazing over the site. We conclude that biological remediation is a feasible alternative to pump/treat solutions at this type of site. © 2007 Elsevier Ltd. All rights reserved.
• Karim, M. R., Glenn, E. P., & Gerba, C. P. (2008). The effect of wetland vegetation on the survival of Escherichia coli, Salmonella typhimurium, bacteriophage MS-2 and polio virus. Journal of Water and Health, 6(2), 167-175.
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  PMID: 18209279;Abstract: A study was conducted to examine the role of aquatic plants used in constructed wetlands on the survival of enteric bacteria and viruses. Four small-scale wetland systems, receiving fresh water and two other wetland systems, receiving secondary unchlorinated sewage were used in this study. Fresh water and secondary sewage without the presence of any aquatic plants were used as controls. Escherichia coli, Salmonella typhimurium, bacteriophage MS-2 and poliovirus were added to the waters collected from the wetlands and controls. The presence of aquatic plants significantly increased the die-off of both bacteria in fresh water and secondary sewage. No significant difference in the die-off of E. coli and S. typhimurium was observed in water from wetlands with different types of plants in freshwater. However, there was a significant difference in the die-off of E. coli in water with aquatic plants when sewage was used. The presence of the plants significantly increased the inactivation of MS-2 and poliovirus. Additional work on the survival of E. coli indicated that the plausible mechanism of bacterial die-off in constructed wetlands is through increased microbial competition or predation. © IWA Publishing 2008.
• Nagler, P. L., Glenn, E. P., Didan, K., Osterberg, J., Jordan, F., & Cunningham, J. (2008). Wide-area estimates of stand structure and water use of tamarix spp. on the lower colorado river: Implications for restoration and water management projects. Restoration Ecology, 16(1), 136-145.
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  Abstract: Tamarix spp. removal has been proposed to salvage water and allow native vegetation to recolonize western U.S. riparian corridors. We conducted wide-area studies on the Lower Colorado River to answer some of the scientific questions about Tamarix water use and the consequences of removal, combining ground surveys with remote sensing methods. Tamarix stands had moderate rates of evapotranspiration (ET), based on remote sensing estimates, averaging 1.1 m/yr, similar to rates determined for other locations on the river and other rivers. Leaf area index values were also moderate, and stands were relatively open, with areas of bare soil interspersed within stands. At three Tamarix sites in the Cibola National Wildlife Refuge, groundwater salinity at the site nearest to the river (200 m) was relatively low (circa 2,250 mg/L) and was within 3 m of the surface. However, 750 and 1,500 m from the river, the groundwater salinity was 5,000-10,000 mg/L due to removal of water by the Tamarix stands. Despite the high groundwater salinity, the sites away from the river did not have saline surface soils. Only 1% of the mean annual river flow is lost to Tamarix ET on the Lower Colorado River in the United States, and the opportunities for water salvage through Tamarix removal are constrained by its modest ET rates. A possible alternative to Tamarix removal is to intersperse native plants among the stands to improve the habitat value of the riparian zone. © 2008 Society for Ecological Restoration International.
• Nagler, P. L., Glenn, E. P., Hinojosa-Huerta, O., Zamora, F., & Howard, K. (2008). Riparian vegetation dynamics and evapotranspiration in the riparian corridor in the delta of the Colorado River, Mexico. Journal of Environmental Management, 88(4), 864-874.
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  PMID: 17590498;Abstract: Like other great desert rivers, the Colorado River in the United States and Mexico is highly regulated to provide water for human use. No water is officially allotted to support the natural ecosystems in the delta of the river in Mexico. However, precipitation is inherently variable in this watershed, and from 1981-2004, 15% of the mean annual flow of the Lower Colorado River has entered the riparian corridor below the last diversion point for water in Mexico. These flows include flood releases from US dams and much smaller administrative spills released back to the river from irrigators in the US and Mexico. These flows have germinated new cohorts of native cottonwood and willow trees and have established an active aquatic ecosystem in the riparian corridor in Mexico. We used ground and remote-sensing methods to determine the composition and fractional cover of the vegetation in the riparian corridor, its annual water consumption, and the sources of water that support the ecosystem. The study covered the period 2000-2004, a flood year followed by 4 dry years. The riparian corridor occupies 30,000 ha between flood control levees in Mexico. Annual evapotranspiration (ET), estimated by Moderate Resolution Imaging Spectrometer (MODIS) satellite imagery calibrated against moisture flux tower data, was about 1.1 m yr-1 and was fairly constant throughout the study period despite a paucity of surface flows 2001-2004. Total ET averaged 3.4×108 m3 yr-1, about 15% of Colorado River water entering Mexico from the US Surface flows could have played only a small part in supporting these high ET losses. We conclude that the riparian ET is supported mainly by the shallow regional aquifer, derived from agricultural return flows, that approaches the surface in the riparian zone. Nevertheless, surface flows are important in germinating cohorts of native trees, in washing salts from the soil and aquifer, and in providing aquatic habitat, thereby enriching the habitat value of the riparian corridor for birds and other wildlife. Conservation and water management strategies to enhance the delta habitats are discussed in light of the findings. © 2007 Elsevier Ltd. All rights reserved.
• Mendez, M. O., Glenn, E. P., & Maier, R. M. (2007). Phytostabilization potential of quailbush for mine tailings: Growth, metal accumulation, and microbial community changes. Journal of Environmental Quality, 36(1), 245-253.
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  PMID: 17215233;Abstract: Abandoned mine tailings sites in semiarid regions remain unvegetated for extended periods of time and are subject to eolian dispersion and water erosion. This study examines the potential phytostabilization of a lead-zinc mine tailings site using a native, drought-tolerant halophyte, quailbush [Atriplex lentiformis (Torr.) S. Wats.]. In a greenhouse study germination, growth, and metal uptake was evaluated in two compost-amended mine tailings samples, K4 (pH 3) and K6 (pH 6) at 75, 85, 90, 95, and 100% mine tailings, and two controls, off-site and compost. Microbial community changes were monitored by performing MPN analysis of iron- and sulfur-oxidizing bacteria as well as heterotrophic plate counts. Results demonstrate that germination is not a good indicator for phytostabilization since it was only inhibited in the unamended K4 treatment Plant growth was significantly reduced in 95 and 100% mine tailings, while growth in 75, 85, and 90% treatments was similar to the off-site control. Quailbush accumulated elevated levels of the nutrient metals Na, K, Mn, and Zn in the shoot tissues; however, metal accumulation was generally below the domestic animal toxicity limit Initially, autotrophic population estimates were four to six logs higher than heterotrophic counts, indicating extremely stressed conditions. However, post-harvest, heterotrophic bacterial counts increased to normal levels (∼106 CFU g-1 dry tailings) and dominated the rhizosphere. Therefore, with compost amendment, quailbush has good potential as a native species candidate for phytostabilization of mine tailings in semiarid environments. © ASA, CSSA, SSSA.
• Nagler, P. L., Glenn, E. P., Kim, H., Emmerich, W., Scott, R. L., Huxman, T. E., & Huete, A. R. (2007). Relationship between evapotranspiration and precipitation pulses in a semiarid rangeland estimated by moisture flux towers and MODIS vegetation indices. Journal of Arid Environments, 70(3), 443-462.
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  Abstract: We used moisture Bowen ratio flux tower data and the enhanced vegetation index (EVI) from the moderate resolution imaging spectrometer (MODIS) on the Terra satellite to measure and scale evapotranspiration (ET) over sparsely vegetated grassland and shrubland sites in a semiarid watershed in southeastern Arizona from 2000 to 2004. The grassland tower site had higher mean annual ET (336 mm yr-1) than the shrubland tower site (266 mm yr-1) (P
• Nagler, P., Jetton, A., Fleming, J., Didan, K., Glenn, E., Erker, J., Morino, K., Milliken, J., & Gloss, S. (2007). Evapotranspiration in a cottonwood (Populus fremontii) restoration plantation estimated by sap flow and remote sensing methods. Agricultural and Forest Meteorology, 144(1-2), 95-110.
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  Abstract: Native tree plantations have been proposed for the restoration of wildlife habitat in human-altered riparian corridors of western U.S. rivers. Evapotranspiration (ET) by riparian vegetation is an important, but poorly quantified, term in river water budgets. Native tree restoration plots will potentially increase ET. We used sap flow sensors and satellite imagery to estimate ET in a 8 ha, cottonwood (Populus fremontii) restoration plot on the Lower Colorado River. Biometric methods were used to scale leaf area to whole trees and stands of trees. This technique was used to validate our estimates of ET obtained by scaling from branch level to stand (or plot) level measurements of ET. Cottonwood trees used 6-10 mm day-1 of water during the peak of the growing season as determined by sap flow sensors, and annual rates scaled by time-series MODIS satellite imagery were approximately 1.2 m year-1. Although irrigation was not quantified, the field had been flood irrigated at 2 week intervals during the 3 years prior to the study, receiving approximately 2 m year-1 of water. A frequency-domain electromagnetic induction survey of soil moisture content showed that the field was saturated (26-28% gravimetric water content) at the 90-150 cm soil depth under the field. Trees were apparently rooted into the saturated soil, and considerable saving of water could potentially be achieved by modifying the irrigation regime to take into account that cottonwoods are phreatophytes. The study showed that cottonwood ET can be monitored by remote sensing methods calibrated with ground measurements with an accuracy or uncertainty of 20-30% in western riparian corridors. © 2007 Elsevier B.V. All rights reserved.
• Rosario, K., Iverson, S. L., Henderson, D. A., Chartrand, S., McKeon, C., Glenn, E. P., & Maier, R. M. (2007). Bacterial community changes during plant establishment at the San Pedro River mine tailings site. Journal of Environmental Quality, 36(5), 1249-1259.
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  PMID: 17636285;Abstract: Mine tailings are moderately to severely impacted sites that lack normal plant cover, soil structure and development, and the associated microbial community. In arid and semiarid environments, tailings and their associated contaminants are prone to eolian dispersion and water erosion, thus becoming sources of metal contamination. One approach to minimize or eliminate these processes is to establish a permanent vegetation cover on tailings piles. Here we report a revegetation trial conducted at a moderately impacted mine tailings site in southern Arizona. A salt and drought-tolerant plant, four-wing saltbush [Atriplex canescens (Pursh) Nutt.], was chosen for the trial. A series of 3 by 3 m plots were established in quadruplicate on the test site to evaluate growth of four-wing saltbush transplants alone or with compost addition. Results show that >80% of the transplanted saltbush survived after 1.5 yr in both treatments. Enumeration of heterotrophs and community structure analysis were conducted to monitor bacterial community changes during plant establishment as an indicator of plant and soil health. The bacterial community was evaluated using denaturing gradient gel electrophoresis (DGGE) analysis of 16S rDNA PCR gene products from tailings samples taken beneath transplant canopies. Significant differences in heterotrophic counts and community composition were observed between the two treatments and unplanted controls throughout the trial, but treatment effects were not observed. The results suggest that compost is not necessary for plant establishment at this site and that plants, rather than added compost, is the primary factor enhancing bacterial heterotrophic counts and affecting community composition. Copyright © 2007 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.
• Banerjee, M. J., Gerhart, V. J., & Glenn, E. P. (2006). Native plant regeneration on abandoned desert farmland: Effects of irrigation, soil preparation, and amendments on seedling establishment. Restoration Ecology, 14(3), 339-348.
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  Abstract: Direct seeding methods to revegetate abandoned farmland were tested at a desert site west of Phoenix, Arizona. Native seeds were broadcast onto plots prepared by mulching, imprinting, chiseling, and fertilizing with phosphorous in a split-plot design. Each main plot was split into subplots that were not irrigated, irrigated with saline (3.25 dS/m) well water, or irrigated and hand weeded of Salsola iberica. Native seeds germinated poorly on all treatments, and three annual exotic weeds (Brassica nigra, S. iberica, and Schismus spp.) dominated the plots. None of the main plot treatments (mulching, imprinting, chiseling, or fertilizing) had a significant effect on seed germination or canopy cover. Irrigation increased plant cover on plots, but weeds dominated the cover (
• Franklin, K. A., Lyons, K., Nagler, P. L., Lampkin, D., Glenn, E. P., Molina-Freaner, F., Markow, T., & Huete, A. R. (2006). Buffelgrass (Pennisetum ciliare) land conversion and productivity in the plains of Sonora, Mexico. Biological Conservation, 127(1), 62-71.
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  Abstract: Bufflelgrass (Pennisetum ciliare syn. Cenchrus ciliaris) is an African grass that has been widely introduced in subtropical arid regions of the world to improve rangelands for cattle production. However, it can have a negative effect on the diversity of native plant communities. Buffelgrass was introduced to Sonora, Mexico in the 1970s as a means to bolster the cattle industry. "Desmonte," the process by which native desert vegetation is removed in preparation for buffelgrass seeding, alters the land surface such that buffelgrass plots are easily detectable from aerial and Landsat satellite images. We estimated the extent of conversion to buffelgrass in a 1,850,000 ha area centered on Hermosillo, from MSS and TM images from 1973, 1983, 1990 and 2000. We then compared the relative above-ground productivity of buffelgrass to native vegetation using Normalized Difference Vegetation Index values (NDVI) from Landsat and Moderate Resolution Imaging Spectrometer (MODIS) satellite sensor systems. Buffelgrass pastures have increased from just 7700 ha in 1973 to over 140,000 ha in 2000. Buffelgrass pastures now cover 8% of the land surface in the study area. Buffelgrass pastures have lower net primary productivity, estimated by MODIS NDVI values, than unconverted desert land. The desmonte process removes trees and shrubs, while the buffelgrass plantings are often sparse, leading to an apparent net loss in net primary production from land conversion. We recommend that the desmonte process be discontinued until its efficacy and safety for native ecosystems can be established, and that a comprehensive plan for preserving biodiversity while accomodating economic development be established for this region of the Sonoran Desert in Mexico. © 2005 Elsevier Ltd. All rights reserved.
• Gerhart, V. J., Kane, R., & Glenn, E. P. (2006). Recycling industrial saline wastewater for landscape irrigation in a desert urban area. Journal of Arid Environments, 67(3), 473-486.
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  Abstract: With water conservation efforts accelerating in arid environments, industrial wastewater is considered a candidate for reuse. We investigated the possibility of using high-TDS (total dissolved solids) blowdown water from cooling towers to irrigate common landscape plants in a desert, urban environment. Nine species (three desert legume trees, three xeric-adapted shrubs and three groundcovers) were planted in a replicate block design on a 0.2 ha site. Each plant was irrigated according to water demand determined by the soil moisture deficit, with one of three water treatments: blowdown water (3.65 dS m-1, 2340 mg l-1), well water (0.52 dS m-1, 335 mg l-1) and a 1:1 blend (2.09 dS m-1, 1340 mg l-1). Water uptake, plant growth rates and soil salinity were monitored over a 27 month period. Irrigation rates were reduced for the final 12 months of the study to more closely match standard landscape practices. All plants grew well over the study and irrigation salinity did not have a significant effect (p>0.05) on growth or water use. Soil salinities were higher in basins irrigated with blowdown water compared to those irrigated with well water, but soil salinities did not increase significantly over time for any treatment. Soil solution salinities on the blowdown treatment were in the range of 6400-15,000 mg l-1, showing that these species have considerable tolerance. The overall feasibility of reusing industrial brines to irrigate urban landscapes is discussed in light of the results. © 2006 Elsevier Ltd. All rights reserved.
• Glenn, E. P., Nagler, P. L., Brusca, R. C., & Hinojosa-Huerta, O. (2006). Coastal wetlands of the northern Gulf of California: Inventory and conservation status. Aquatic Conservation: Marine and Freshwater Ecosystems, 16(1), 5-28.
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  Abstract: 1. Above 28°N, the coastline of the northern Gulf of California is indented at frequent intervals by negative or inverse estuaries that are saltier at their backs than at their mouths due to the lack of freshwater inflow. These 'esteros' total over 215000 ha in area and encompass mangrove marshes below 29°N and saltgrass (Distichlis palmeri) marshes north of 29°N. An additional 6000 ha of freshwater and brackish wetlands are found in the Colorado River delta where fresh water enters the intertidal zone. 2. The mangrove marshes in the Gulf of California have been afforded some degree of protected status in Mexico, but the northern saltgrass esteros do not have priority conservation status and are increasingly becoming development targets for resorts, vacation homes and aquaculture sites. 3. We conducted an inventory of the marshes using aerial photography and satellite images, and evaluated the extent and type of development on each marsh. We reviewed the available literature on the marshes to document their vegetation types and ecological functions in the adjacent marine and terrestrial ecosystems. 4. Over 95% of the mangrove marshes have been developed for shrimp farming. However, the farms are built adjacent to, rather than in, the marshes, and the mangrove stands are still mostly intact. 5. The majority of saltgrass marshes above the mangrove line are still relatively unspoiled. However, resort and vacation home development is taking place on land surrounding them. 6. We recommend a system of protected reserves incorporating the pristine wetlands, along with water quality management and buffer zones for the more developed esteros. The saltgrass marshes should be considered for conservation protection, similar to the protection given to the southern mangrove marshes whose value has already been recognized. Copyright © 2006 John Wiley & Sons, Ltd.
• McKeon, C., Glenn, E. P., Waugh, W. J., Eastoe, C., Jordan, F., & Nelson, S. G. (2006). Growth and water and nitrate uptake patterns of grazed and ungrazed desert shrubs growing over a nitrate contamination plume. Journal of Arid Environments, 64(1), 1-21.
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  Abstract: Two native desert shrubs were evaluated for their growth potential and water and nitrogen uptake patterns over a nitrate-contaminated aquifer at a former uranium ore-processing facility in northeastern Arizona. Sarcobatus vermiculatus and Atriplex canescens are obligate and facultative phreatophytes, respectively, that dominate the local desert plant community. The main questions we addressed were: (1) Are these shrubs able to use water or nitrogen from the alluvial aquifer? (2) If so, does grazing interfere with that ability of shrubs? (3) What would be the ideal strategy to take up N from the plume and prevent its expansion and recharge using shrubs? δ18O and δD isotope signatures from water in plant stem samples suggest that both species utilize mainly deep, stored soil water derived from winter rains for transpiration, rather than summer rains or plume water. δ15N enrichment values were similar for leaves of plants growing on and off the plume and for soil and aquifer water samples, but nitrate-N levels in leaf tissues were five times higher in plants growing on the plume compared to off the plume, suggesting they may have derived at least part of their nitrogen from the contamination plume. Total leaf N was also higher for plants growing on the plume. Under present conditions, only about 5% of the area over the plume is vegetated. Plants protected from grazing inside exclosures increased in volume by 2-4-fold over three growing seasons. Transplants of A. canescens, protected from grazing and irrigated over the first summer, established readily and grew into large shrubs after 3 years. On the basis of this study, the shrub community could be increased to as high as 25% cover and could make a significant contribution to controlling recharge if the contaminated site was protected from grazing. The results suggest that deeply rooted desert shrubs can impact the subsoil water and nitrogen balance, and that this balance can be disrupted by land use practices such as overgrazing that degrade the vegetation cover. © 2005 Elsevier Ltd. All rights reserved.
• Vasquez, E. A., Glenn, E. P., Guntenspergen, G. R., Brown, J. J., & Nelson, S. G. (2006). Salt tolerance and osmotic adjustment of Spartina alterniflora (Poaceae) and the invasive M haplotype of Phragmites australis (Poaceae) along a salinity gradient. American Journal of Botany, 93(12), 1784-1790.
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  PMID: 21642124;Abstract: An invasive variety of Phragmites australis (Poaceae, common reed), the M haplotype, has been implicated in the spread of this species into North American salt marshes that are normally dominated by the salt marsh grass Spartina alterniflora (Poaceae, smooth cordgrass). In some European marshes, on the other hand, Spartina spp. derived from S. alterniflora have spread into brackish P. australis marshes. In both cases, the non-native grass is thought to degrade the habitat value of the marsh for wildlife, and it is important to understand the physiological processes that lead to these species replacements. We compared the growth, salt tolerance, and osmotic adjustment of M haplotype P. australis and S. alterniflora along a salinity gradient in greenhouse experiments. Spartina alterniflora produced new biomass up to 0.6 M NaCl, whereas P. australis did not grow well above 0.2 M NaCl. The greater salt tolerance of S. alterniflora compared with P. australis was due to its ability to use Na+ for osmotic adjustment in the shoots. On the other hand, at low salinities P. australis produced more shoots per gram of rhizome tissue than did S. alterniflora. This study illustrates how ecophysiological differences can shift the competitive advantage from one species to another along a stress gradient. Phragmites australis is spreading into North American coastal marshes that are experiencing reduced salinities, while Spartina spp. are spreading into northern European brackish marshes that are experiencing increased salinities as land use patterns change on the two continents.
• Baumgartner, D. J., Glenn, E. P., Thompson, T. L., & Skeen, B. A. (2005). Land disposal of centrate from biosolids production. Water, Air, and Soil Pollution, 162(1-4), 219-228.
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  Abstract: Arid land and riparian plants were irrigated with a liquid wastewater stream (centrate) from biosolids production at a municipal sewage treatment facility. Centrate containing approximately 1000 mg/l ammonia nitrogen was diluted with Tucson city tap water to provide treatments of 2.5, 5, 10, 25, 50, and 100% centrate, along with a dilution water control. Plants grown in 19-l containers in a greenhouse were irrigated daily with 6.7 l of solution over a 7-week period. All species exhibited a fertilizing effect at concentrations up to 5 and 10% centrate, equivalent to approximately 50 and 100 mg/l NH 3-N, but then inhibitory above 100 mg/l. No plants survived on the 50 or 100% treatments. If centrate were to be diverted from the wastewater facility to be disposed of on the land, it was estimated that the total nitrogen content of the biosolids produced by the plant would be reduced by 11%. This reduction would have only a small impact on the value of the biosolids for soil amendment applications. © Springer 2005.
• Bymers, L., Glenn, E. P., Nelson, S. G., & Fitzsimmons, K. (2005). Diversity and biomass dynamics of marine algae in Biosphere II's tropical reef macrocosm. Ecological Engineering, 25(4), 442-456.
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  Abstract: Macrocosms can be used to study complex ecological processes in a small physical space, but the validity of the studies depends on how well the macrocosm simulates natural ecosystem functions. We measured the standing crop of macroalgae and nutrient levels over 4 years in the Biosphere II macrocosm tropical reef biome at Oracle, Arizona. Ten years after this system was closed to outside introductions, it still contained 35 species of macroalgae, within the range found on natural reefs. The macroalgae community was recognizable as a late-successional, coralline algal turf community similar to those found in the low-energy portions of inner tropical reefs. However, biomass values for the most abundant species were in a continual state of flux over the study, and no single species was dominant. Nutrient levels were also unexpectedly dynamic, with dissolved inorganic phosphorous, nitrate, and ammonium each varying by a factor of 10 over the study. The dynamic nature of biomass and nutrient cycles would make it difficult to use this macrocosm for controlled studies. On the other hand, the community dynamics in the Biosphere II ocean may shed light on processes controlling biodiversity and succession on natural reefs. The apparently chaotic swings in biomass and nutrient levels suggested that the paradox of the plankton, which explains how seemingly uniform aquatic environments can support a wide diversity of planktonic forms, may apply to reef macroalgae as well. The Biosphere II ocean biome demonstrates that a diverse macroalgal reef community can be restored relatively easily, supporting the feasibility of actively restoring damaged natural reefs. Macrocosms such as this could be used in manipulative experiments to study the effects of nutrient enrichment and herbivory on coral-algal phase shifts. © 2005 Elsevier B.V. All rights reserved.
• Glenn, E. P., & Nagler, P. L. (2005). Comparative ecophysiology of Tamarix ramosissima and native trees in western U.S. riparian zones. Journal of Arid Environments, 61(3), 419-446.
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  Abstract: Over the past century, the natural flow regimes of the major western U.S. rivers have been altered by dams, flow regulation and diversion of water for human use. As a result, the floodplains of many rivers have become drier and more saline than in the pre-dam era, and riparian water tables have declined. These conditions have favored the replacement of native mesic trees such as Populus spp. (cottonwood) and Salix spp. (willow) by saltcedar, (Tamarix ramosissima), an introduced, stress-tolerant shrub from Eurasia. Saltcedar is now the dominant woody species on many perennial rivers systems in the arid southwestern U.S. and northwest Mexico A review of the research literature shows that saltcedar has greater salt tolerance, drought tolerance, resistance to water stress, and fire tolerance than mesic native trees. On the other hand, under a natural flow regime, native trees are competitive with saltcedar in germination and establishment during a flood year and they have equal or faster growth rates. On rivers that still experience a pulse flood regime or where floods have been reestablished, cottonwood and willow have shown the ability to establish despite the presence of saltcedar. Contrary to previous reviews, the current evidence does not support the conclusion that saltcedar has unusually high evapotranspiration rates or leaf area index that would allow it to dessicate water courses. According to most researchers, an effective management strategy for saltcedar must include the return of a more dynamic hydrological regime to regulated rivers, allowing saltcedar and native trees to coexist to maximize the habitat value of the riparian zone. © 2004 Elsevier Ltd. All rights reserved.
• McKeon, C. A., Jordan, F. L., Glenn, E. P., Waugh, W. J., & Nelson, S. G. (2005). Rapid nitrate loss from a contaminated desert soil. Journal of Arid Environments, 61(1), 119-136.
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  Abstract: A 1.6 ha plot of Atriplex canescens (fourwing saltbush) was established in a desert soil at a former uranium ore-processing plant, near Monument Valley, Arizona, to remediate nitrate and ammonium N contamination. The plants were irrigated to stimulate growth and N uptake. However, NO 3- loss from the soil was unexpectedly rapid. Initially, the soil contained approximately 180 mg kg -1 NO 3--N distributed at depths up to 4.6 m, but concentrations decreased to 80 mg kg -1 after 41 months. Losses occurred throughout the plot at all soil depths. NH 4-N remained unchanged (ca.180 mg kg -1). Soil moisture was generally below field capacity and soil-water flux showed no net downward movement over the course of the study. A salt balance showed a 10% decrease in soluble salts during the study, attributable to the loss in NO 3-. Residual soluble soil N became progressively enriched in 15N over time, consistent with biological denitrification. Additionally, microcosm studies indicate significant potential denitrification rates on the plot but not for control soils. Total losses of NO 3--N were 1360 kg ha -1 yr -1. These findings of rapid denitrification in the vadose zone of a desert soil are unique and may offer a low-cost method for NO 3- remediation at similar sites. These findings are also of interest due to the depth at which the losses occurred and the possibility that considerable amounts of naturally occurring NO 3- in deep vadose zone desert soils in the southwestern US could be similarly mobilized by changing land use practices or climate change. © 2004 Elsevier Ltd. All rights reserved.
• Nagler, P. L., Cleverly, J., Glenn, E., Lampkin, D., Huete, A., & Wan, Z. (2005). Predicting riparian evapotranspiration from MODIS vegetation indices and meteorological data. Remote Sensing of Environment, 94(1), 17-30.
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  Abstract: A vegetation index (VI) model for predicting evapotranspiration (ET) from data from the Moderate Resolution Imaging Spectrometer (MODIS) on the EOS-1 Terra satellite and ground meteorological data was developed for riparian vegetation along the Middle Rio Grande River in New Mexico. Ground ET measurements obtained from eddy covariance towers at four riparian sites were correlated with MODIS VIs, MODIS land surface temperatures (LSTs), and ground micrometeorological data over four years. Sites included two saltcedar (Tamarix ramosissima) and two Rio Grande cottonwood (Populus deltoides ssp. Wislizennii) dominated stands. The Enhanced Vegetation Index (EVI) was more closely correlated (r=0.76) with ET than the Normalized Difference Vegetation Index (NDVI; r=0.68) for ET data combined over sites and species. Air temperature (T a) measured over the canopy from towers was the meteorological variable that was most closely correlated with ET (r=0.82). MODIS LST data at 1- and 5-km resolutions were too coarse to accurately measure the radiant surface temperature within the narrow riparian corridor; hence, energy balance methods for estimating ET using MODIS LSTs were not successful. On the other hand, a multivariate regression equation for predicting ET from EVI and T a had an r 2=0.82 across sites, species, and years. The equation was similar to VI-ET models developed for crop species. The finding that ET predictions did not require species-specific equations is significant, inasmuch as these are mixed vegetation zones that cannot be easily mapped at the species level. © 2004 Elsevier Inc. All rights reserved.
• Nagler, P. L., Hinojosa-Huerta, O., Glenn, E. P., Garcia-Hernandez, J., Romo, R., Curtis, C., Huete, A. R., & Nelson, S. G. (2005). Regeneration of native trees in the presence of invasive saltcedar in the Colorado River Delta, Mexico. Conservation Biology, 19(6), 1842-1852.
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  Abstract: Many riparian zones in the Sonoran Desert have been altered by elimination of the normal flood regime; such changes to the flow regime have contributed to the spread of saltcedar (Tamarix ramosissma Ledeb.), an exotic, salt-tolerant shrub. It has been proposed that reestablishment of a natural flow regime on these rivers might permit passive restoration of native trees, without the need for aggressive saltcedar clearing programs. We tested this proposition in the Colorado River delta in Mexico, which has received a series of large-volume water releases from U.S. dams over the past 20 years. We mapped the vegetation of the delta riparian corridor through ground and aerial surveys (1999-2002) and satellite imagery (1992-2002) and related vegetation changes to river flood flows and fire events. Although saltcedar is still the dominant plant in the delta, native cottonwood (Populus fremontii S. Wats.) and willow (Salix gooddingii C. Ball) trees have regenerated multiple times because of frequent flood releases from U.S. dams since 1981. Tree populations are young and dynamic (ages 5-10 years). The primary cause of tree mortality between floods is fire. Biomass in the floodplain, as measured by the normalized difference vegetation index on satellite images, responds positively even to low-volume (but long-duration) flood events. Our results support the hypothesis that restoration of a pulse flood regime will regenerate native riparian vegetation despite the presence of a dominant invasive species, but fire management will be necessary to allow mature tree stands to develop. ©2005 Society for Conservation Biology.
• Nagler, P. L., Scott, R. L., Westenburg, C., Cleverly, J. R., Glenn, E. P., & Huete, A. R. (2005). Evapotranspiration on western U.S. rivers estimated using the Enhanced Vegetation Index from MODIS and data from eddy covariance and Bowen ratio flux towers. Remote Sensing of Environment, 97(3), 337-351.
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  Abstract: We combined remote sensing and in-situ measurements to estimate evapotranspiration (ET) from riparian vegetation over large reaches of western U.S. rivers and ET by individual plant types. ET measured from nine flux towers (eddy covariance and Bowen ratio) established in plant communities dominated by five major plant types on the Middle Rio Grande, Upper San Pedro River, and Lower Colorado River was strongly correlated with Enhanced Vegetation Index (EVI) values from the Moderate Resolution Imaging Spectrometer (MODIS) sensor on the NASA Terra satellite. The inclusion of maximum daily air temperatures (Ta) measured at the tower sites further improved this relationship. Sixteen-day composite values of EVI and Ta were combined to predict ET across species and tower sites (r2 = 0.74); the regression equation was used to scale ET for 2000-2004 over large river reaches with T a from meteorological stations. Measured and estimated ET values for these river segments were moderate when compared to historical, and often indirect, estimates and ranged from 851-874 mm yr- 1. ET of individual plant communities ranged more widely. Cottonwood (Populus spp.) and willow (Salix spp.) stands generally had the highest annual ET rates (1100-1300 mm yr- 1), while mesquite (Prosopis velutina) (400-1100 mm yr - 1) and saltcedar (Tamarix ramosissima) (300-1300 mm yr - 1) were intermediate, and giant sacaton (Sporobolus wrightii) (500-800 mm yr- 1) and arrowweed (Pluchea sericea) (300-700 mm yr- 1) were the lowest. ET rates estimated from the flux towers and by remote sensing in this study were much lower than values estimated for riparian water budgets using crop coefficient methods for the Middle Rio Grande and Lower Colorado River. © 2005 Elsevier Inc. All rights reserved.
• Nagler, P., Glenn, E. P., Hursh, K., Curtis, C., & Huete, A. (2005). Vegetation mapping for change detection on an arid-zone river. Environmental Monitoring and Assessment, 109(1-3), 255-274.
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  PMID: 16240202;Abstract: A vegetation mapping system for change detection was tested at the Havasu National Wildlife Refuge (HNWR) on the Lower Colorado River. A low-cost, aerial photomosaic of the 4200 ha, study area was constructed utilizing an automated digital camera system, supplemented with oblique photographs to aid in determining species composition and plant heights. Ground-truth plots showed high accuracy in distinguishing native cottonwood (Populus fremontii) and willow (Salix gooddingii) trees from other vegetation on aerial photos. Marsh vegetation (mainly cattails, Typha domengensis) was also easily identified. However, shrubby terrestrial vegetation, consisting of saltcedar (Tamarix ramosissima), arrowweed (Pluchea sericea), and mesquite trees (Prosopis spp.), could not be accurately distinguished from each other and were combined into a single shrub layer on the final vegetation map. The final map took the form of a base, shrub and marsh layer, which was displayed as a Normalized Difference Vegetation Index map from a Landsat Enhanced Thematic Mapper (ETM+) image to show vegetation intensity. Native willow and cottonwood trees were digitized manually on the photomosaic and overlain on the shrub layer in a GIS. By contrast to present, qualitative mapping systems used on the Lower Colorado River, this mapping system provides quantitative information that can be used for accurate change detection. However, better methods to distinguish between saltcedar, mesquite, and arrowweed are needed to map the shrub layer. © Springer Science + Business Media, Inc. 2005.
• Vasquez, E. A., Glenn, E. P., Brown, J. J., Guntenspergen, G. R., & Nelson, S. G. (2005). Salt tolerance underlies the cryptic invasion of North American salt marshes by an introduced haplotype of the common reed Phragmites australis (Poaceae). Marine Ecology Progress Series, 298, 1-8.
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  Abstract: A distinct, non-native haplotype of the common reed Phragmites australis has become invasive in Atlantic coastal Spartina marshes. We compared the salt tolerance and other growth characteristics of the invasive M haplotype with 2 native haplotypes (F and AC) in greenhouse experiments. The M haplotype retained 50% of its growth potential up to 0.4 M NaCl, whereas the F and AC haplotypes did not grow above 0.1 M NaCl. The M haplotype produced more shoots per gram of rhizome tissue and had higher relative growth rates than the native haplotypes on both freshwater and saline water treatments. The M haplotype also differed from the native haplotypes in shoot water content and the biometrics of shoots and rhizomes. The results offer an explanation for how the M haplotype is able to spread in coastal salt marshes and support the conclusion of DNA analyses that the M haplotype is a distinct ecotype of P. australis. © Inter-Research 2005.
• Nagler, P. L., Glenn, E. P., Thompson, T. L., & Huete, A. (2004). Leaf area index and normalized difference vegetation index as predictors of canopy characteristics and light interception by riparian species on the Lower Colorado River. Agricultural and Forest Meteorology, 125(1-2), 1-17.
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  Abstract: Leaf area index (LAI) and normalized difference vegetation index (NDVI) were compared for riparian species along a 350 km stretch of the Lower Colorado River in the United States and Mexico. The species included two native trees, cottonwood (Populus fremontii) and willow (Salix gooddingii), and two salt-tolerant shrubs, saltcedar (Tamarix ramosissima) and arrowweed (Pluchia sericea), exhibiting large differences in leaf type and canopy architecture. LAI was measured with a Licor 2000 plant canopy analyzer calibrated against biomass measurements of LAI, whereas NDVI was measured by low-level aerial photography using a DyCam digital camera with Red (R)-Blue (B)-near infrared (NIR) bands. In addition, reflectance spectra were measured for leaf samples collected from plants in the field. Leaf samples of all species had similar reflectance spectra in the visible (VIS) and NIR, hence similar NDVI values, ranging from 0.62 to 0.72 (P>0.05). LAI values of field plants varied over a relatively narrow range, with mean values of 3.50, 3.28, 2.81 and 3.69 for cottonwood, willow, saltcedar and arrowweed, respectively. However, field plants showed distinct species differences in NDVI, with the following mean values: cottonwood (0.686), willow (0.600), saltcedar (0.473) and arrowweed (0.254) (all significantly different at P
• Ryder, E., Nelson, S. G., McKeon, C., Glenn, E. P., Fitzsimmons, K., & Napolean, S. (2004). Effect of water motion on the cultivation of the economic seaweed Gracilaria parvispora (Rhodophyta) on Molokai, Hawaii. Aquaculture, 238(1-4), 207-219.
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  Abstract: A cage culture system was previously developed for the red alga Gracilaria parvispora Abbott on Molokai, HI; however, yields have shown marked variation, even among cages with identical stocking rates and fertilization treatments. Water motion, which can be affected by location and arrangement of the cages in the grow-out area, was hypothesized to be a factor contributing to the variation in yield. To examine this, the growth rates of thalli and the development of sporelings in relation to water motion were determined in replicated trials both in tanks and in small-scale field experiments. Generally, water motion had a substantial effect on both thallus growth rate and spore development. In the tank cultures of thalli, water velocities ranged up to 13.7 cm s-1, and relative growth rates (RGRs) ranged from 2.8% to 8.9% day-1. In the lagoon, water velocities ranged between 3.6 and 11.6 cm s-1. Relative growth rates of the thalli in the lagoon trials were 0.02-10.3% day-1. Sporeling density, a measure of spore development, was also significantly affected by water motion. In the tank trials, water motion ranged from near 0 to 6.50 cm s-1, and sporeling densities ranged from 1.4 cm-2 at lower water motion levels to 11.6 sporelings cm-2 at higher levels. Similar results were obtained in lagoon trials, with sporeling densities ranging from 0.2 to 6.7 cm-2. However, sporeling length was not significantly correlated with water motion. In previous trials, we have been able to achieve high sporeling densities, but elongation of sporelings has been inhibited. In the present trials, we were able to break the apparent sporeling dormancy by incubating the sporelings in tanks enriched in nutrients supplied by fish cultures. Consideration of the effects of water motion is important in designing culture systems for species of Gracilaria and other marine algae. The results also suggest that nutrients play a key role in regulating the early development of G. parvispora sporelings. © 2004 Elsevier B.V. All rights reserved.
• Langdon, C., Broecker, W. S., Hammond, D. E., Glenn, E., Fitzsimmons, K., Nelson, S. G., Peng, T., Hajdas, I., & Bonani, G. (2003). Effect of elevated CO₂ on the community metabolism of an experimental coral beef. Global Biogeochemical Cycles, 17(1), 11-1.
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  Abstract: The effect of elevated pCO2 on the metabolism of a coral reef community dominated by macroalgae has been investigated utilizing the large 2650 m3 coral reef mesocosm at the Biosphere-2 facility near Tucson, Arizona. The carbonate chemistry of the water was manipulated to simulate present-day and a doubled CO2 future condition. Each experiment consisted of a 1-2 month preconditioning period followed by a 7-9 day observational period. The pCO2 was 404 ± 63 μatm during the present-day pCO2 experiment and 658 ± 59 μatm during the elevated pCO2 experiment. Nutrient levels were low and typical of natural reefs waters (NO-3 0.5-0.9 μM, NH+4 0.4 μM, PO34- 0.07-0.09 μM). The temperature and salinity of the water were held constant at 26.5 ± 0.2°C and 34.4 ± 0.2 ppt. Photosynthetically available irradiance was 10 ± 2 during the present-day experiment and 7.4 ± 0.5 mol photons m-2 d-1 during the elevated pCO2 experiment. The primary producer biomass in the mesocosm was dominated by four species of macroalgae; Haptilon cubense, Amphiroa fragillisima, Gelidiopsis intricata and Chondria dasyphylla. Algal biomass was 10.4 mol C m-2 during the present-day and 8.7 mol C m-2 and during the elevated pCO2 experiments. As previously observed, the increase in pCO2 resulted in a decrease in calcification from 0.041 ± 0.007 to 0.006 ± 0.003 mol CaCO3 m-2 d-1. Net community production (NCP) and dark respiration did not change in response to elevated pCO2. Light respiration measured by a new radiocarbon isotope dilution method exceeded dark respiration by a factor of 1.2 ± 0.3 to 2.1 ± 0.4 on a daily basis and by 2.2 ± 0.6 to 3.9 ± 0.8 on an hourly basis. The 1.8-fold increase with increasing pCO2 indicates that the enhanced respiration in the light was not due to photorespiration. Gross production (GPP) computed as the sum of NCP plus daily respiration (light + dark) increased significantly (0.24 ± 0.03 vs. 0.32 ± 0.04 mol C m-2 d-1). However, the conventional calculation of GPP based on the assumption that respiration in the light proceeds at the same rate as the dark underestimated the true rate of GPP by 41-100% and completely missed the increased rate of carbon cycling due to elevated pCO2. We conclude that under natural, undisturbed, nutrient-limited conditions elevated CO2 depresses calcification, stimulates the rate of turnover of organic carbon, particularly in the light, but has no effect on net organic production. The hypothesis that an increase pCO2 would produce an increase in net production that would counterbalance the effect of decreasing saturation state on calcification is not supported by these data.
• Nagler, P. L., Glenn, E. P., & Thompson, T. L. (2003). Comparison of transpiration rates among saltcedar, cottonwood and willow trees by sap flow and canopy temperature methods. Agricultural and Forest Meteorology, 116(1-2), 73-89.
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  Abstract: Transpiration (Et), measured by stem sap flow gauges, and canopy and air temperature differential (Tc - Ta) of Populus fremontii (cottonwood), Salix gooddingii (willow) and Tamarix ramosissima (saltcedar) were compared to determine if remotely sensed canopy temperatures could be used to estimate Et or water stress in these trees in desert riparian zones of the United States and Mexico. Controlled experiments were conducted in which containerized plants were placed closely together and allowed to grow into a single, dense canopy over a summer in a desert climate. At the end of the growth period, two canopies of each species were measured for Et and Tc - Ta over 11 days, first under unstressed conditions then under water or salt stress. Et and Tc - Ta were significantly (P < 0.05) correlated for all species. Correlation coefficients improved when a radiation term was included in the equation predicting Et from Tc - Ta. During the non-stress part of the experiment, canopies of all three species had similar rates of Et, but saltcedar maintained higher Et rates and lower rsv than the native trees on the stress treatments. For each species, models were developed, using both meteorological data and a canopy, energy-balance equation, to predict daily Et and stomatal resistance (rsv); these models had standard errors of 15-22% when compared with measured Et over the unstressed portion of the experiment. © 2003 Elsevier Science B.V. All rights reserved.
• Nagler, P. L., Glenn, E. P., Nelson, S. G., & Napolean, S. (2003). Effects of fertilization treatment and stocking density on the growth and production of the economic seaweed Gracilaria parvispora (Rhodophyta) in cage culture at Molokai, Hawaii. Aquaculture, 219(1-4), 379-391.
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  Abstract: The edible red seaweed, Gracilaria parvispora Abbott, was pulse-fertilized in tanks containing fish-culture water or chemical fertilizer, then cultured in floating cages in a low-nutrient, ocean lagoon in Molokai, HI. Small, daily additions of ammonium sulfate and ammonium diphosphate were the only additions needed to stimulate growth. Fish-culture water was as effective as chemical fertilizer in supporting growth. Thalli fertilized for 7 days in tanks contained 2.5-5% nitrogen in tissues by the end of the treatment period; upon transfer to low-nutrient water, nitrogen content decreased to 1% as the nitrogen was mobilized to support growth. Thalli grew rapidly over the first 14 days after transfer from fertilizer tanks to the ocean, achieving relative growth rates of 8-10% day-1 and producing 39-57 g dry wt. m-2 day-1. However, by 21 days after transfer, growth ceased due to depletion of stored nutrients. The optimal stocking density was 2 kg m-3 based on growth rates. Nearly all net growth occurred in the cages rather than in the fertilizer tanks, which serve only to introduce nitrogen into the thalli. The yields obtained here are four times higher than achieved previously with this species and are comparable to high-yielding, intensive tank cultures. © 2003 Elsevier Science B.V. All rights reserved.
• Nagler, P. L., Inoue, Y., Glenn, E. P., Russ, A. L., & Daughtry, C. S. (2003). Cellulose absorption index (CAI) to quantify mixed soil-plant litter scenes. Remote Sensing of Environment, 87(2-3), 310-325.
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  Abstract: Quantification of plant litter cover on the soil surface is necessary in both agricultural and natural systems because the presence of litter influences the flow of nutrients, carbon, water, and energy in terrestrial ecosystems. Although remote sensing methods for measuring plant litter cover provide both a wider area of coverage and a more objective estimate of the spatial variability of litter than manual methods of quantifying the nongreen vegetation landscape components (e.g., litter or soil percent cover), it has been difficult to assess the efficiency of detecting partial litter cover over different soil types. The objectives of this study were (i) to acquire spectral reflectance data for four crop residues and two forest litter types in mixed scenes of soil and plant litter, (ii) to derive relationships that show the spectral variable, cellulose absorption index (CAI), as a function of the amount of litter on the soil surface, and (iii) to test whether the variability of soil background reflectance inhibits the detection of residues and/or the ability to quantify residue cover. Scenes of known amounts of plant litter covering three contrasting soils were prepared and their reflectance spectra (0.4-2.5 μm) were measured with a hyper-resolution spectroradiometer. Litter from four crop (corn, soybean, rice, and wheat) and two tree species (coniferous and deciduous) were included. The CAI (0.5(R2.0 + R2.2) - R 2.1) describes the average depth of the cellulose absorption feature at 2.1 μm in reflectance spectra. Positive values of CAI indicate the presence of cellulose. The mean CAI of the soils was -2.0 while the mean CAI of the plant litter was 5.2. CAI increased linearly for each plant litter as the amount of plant litter in the scene increased from 0% (bare soil) to 100% cover. The CAI values of mixed scenes with more than 10% litter cover were significantly larger than the CAI values of the soils. The results of this study indicate that CAI is useful for quantifying plant litter cover, even at low percent cover. © 2003 Elsevier Inc. All rights reserved.
• Hart, A. M., Lasi, F. E., & Glenn, E. P. (2002). SLODS™: Slow dissolving standards for water flow measurements. Aquacultural Engineering, 25(4), 239-252.
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  Abstract: Slow dissolving plaster standards (SLODS™) were developed to obtain integrated water flow measurements over a time scale of 20-30 days, and tested in giant clam farms in the Solomon Islands under steady flow environments. SLODS™ are composed of a gypsum plaster formulation known as Specially Prepared Gypsum (SPG). This plaster has a considerably higher compressive strength; 10000-13000 psi, compared with approximately 1000 psi for more common formulations of Plaster-of-Paris. Experimental calibrations in a water motion simulator over 12 days demonstrated a highly significant relationship between fractional weight loss (FWL) of SLODS™ per day, and water velocity (r2 = 0.96). The SLODS™ simultaneously measured water flow (over a 21 day period in August 1997) at 12 giant clam grow-out sites spread across 400 km of island archipelagoes. Mean water velocity ranged from 5 to 11 cm s-1 and significantly influenced growth of giant clams. SLODS™ compared well with the established methodology of clod cards (r = 0.69; P < 0.01), with a clear advantage in their ability to integrate water motion over an extended time period into a single measurement. A practical application of SLODS™ to aquatic research will be the development of standardized SLODS™ (produced in a variety of sizes and shapes) calibrated to different factors affecting dissolution. This will require a more detailed analysis of the performance of SLODS™ under different flow, salinity, dissolved solute's, and temperature environments. © 2002 Elsevier Science B.V. All rights reserved.
• Hinojosa-Huerta, O., Nagler, P. L., Carrillo-Guerrero, Y., Zamora-Hernández, E., García-Hernández, J., Zamora-Arroyo, F., Gillon, K., & Glenn, E. P. (2002). Andrade mesa wetlands of the all-American canal. Natural Resources Journal, 42(4), 899-914.
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  Abstract: Seepage from the All-American Canal has created a series of wetlands totaling over 6200 hectares (15,500 acres) along the U.S.-Mexico border. Over half of these are in Mexico, east of the portion of the canal that is proposed for lining, and will therefore be impacted by lack of further seepage. The Andrade Mesa Wetlands are extensive and provide high-quality bird habitat in an isolated part of the northern Colorado River delta where replacement habitat is non-existent. The loss of this critical habitat should be considered in assessing the potential environmental impacts of the canal lining project.
• Jordan, F. L., Robin-Abbott, M., Maier, R. M., & Glenn, E. P. (2002). A comparison of chelator-facilitated metal uptake by a halophyte and a glycophyte. Environmental Toxicology and Chemistry, 21(12), 2698-2704.
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  PMID: 12463567;Abstract: Phytoextraction is the use of plants to remove contaminants, in particular metals, from soil via root uptake and translocation to the shoots. Efficient phytoextraction requires high-biomass plants with efficient translocating properties. Halophytes characteristically accumulate large quantities of salts in aboveground tissue material and can have high biomass production. It has been speculated that salt-tolerant plants may also be heavy metal tolerant and, further, may be able to accumulate metals. This study compared growth and metal uptake by a halophyte, Atriplex nummularia, and a common glycophyte, Zea mays, in a mineailing contaminated soil:mulch mixture. Two chelators, ethylenediaminetetraacetic acid (EDTA) and rhamnolipid, were used to facilitate plant metal uptake. Despite a lower growth rate (2% growth/d) in the contaminated soil, the halophyte accumulated roughly the same amount of metals as the glycophyte on a mass basis (30-40 mg/kg dry wt). Neither plant, however, hyperaccumulated any of the metals tested. When treated with EDTA, specific differences in patterns of metal uptake between the two plants emerged. The halophyte accumulated significantly more Cu (2x) and Pb (1 x) in the shoots than the glycophyte, but root metal concentrations were generally higher for the glycophyte, indicating that the halophyte translocated more metal from the root to the shoot than the glycophyte. For example, Zn shoot-to-root ratios ranged from 1.4 to 2.1 for Atriplex and from 0.5 to 0.6 for Z. mays. The biodegradable chelator rhamnolipid was not effective at enhancing shoot metal concentrations, even though radiolabeled chelator was found in the shoot material of both plants. Our results suggest that halophytes, despite their slower growth rates, may have greater potentiaL to selectively phytoextract metals from contaminated soils than glycophytes.
• García-Hernández, J., Hinojosa-Huerta, O., Gerhart, V., Carrillo-Guerrero, Y., & Glenn, E. P. (2001). Willow flycatcher (Empidonax traillii) surveys in the Colorado River delta: Implications for management. Journal of Arid Environments, 49(1), 161-169.
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  Abstract: A subspecies of willow flycatcher, the south-western willow flycatcher, has become endangered in the U.S. The objective of this study was to determine the presence/absence of this subspecies in the Colorado River delta. Surveys were conducted in June-July 1999 and in May-June 2000. We detected a total of 50 birds, most likely south-western willow flycatchers, from May to June and none in July. It appears that the birds found in the delta were migrants. It is important to restore the intensively used stopover sites for the recovery of the subspecies. Additionally, we postulate a migratory, route throughout the estuaries of Sonora. © 2001 Academic Press.
• García-Hernández, J., King, K. A., Velasco, A. L., Shumilin, E., Mora, M. A., & Glenn, E. P. (2001). Selenium, selected inorganic elements, and organochlorine pesticides in bottom material and biota from the Colorado River delta. Journal of Arid Environments, 49(1), 65-89.
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  Abstract: Concentrations of selenium (Se) in bottom material ranged from 0.6 to 5.0 μg g-1, and from 0.5 to 18.3 μg g-1 in biota; 23% of samples exceeded the toxic threshold. Concentrations of DDE in biota exceeded the toxic threshold in 30% of the samples. Greater concentrations of selenium in biota were found at sites with strongly reducing conditions, no output, alternating periods of drying and flooding or dredging activities, and at sites that received water directly from the Colorado River. The smallest Se concentrations in biota were found at sites where an outflow and exposure or physical disturbance of the bottom material were uncommon. © 2001 Academic Press.
• Glenn, E. P., Lee, C., & Valdes-Casillas, C. (2001). Introduction. Journal of Arid Environments, 49(1), 1-4.
• Glenn, E. P., Waugh, W. J., Moore, D., McKeon, C., & Nelson, S. G. (2001). Revegetation of an abandoned uranium millsite on the Colorado Plateau, Arizona. Journal of Environmental Quality, 30(4), 1154-1162.
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  PMID: 11476492;Abstract: We attempted to restore native plants on disturbed sites at a former uranium mill on the Colorado Plateau near Tuba City, AZ. Four-wing saltbush [Atriplex canescens (Pursh) Nutt.] was successfully established in compacted caliche soil and in unconsolidated dune soil when transplants were irrigated through the first summer with 20 L/plant/wk. The caliche soil was ripped before planting to improve water-holding capacity. The diploid saltbush variety, angustifolia, had higher survival and growth than the common tetraploid variety, occidentalis, especially on dune soil. The angustifolia variety grew to 0.3 to 0.4 m3 per plant over 3 yr even though irrigation was provided only during the establishment year. By contrast, direct seeding of a variety of native forbs, grasses, and shrubs yielded poor results, despite supplemental irrigation throughout the first summer. In this arid environment (precipitation = 100 to 200 mm/yr), the most effective revegetation strategy is to establish keystone native shrubs, such as four-wing saltbush, using transplants and irrigation during the establishment year, rather than attempting to establish a diverse plant community all at once.
• Nagler, P. L., Glenn, E. P., & Huete, A. R. (2001). Assessment of spectral vegetation indices for riparian vegetation in the Colorado River delta, Mexico. Journal of Arid Environments, 49(1), 91-110.
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  Abstract: This study tested the relationship between three, commonly-used vegetation indices (VIs), percent vegetation cover (% cover) and leaf area index (LAI) over a complex riparian landscape in the Colorado River delta, Mexico. Our objective was to correlate vegetation and soil features with VIs using low-level aerial photography, in preparation for scaling up to analysis of vegetation features using satellite imagery. We used a three-band digital imaging camera (Dycam) to collect data from an aircraft flying at 150 m. A series of 84 images (67×100 m) were analysed. Nine of these sites were ground-truthed; the species, % cover, and LAI were determined. Measured LAI (nine sites) from tree, shrub, and groundcover categories were used to determine a global (GLAI) value for 63 images. We conducted both VIs: % cover and VIs: GLAI regression analyses. The normalized difference vegetation index (NDVI) was the VI that best predicted % cover (r2=0.837), but the soil adjusted vegetation index (SAVI) and enhanced vegetation index (EVI) gave nearly equal results (r2=0.807 and 0.796, respectively). Normalized difference vegetation index, SAVI and EVI were less useful in predicting GLAI (r2=0.73, 0.65, 0.64, respectively). Variability in GLAI was due mainly to differences in % cover among images rather than differences in LAI among vegetation types. We also measured reflectance values of the major plant types between 450 and 900 nm, and found small but significant (p
• Nelson, S. G., Glenn, E. P., Conn, J., Moore, D., Walsh, T., & Akutagawa, M. (2001). Cultivation of Gracilaria parvispora (Rhodophyta) in shrimp-farm effluent ditches and floating cages in Hawaii: A two-phase polyculture system. Aquaculture, 193(3-4), 239-248.
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  Abstract: A culture system for the commercial production of the seaweed Gracilaria parvispora using shrimp-farm effluents for fertilization and floating cage-culture for grow-out has been developed on Molokai, HI. This two-phase system produces high-quality products for direct human consumption. The mean relative growth rates (RGRs) of effluent-enriched thalli in the cage system ranged from 8.8% to 10.4% day-1, a significant increase over the growth (4.6% day-1) of thalli fertilized with inorganic fertilizer. Thalli were also grown directly in the effluent ditch, where mean growth rates of 4.7% day-1 were obtained, less than in cage-culture. In the cage-culture system, thallus nitrogen content declined without fertilization. Effluent-enriched thalli grown in the cages steadily declined in nitrogen content, to about 1%, and their C:N ratios increased to between 20 and 30. However, when nitrogen-depleted thalli were transferred to the effluent ditch for enrichment, N content rapidly increased over 5 days to approximately 3%, with a C:N ratio near 10. Benefits of this two-phase polyculture system include enhanced growth of G. parvispora and the use of effluent from commercial shrimp farms as a resource. © 2001 Elsevier Science B.V.
• Vandersande, M. W., Glenn, E. P., & Walworth, J. L. (2001). Tolerance of five riparian plants from the lower Colorado River to salinity drought and inundation. Journal of Arid Environments, 49(1), 147-159.
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  Abstract: Two greenhouse experiments were conducted to compare the effects of salt stress and water stress on four native riparian species and one invasive species collected from the lower Colorado River, Mexico. Within a drying soil at the control salinity level, Populus fremontii, Salix gooddingii and Baccharis salicifolia were able to extract water from the soil equal to that of Tamarix ramosissima and Pluchea sericea. Yet, at elevated salinity levels T. ramosissima and P. sericea exhibited a superior water-use ability. Under flooded conditions all native riparian species outperformed T. ramosissima. The results show that the invasive species T. ramosissima has a competitive advantage over native species mainly with respect to salt tolerance. This suggests that pulse flooding along the river could reduce Tamarix's competitive advantage by flushing out accumulated salts from the bankside and subjecting T. ramosissima to prolonged inundation. © 2001 Academic Press.
• Zamora-Arroyo, F., Nagler, P. L., Briggs, M., Radtke, D., Rodriquez, H., Garcia, J., Valdes, C., Huete, A., & Glenn, E. P. (2001). Regeneration of native trees in response to flood releases from the United States into the delta of the Colorado River, Mexico. Journal of Arid Environments, 49(1), 49-64.
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  Abstract: Over the past 20 years, discharge of water from the United States to the delta of the Colorado River in Mexico has regenerated native trees that now account for 23% of vegetation in a 100-km, non-perennial, stretch of river below Morelos Dam at the United States-Mexico border. The discharges are associated with the filling of Lake Powell, the last large reservoir to be constructed on the river, and with ENSO cycles that bring extra winter and spring precipitation to the watershed. The discharges below Morelos Dam produce overbank foods that germinate new cohorts of Populus fremontii and Salix gooddingii trees. Relatively little flood water from the United States is required to support a pulse flood regime that can result in regrowth of native vegetation in the delta. Based on analysis of past flows and existing tree populations, we estimate that a February-April flow of 3×109 m3 at 80-120 m3 s-1 is sufficient to germinate and establish new cohorts of native trees. However, there was a positive correlation between frequency of flows and total vegetation cover over the years 1992-1999, showing that more frequent flows would further increase vegetation cover. The results support the importance of pulse floods in restoring the ecological integrity of arid-zone rivers. © 2001 Academic Press.
• Baumgartner, D. J., Glenn, E. P., Kuehl, R. O., Thompson, T. L., Artiola, J. F., Menke, S. E., Saar, R. A., Moss, G. S., & Algharaibeh, M. A. (2000). Plant uptake response to metals and nitrate in simulated uranium mill tailings contaminated groundwater. Water, Air, and Soil Pollution, 118(1-2), 115-129.
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  Abstract: Carrots, squash, and Sudan grass were irrigated with groundwater amended with manganese, molybdenum, selenium, and uranium stock solutions to simulate a range of concentrations found at ten inactive uranium ore milling sites to determine plant tissue levels after a 90 day growth period in sand in a greenhouse. Sudan grass was also dosed with a series of nitrate concentrations. Except for squash response to uranium, all plants showed an increased accumulation of each metal, some to unacceptable levels, with increased metal concentration dose. Squash did not accumulate uranium at any dose tested. Increased nitrate in the irrigation water did not have a major influence on Sudan grass accumulation of any metal.
• Baumgartner, D. J., Glenn, E. P., Moss, G., Thompson, T. L., Artiola, J. F., & Kuehl, R. O. (2000). Effect of irrigation water contaminated with uranium mill tailings on sudan grass, Sorghum vulgare var. sudanense, and fourwing saltbush, Atriplex canescens. Arid Soil Research and Rehabilitation, 14(1), 43-57.
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  Abstract: A greenhouse experiment was carried out to estimate the effects of irrigation water quality on chemical uptake and productivity of Sudan grass (Sorghum vulgate vat. sudanense) and fourwing saltbush (Atriplex canescens). Water and soil were obtained from an inactive U ore processing site near Tuba City, Arizona. Two observation wells provided the irrigation water. One was located upgradient from the contaminated site, and was located in the center of the plume downgradient from the area contaminated by the milling operations. A 50/50 mix of the two well waters was used as a third treatment. Concentrations of Se and U in aboveground tissues of saltbush were significantly (P < 0.05) elevated when irrigated with the undiluted contaminated water, but not to unacceptable levels. In the case of Sudan grass, Mo, Se, U, NO3/--N, and S were significantly (P < 0.05) elevated in the contaminated water treatment, and all except NO3/--N were elevated with the diluted contaminated water, but again within acceptable limits, Saltbush productivity was not significantly (P > 0.05) affected by the three irrigation treatments. Sudan grass aboveground biomass results suggest that the undiluted contaminated plume water could be used for effective crop production, although productivity was significantly better with the nutrient-amended baseline water and the diluted contaminated water. Root biomass was significantly greater in the baseline water irrigation.
• Galindo-Bect, M. S., Glenn, E. P., Page, H. M., Fitzsimmons, K., Galindo-Bect, L. A., Hernandez-Ayon, J. M., Petty, R. L., Garcia-Hernandez, J., & Moore, D. (2000). Penaeid shrimp landings in the upper Gulf of California in relation to Colorado River freshwater discharge. Fishery Bulletin, 98(1), 222-225.
• García-Hernández, J., Glenn, E. P., Artiola, J., & Baumgartner, D. J. (2000). Bioaccumulation of selenium (Se) in the Cienega de Santa Clara wetland, Sonora, Mexico. Ecotoxicology and Environmental Safety, 46(3), 298-304.
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  PMID: 10903827;Abstract: The Cienega de Santa Clara, on the east side of the Colorado River delta, is a brackish wetland supported by agricultural drainage water from the United States that provides habitat for endangered fish and bird species. Bioaccumulation of selenium has created toxicity problems for wildlife in similar wetlands in the United States. This is the first selenium survey in the Cienega de Santa Clara. Ten sites were selected to collect water (dissolved), sediments (total), plants, invertebrates, and fish. Samples were collected from October 1996 to March 1997. Selenium was detected in all samples. Concentrations in water ranged from 5 to 19 μg/L and increased along a salinity gradient. Although water levels of selenium exceeded EPA criterion for protection of wildlife, levels in sediments (0.8-1.8 mg/kg), aquatic plants (0.03-0.17 mg/kg), and fish (2.5-5.1 mg/kg whole body, dry wt) did not exceed USFWS recommended levels. It is concluded from this study that the levels of selenium in water did not affect the overall health of the fish sampled. Therefore, it is important to maintain or improve the water quality entering this wetland to continue to have normal levels of Se in the food chain components. (C) 2000 Academic Press.
• Grainger, A., Smith, M. S., Squires, V. R., & Glenn, E. P. (2000). Desertification and climate change: The case for greater convergence. Mitigation and Adaptation Strategies for Global Change, 5(4), 361-377.
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  Abstract: Poor knowledge of links between desertification and global climate change is limiting funding from the Global Environment Facility for anti-desertification projects and realization of synergies between the Convention to Combat Desertification (CCD) and the Framework Convention on Climate Change (FCCC). Greater convergence between research in the two fields could overcome these limitations, improve our knowledge of desertification, and benefit four areas of global climate change studies: mitigation assessment; accounting for land cover change in the carbon budget; land surface-atmosphere interactions; and climate change impact forecasting. Convergence would be assisted if desertification were treated more as a special case in dry areas of the global process of land degradation, and stimulated by: (a) closer cooperation between the FCCC and CCD; (b) better informal networking between desertification and global climate change scientists, e.g. within the framework of the Intergovernmental Panel on Climate Change (IPCC). Both strategies would be facilitated if the FCCC and CCD requested the IPCC to provide a scientific framework for realizing the synergies between them.
• Nagler, P., Gillon, K., Pitt, J., Snape, B., & Glenn, E. (2000). Application of the US Endangered Species Act across international borders: The case of the Colorado River delta, Mexico. Environmental Science and Policy, 3(2-3), 67-72.
• Zhongjin, L. u., Glenn, E. P., & John, M. M. (2000). Salicornia bigelovii: An overview. INFORM - International News on Fats, Oils and Related Materials, 11(4), 418-423.
• Brown, J. J., & Glenn, E. P. (1999). Reuse of highly saline aquaculture effluent to irrigate a potential forage halophyte, Suaeda esteroa. Aquacultural Engineering, 20(2), 91-111.
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  Abstract: We tested the feasibility of reusing saline aquaculture effluent to produce a salt-tolerant shrub (Suaeda esteroa) with potential as a forage crop. Plants were grown in sandy loam soil, in drainage lysimeters to determine forage yield, water use and capacity for nitrogen and phosphorus uptake when irrigated with highly saline (31 ppt NaCl) effluent from a tilapia culture system. Water was applied to soil three times per week at five rates, ranging in volume from 50 to 250% of the pan evaporation rate. Plant biomass increased significantly with increasing irrigation volume (P < 0.05). Due to higher plant growth, water consumption also increased with increasing irrigation volume (P < 0.05). Nitrate concentrations in water draining from the lysimeters decreased during the experiment and decreased with increasing irrigation volume (P < 0.05). Toward the end of the experiment, concentrations of nitrate in the leachate in the high volume treatments were below the mean limits set by the US Environmental Protection Agency for effluent discharge. Phosphorus concentrations in the leachate water increased during the experiment and increased with increasing irrigation volume (P < 0.05). We conclude that using high salinity aquaculture wastewater to irrigate halophyte crops can be a viable strategy for disposal of effluent, especially where phosphorus is not a limiting nutrient.
• Brown, J. J., Glenn, E. P., Fitzsimmons, K. M., & Smith, S. E. (1999). Halophytes for the treatment of saline aquaculture effluent. Aquaculture, 175(3-4), 255-268.
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  Abstract: We determined the feasibility of using salt-tolerant plants (halophytes) as biofilters to remove nutrients from saline aquaculture wastewater. Suaeda esteroa, Salicornia bigelovii and Atriplex barclayana (Chenopodiaceae), species with potential as forage and oil seed crops, were grown in sand in draining containers (lysimeters) in a greenhouse experiment. They were irrigated to meet evapotranspiration demand and to produce a 0.3 leaching fraction, using aquaculture effluent generated from an intensive tilapia culture system. The effluent salinity was increased with NaCl to make salinity treatments of 0.5, 10 and 35 ppt. The plant-soil system removed 98% and 94% of the applied total and inorganic nitrogen, respectively. It removed 99% and 97% of the applied total and soluble reactive phosphorus, respectively. High removal rates occurred despite the high leaching fraction. Salt inhibited (P < 0.05) the growth rate, nutrient removal, and volume of water that all three plant species could process. Suaeda and Salicornia, which are succulent salt marsh species, performed better than the desert saltbush, Atriplex, at the higher salinities.
• Glenn, E. P., Brown, J. J., & Blumwald, E. (1999). Salt tolerance and crop potential of halophytes. Critical Reviews in Plant Sciences, 18(2), 227-255.
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  Abstract: Although they represent only 2% of terrestrial plant species, halophytes are present in about half the higher plant families and represent a wide diversity of plant forms. Despite their polyphyletic origins, halophytes appear to have evolved the same basic method of osmotic adjustment: accumulation of inorganic salts, mainly NaCl, in the vacuole and accumulation of organic solutes in the cytoplasm. Differences between halophyte and glycophyte ion transport systems are becoming apparent. The pathways by which Na+ and Cl- enters halophyte cells are not well understood but may involve ion channels and pinocytosis, in addition to Na+ and Cl- transporters. Na+ uptake into vacuoles requires Na+/H+ antiporters in the tonoplast and H+ ATPases and perhaps PP(i) ases to provide the proton motive force. Tonoplast antiporters are constitutive in halophytes, whereas they must be activated by NaCl in salt-tolerant glycophytes, and they may be absent from salt-sensitive glycophytes. Halophyte vacuoles may have a modified lipid composition to prevent leakage of Na+ back to the cytoplasm. Because of their diversity, halophytes have been regarded asa rich source of potential new crops. Halophytes have been tested as vegetable, forage, and oilseed crops in agronomic field trials. The most productive species yield 10 to 20 ton/ha of biomass on seawater irrigation, equivalent to conventional crops. The oilseed halophyte, Salicornia bigelovii, yields 2 t/ha of seed containing 28% oil and 31% protein, similar to soybean yield and seed quality. Halophytes grown on seawater require a leaching fraction to control soil salts, but at lower salinities they outperform conventional crops in yield and water use efficiency. Halophyte forage and seed products can replace conventional ingredients in animal feeding systems, with some restrictions on their use due to high salt content and antinutritional compounds present in some species. Halophytes have applications in recycling saline agricultural wastewater and reclaiming salt-affected soil in arid-zone irrigation districts.
• Glenn, E. P., Cohen, M. J., Morrison, J. I., Valdés-Casillas, C., & Fitzsimmons, K. (1999). Science and policy dilemmas in the management of agricultural waste waters: The case of the Salton Sea, CA, USA. Environmental Science and Policy, 2(4-5), 413-423.
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  Abstract: The Salton Sea in California, a repository for agricultural drainage water and sewage effluent from the United States and Mexico, is increasing in salinity and may soon be too saline to support fish and other elements of the present food chain. Massive fish kills and bird die-offs in recent years have led to a perception that this is an ecosystem in trouble, and an initiative to restore the Salton Sea is underway. Engineering proposals to stabilize the salinity and volume of the Salton Sea could cost a billion dollars or more to install and ten million dollars per year or more to operate, and could adversely affect adjacent ecosystems, with no certainty that the problems of the sea would be remedied. On the other hand, allowing salinity to increase will likely lead to a dramatic change in the species composition of the sea over the next two decades. We consider the possible ecological consequences of allowing salinity to increase in the Salton Sea to levels similar to other salt lakes in the region. We also consider the possible adverse ecological affects of engineering proposals which would discharge contaminated Salton Sea water into the Gulf of California or divert excess Colorado River water that now flows to the Colorado River delta to the Salton Sea. We consider the benefits of an alternative proposal, which would handle the problem within the Salton Basin by installing designed wildlife habitats around the Sea while allowing the main body to become hypersaline. We recommend a set of principles which should guide policy decisions regarding restoration of the Salton Sea. © Elsevier Science Ltd.
• Glenn, E. P., Garcia, J., Tanner, R., Congdon, C., & Luecke, D. (1999). Status of wetlands supported by agricultural drainage water in the Colorado River Delta, Mexico. HortScience, 34(1), 39-45.
• Glenn, E. P., Moore, D., Akutagawa, M., Himler, A., Walsh, T., & Nelson, S. G. (1999). Correlation between Gracilaria parvispora (Rhodophyta) biomass production and water quality factors on a tropical reef in Hawaii. Aquaculture, 178(3-4), 323-331.
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  Abstract: The factors controlling the growth of the edible, red seaweed, Gracilaria parvispora Abbott (long ogo), on the south reef of Molokai, HI, were investigated to determine where productive new plantings could he located. Experiments were conducted in October, 1997, and March and June, 1998, in which G. parvispora biomass production was correlated with water quality factors measured at six sites over each 21-day experiment. Water motion, temperature, salinity, nitrate and phosphate varied among sites and experiments, but were not significantly (P > 0.05) correlated with growth. A strong correlation, however, was found between biomass production and ammonia concentration (r = 0.91, P < 0.001). Ammonia levels ranged from 0.2-4.0 mmol m-3 over sites and experiments but were skewed towards low values, as was biomass production. The transient nature of ammonia distribution on this reef explains the patchy distribution of locations at which G. parvispora is productive, noticed in previous experiments. Large-scale Gracilaria culture on such a reef would require adding an external source of fertilizer, which may disrupt the reef ecology. An alternative is to develop a dispersed form of cultivation at sites that receive ammonia enrichment from the land, in which case the crop can help absorb excess nutrients entering the reef.
• Lash, D. W., Glenn, E. P., Waugh, W. J., & Baumgartner, D. J. (1999). Effects of grazing exclusion and reseeding on a former uranium mill site in the Great Basin desert, Arizona. Arid Soil Research and Rehabilitation, 13(3), 253-264.
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  Abstract: Germinable seed in the soil seed bank and vegetation were characterized at a former uranium mill site in the Great Basin desert, Arizona, 10 years after a remediation program was conducted to remove surface contamination and revegetate the site. The objective of the study was to evaluate the effectiveness of reseeding as routinely practiced to revegetate such sites. Three different conditions at the site were evaluated: (1) an area that had been bladed to remove topsoil then reseeded with exotic and native species and fenced to exclude livestock (ungrazed-bladed-reseeded) (2) a control area inside the fence that had not been bladed or reseeded (ungrazed), and (3) for further comparison, an area outside the fence that was undisturbed by the milling and remediation efforts but has received normal grazing pressure (grazed). Each condition was represented by three plots, from which soil samples and transect data were collected. The diversity of species and total number of viable seeds in the seed bank (top 5 cm of soil) were lowest in the ungrazed-bladed-reseeded plots (P < 0.05). These plots also had lower plant cover (15%) than the ungrazed plots (24%) (P < 0.05), comparable to the cover on grazed plots (11%), even after 10 years of grazing exclusion. We conclude that at this site the results of topsoil removal and replacement were not effectively remediated by reseeding. Although these methods may be effective in register climates, more intensive efforts to reintroduce vegetation may be required in desert sites such as this.
• Tanner, R., Glenn, E. P., & Moore, D. (1999). Food chain organisms in hypersaline, industrial evaporation ponds. Water Environment Research, 71(4), 494-505.
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  Abstract: Evaporation ponds are becoming widely used by industry and agriculture for the disposal of brines as a result of increasingly strict regulations pertaining to off-site disposal methods. Migratory waterfowl and other wildlife can become reliant on such ponds, which can present biological hazards depending on the chemicals they receive. This study examined the algae, invertebrates, and chemistry of two large, hypersaline, industrial wastewater ponds near Phoenix, Arizona, at which waterfowl die-offs (primarily cared grebes, Podiceps nigricollis) were reported. The objectives were to determine what attracted birds to the ponds and whether the ponds were directly responsible for bird deaths. High levels of total salts and nitrate were detected in both ponds, but selenium (16 to 41 μg/L) was the only potentially toxic element that reached levels of concern in the water column. Dominant algae were diatoms, Chaetoceros sp. and Nitzschia frustrulum (Kurtz.) Grun. (up to 6.5 x 105 cells/mL), and cyanobacteria, Synechococcus Nageli 1849 (up to 8.8 x 106 cells/mL). These are normal components of hypersaline ponds and natural salt lakes. However, Chaetoceros levels were negatively correlated with salinity levels in the ponds and a species turnover is expected as ponds age. Primary aquatic fauna were Artemia franciscana (brine shrimp), a filter feeder that consumes algae, and Trichocorixa sp. (waterboatman), a carnivorous insect that presumably feeds on brine shrimp. Brine shrimp were the primary attractant of birds; they were harvested by numerous resident and migratory waterfowl. Selenium levels in brine shrimp (2 to 10 mg/kg) were above recommended levels for food chain organisms in aquatic ecosystems but were well below levels that can cause acute toxicity. Brine shrimp fed to zebra danios fish (Brachydanio refio) in a bioassay were nontoxic. As at other locations where grebe mortality events have been reported in recent years, the cause of death of birds visiting these evaporation ponds is unknown. Therefore, it is concluded that these ponds may not be directly toxic to visiting wildlife, but that evaporation ponds such as these are attractants for wildlife and may pose a long-term hazard through the accumulation of selenium in the food chain. Zero- discharge evaporation ponds may be useful as an interim solution to the brine disposal problem but do not represent a safe, permanent solution.
• Fitzsimmons, K., Lovely, C., & Glenn, E. (1998). Growth differences among widely separated geographic accessions of fourwing saltbush (Atriplex canescens) in the great basin desert, New mexico, USA. Arid Soil Research and Rehabilitation, 12(2), 87-94.
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  Abstract: As part of a revegetation project, 16 accessions representing five varieties of Atriplex canescens (Pursch.) Nutt. were grown in a common garden experiment in northwestern New Mexico. The accessions were collected from Sonora, Mexico, to Idaho and from near sea level to 2800-m elevation. Plants were grown for 16 months on native sail irrigated with saline water (4800-9400 mg L-1) collected from a seepage intercept system surrounding the ash disposal ponds at a coal-fired power plant, at 1660-m elevation. All but var. grandidentatum from Mexico had high survival, but there was a fourfold variation in the amount of net growth among accessions. The northern accessions had 50% greater net growth than the southern accessions. Revegetation projects that utilize A. canescens need to match the seed source to the local site conditions. Saline water recovered from the leach fraction below power plant ash ponds can be used to establish stands of A. canescens for revegetation projects.
• Glenn, E. P., & Brown, J. J. (1998). Effects of soil salt levels on the growth and water use efficiency of Atriplex canescens (Chenopodiaceae) varieties in drying soil. American Journal of Botany, 85(1), 10-16.
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  PMID: 21684874;Abstract: The effect of salt stress on the growth and water use efficiency of the xerohalophyte Atriplex canescens (Pursh.) Nutt. in drying soil was determined by growing plants to the wilting point in soils receiving a one-time irrigation of nutrient solution containing low, medium, and high levels of NaCl. The experiment compared three varieties of A. canescens that differed in salt tolerance and capacity for Na and K uptake in previous research. Contrary to expectations, we did not find that water and salt stress were strictly additive in reducing plant performance. Soil salts enhanced the growth performance of the plants in drying soil by increasing their days to wilting, ability to extract water from the soil, organic matter production, and water use efficiency. The variety with the highest salt tolerance also had the highest growth rates and water use efficiency on drying soils. We conclude that tolerances to water and salt stress are linked through a common mechanism of Na uptake for osmotic adjustment in this species.
• Glenn, E. P., Moore, D., Brown, J. J., Tanner, R., Fitzsimmons, K., Akutigawa, M., & Napolean, S. (1998). A sustainable culture system for Gracilaria parvispora (Rhodophyta) using sporelings, reef growout and floating cages in Hawaii. Aquaculture, 165(3-4), 221-232.
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  Abstract: A culture system for the edible, red seaweed, Gracilaria parvispora Abbott (long ogo), was developed in Hawaii that utilized a hatchery to produce tetrasporophyte and gametophyte life stages of the seaweed, reef growout of sporelings to harvest size adults, and multiplication of the harvested thalli in floating cages prior to sale. A central cooperative operated the hatchery and floating cages, and marketed the product. Sporelings from the hatchery were distributed to coastal residents who established patches of seaweed on the reef and sold their harvest to the cooperative. Mean relative growth rate of seaweed in the cages over 52 weeks was 2.64% d-1 and productivity was 14.8 g m-2 d-1 (dry weight), within the range of intensive culture systems. Cage cultures were not sensitive to water motion over the range of 4-14 cm s-1 but growth and productivity tended to be higher in summer and spring than in winter. The culture system potentially overcomes problems that have hindered development of a sustainable supply of this species: low availability of wild stocks due to overharvesting; low productivity of spore cultures; and deterioration of vegetative cultures over time. Some of the elements may be applicable to other areas where wild stocks of Gracilaria have been overharvested.
• Glenn, E., Moore, D., Sanderson, S., Brown, J. J., Lash, D., Nelson, M., & Waugh, J. (1998). Comparison of growth and morphology of Atriplex canescens varieties Occidentalis and Angustifolia. Southwestern Naturalist, 43(2), 176-182.
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  Abstract: Two varieties of Atriplex canescens from a disturbed site in the Navajoan desert of the Colorado Plateau were compared. Variety angustifolia could be distinguished from van occidentalis by its greater fruit diameter (>1.5 cm) and leaf width:length ratio (>10), and absence of 6-methoxy flavonols in the leaves. Variety angustifolia was the less common variety on the site but was clearly superior to van occidentalis in growth and water use efficiency of seedlings in a greenhouse study. Seedlings of both varieties were transplanted into caliche and dune soil at the site; growth and survival were followed over the establishment year. Variety angustifolia had 3 to 6 times greater canopy volume than van occidentalis on both soil types, but the differences were greatest on dune soil, in which van occidentalis had only 32% survival and showed little growth whereas van angustifolia had nearly complete survival and positive growth over the establishment year. The results support other studies suggesting the diploid van angustifolia is adapted to rapid establishment on unstable dune soils, whereas the slower-growing van occidentalis may be adapted for heavier soils which retain moisture longer than dune sand. Variety angustifolia was the better choice of germplasm for revegetation of this disturbed site.
• Glenn, E., Smith, M. S., & Squires, V. (1998). On our failure to control desertification: Implications for global change issues, and a research agenda for the future. Environmental Science and Policy, 1(2), 71-78.
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  Abstract: Desertification has been recognized as a major environmental problem for more than 20 years. Control of desertification has been the subject of many international efforts; it has been a major focus of UNEP and there is a UN Convention to Combat Desertification. Despite this, control of desertification is considered by many observers to have been a failure. This paper reviews the history of formalized efforts to combat desertification, looks at the lessons that should be learned, and identifies opportunities for establishing closer links between desertification and other aspects of global change research. These include integrating biophysical and social science disciplines, the use of a hierarchical approach to research and monitoring, the development of functional classifications of landscapes and social systems, and the implementation of specific studies on key representative transects across the world. Progress towards repairing this form of land degradation will depend upon developing economic links between desertification and other global environmental problems.
• Glenn, E., Tanner, R., Mendez, S., Kehret, T., Moore, D., Garcia, J., & Valdes, C. (1998). Growth rates, salt tolerance and water use characteristics of native and invasive riparian plants from the delta of the Colorado River, Mexico. Journal of Arid Environments, 40(3), 281-294.
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  Abstract: Six riparian plant species representing native and invasive species from the Colorado River delta in the Sonoran Desert of Mexico were tested for salt tolerance and water use characteristics in a greenhouse study in Tucson, Arizona. Negative linear regression equations relating relative growth rates (RGR, g g-1 day-1) of each species to mean root zone salinity had high coefficients of determination (r2 = 0.73-0.86, p < 0.001). Salt tolerance levels, expressed as % reduction in RGR per g l-1 NaCl in soil solution, varied widely among species: Allenrolfea occidentalis, 0% reduction; Tamarix ramosissima, 1.8% reduction; Pluchea sericea, 3.5% reduction; and Baccharis salicifolia, Salix gooddingii and Populus fremontii, 7-9% reduction (p < 0.05). Transpiration was proportional to RGR for all species. Contrary to some previous reports, Tamarix did not have unusually high water use compared to the other species. Differences in salt tolerance among species determined in this study support field observations that soil salinity, which can reach high values along channelized and flow-regulated stretches of south-western United States rivers due to lack of overbank flooding, is a major factor in the replacement of native riparian species by invasive species.
• Glenn, E., Tanner, R., Miyamoto, S., Fitzsimmons, K., & Boyer, J. (1998). Water use, productivity and forage quality of the halophyte Atriplex nummularia grown on saline waste water in a desert environment. Journal of Arid Environments, 38(1), 45-62.
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  Abstract: The halophyte Atriplex nummularia Lindl. was grown in a desert climate in Tempe, AZ, for 3 years in outdoor drainage lysimeters. Plants were irrigated with two sources of waste water from an electric power plant: mildly saline (1149 mgl-1 total dissolved solids (TDS)) storm runoff collected in a pond, or brackish (4100 mgl-1 TDS) blowdown water from cooling towers. Plants were irrigated weekly with enough water to replace evapo-transpiration losses but leaching fractions were only 4-10%. Atriplex nummularia performed equally well on both water sources, even though soil solution salinity in the rooting depth profile ranged from 300-1000 mol m-3 NaCl in lysimeters irrigated with blowdown water compared to only 40-90 mol m-3 in lysimeters irrigated with pond water. Atriplex nummularia had higher productivity, water use efficiency and consumptive water use than conventional forage crops in Arizona irrigation districts. Nutritional content of plant tissues was acceptable for use as a ruminant forage. Atriplex nummularia had key traits desired in a plant for disposal of saline water: high consumptive use to minimize land area devoted to reuse; high salt tolerance, conferring the ability to grow under low leaching fraction to minimize discharge to the aquifer; and useful production.
• Glenn, E., Miyamoto, S., Moore, D., Brown, J. J., Thompson, T. L., & Brown, P. (1997). Water requirements for cultivating Salicornia bigelovii Torr. with seawater on sand in a coastal desert environment. Journal of Arid Environments, 36(4), 711-730.
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  Abstract: The forage and oilseed halophyte, Salicornia bigelovii Torr., was grown in gravity-drained lysimeters set in open plots of the same crop over two seasons in a coastal desert environment in Sonora, Mexico. The lysimeters were irrigated daily with seawater (40 g l-1 salts) at rates ranging from 46-225% of potential evaporation. Biomass and seed yields increased with increasing irrigation depth over the range of treatment. Biomass yields ranged from 13.6-23.1 t DM ha-1, equivalent to conventional forage crops, on seasonal water application depths of 2.3-3.8 m, but were markedly lower at lower irrigation depths. Increasing the irrigation depth lowered the soil solution salinity, resulting in greater growth and water use, and hence leaching fractions that were nearly even over irrigation treatments, averaging 0.5. Evapo-transpiration rose in direct proportion to the irrigation depth. Potential evaporation was estimated by site pan evaporation and by the Blaney-Criddle and Penman models using climatological data; the methods agreed within 15%. The ratio of evapo-transpiration to potential evaporation increased over the growing season and approached 1.5 by pan on the highest irrigation treatment due to the combined effects of high transpiration and high evaporation from the permanently moist soil surface. The best field predictor of biomass yield was the salinity of the soil moisture in the top 15 cm of soil profile, which constitutes that root zone for this crop. Root zone salinity must be kept at 70-75 g l-1 for high yields. Although irrigation and drainage requirements were high compared to conventional crops, seawater irrigation appears to be feasible in medium sand and could augment crop production along coastal deserts. The possibility of using this crop for animal production is discussed.
• Riley, J. J., Fitzsimmons, K. M., & Glenn, E. P. (1997). Halophyte irrigation: An overlooked strategy for management of membrane filtration concentrate. Desalination, 110(3), 197-211.
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  Abstract: It is argued that the preferred paradigm for utilizing membrane filtration concentrate conceptually, and legally in Arizona, is to view it as an agricultural water management opportunity rather than a wastewater disposal problem. Halophyte farms irrigated with concentrate at a 5% leaching rate are projected to be productive for over 100 y in southern Arizona without affecting the quality of the underlying groundwater any more than conventional agriculture. The authors recommend that halophyte irrigation be included in the management options for membrane filtration concentrate at current and future sites.
• Glenn, E. P., Lee, C., Feiger, R., & Zengel, S. (1996). Effects of water management on the wetlands of the Colorado River delta, Mexico. Conservation Biology, 10(4), 1175-1186.
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  Abstract: The lower delta of the Colorado River has been severely affected by the upstream diversion of water for human use. No river water is officially appropriated to support delta wetlands, yet large marsh areas of conservation interest still exist below the agricultural fields in Mexico. These are supported by flood water, agricultural drainage water, municipal sewage effluent, and seawater in the intertidal zone. From 1973 to 1993 the area of freshwater and brackish marsh varied widely, from 5800 to 63,000 ha. A new opportunity exists to restore wetlands in the delta now that the upstream water impoundments on the Colorado River are filled and flood flows are once again directed to the delta. But flood control structures now channel most of the flood water directly to the sea, and most of the effluent waters are deposited in evaporation basins rather than used to support wetlands. If the Yuma Desalting Plant in the United States becomes operational and if the Rio Hardy wetlands continue to be drained, the area of brackish wetlands could decrease to less than 2000 ha in near future. Preserving the remaining wetlands will require a binational water management plan. The plan should maximize the benefits to wetlands of flood and irrigation return flows that enter the delta, and it should minimize flood risks.
• Glenn, E. P., Moore, D., Fitzsimmons, K., & Azevedo, C. (1996). Spore culture of the edible red seaweed, Gracilaria parvispora (Rhodophyta). Aquaculture, 142(1-2), 59-74.
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  Abstract: A hatchery was established for the inoculation of coral chips, pebbles and lines with carpospores of Gracilaria parvispora, an edible market seaweed in Hawaii. Cystocarpic thalli were placed over various substrates in tanks of aerated seawater. Carpospores attached readily to substrates and after 72 h in hatchery tanks, mean spore density on slides placed in hatch tanks was 1800 cm-2. Inoculated coral chips and pebbles were placed out in a seawater pond. After 18-22 weeks spore density declined to 4 cm-2 but 61% of substrates still had plants. Only 36% of inoculated lines developed good growth, but growth was more rapid on lines than on pebble or chips. Lines yielded two crops per year, each approximately 800 g m-2 (fresh weight), whereas chips and pebbles required 50 weeks growth for an equivalent harvest. Tetrasporophytes were the dominant adult stage but cystocarpic plants accounted for approximately 10% of the culture products, demonstrating that the life cycle of this species was completed within the culture system. Spore culture of Gracilaria allowed mass production of plants on a variety of artificial substrates but the disadvantages included the long lag period and the lower reliability compared with vegetative production methods.
• Glenn, E., Pfister, R., Brown, J. J., Thompson, T. L., & O'Leary, J. (1996). Na and K accumulation and salt tolerance of Atriplex canescens (Chenopodiaceae) genotypes. American Journal of Botany, 83(8), 997-1005.
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  Abstract: Sixteen accessions of the xerohalophyte, Atriplex canescens (Pursh.) Nutt., differing in tendency to accumulate Na or K in leaf tissues, were compared for salt tolerance in a greenhouse study. Plants were grown along a salinity gradient from 72 to 2017 mol/m3 NaC1 measured in the root zone. Growth rates (RGR) were negatively affected by salinity for all accessions. Initial leaf levels of Na (measured before exposing plants to saline solutions) were positively correlated with subsequent RGR's of accessions on the salinity gradient (r = 0.60-0.88, P < 0.05 across salinity levels), whereas initial leaf K levels were negatively correlated (r = -0.68 to -0.85, P < 0.01 across salinity levels). Varieties linearis (S. Wats.) Munz and grandidentatum Stutz and Sanderson had greater tendency for Na accumulation, lower tendency for K, and higher growth rates on saline solutions than var occidentalis (Torr. and Frem.) Welsh and Stutz accessions. Within var occidentalis accessions, RGRs were negatively correlated with initial leaf levels of K but not Na. Postexposure leaf Na and K levels were not strongly correlated with RGR's. All accessions responded to salinity by increasing their uptake of Na, which is the primary mechanism of osmotic adjustment to salinity in this species. It is suggested that differences in tendency to accumulate Na or K among A. canescens genotypes are related to their specialization for saline or xeric hahitats, respectively.
• Khan, M. J., & Glenn, E. P. (1996). Yield and evapotranspiration of two barley varieties as affected by sodium chloride salinity and leaching fraction in lysimeter tanks. Communications in Soil Science and Plant Analysis, 27(1-2), 157-177.
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  Abstract: Two barley varieties (California Mariout and Gustoe), differing in putative salt tolerance, were grown in lysimeter tanks containing 1 m3 of sandy loam soil in a greenhouse experiment in Tucson, Arizona. The varieties were subjected to three salinity treatments (0, 150, and 250 mol/m3 NaCl) and two leaching fractions (LF) (0.2 and 0.4). Mariout, a reportedly salt-tolerant, high straw variety, yielded more grain and biomass than the semi-dwarf variety, Gustoe, across salinity treatments, but slopes of growth responses to salinity were similar. Mariout grain yields on control solution were the equivalent of 4.8-5.3 t/ha, similar to good open field yields of this variety. Gustoe yields were lower, 3.5-4.1 t/ha. Salinity reduced Mariout yields to 4 t/ha on 150 mol/m3 and this was judged to be the highest irrigation salinity which will produce economic yields of this variety. The saturated soil extract (ECe) in the root zone at this salinity was 11.8 dS/m. For both varieties, biomass and grain yields were reduced by 2.4-3.1% for each 1 dS/m increase in ECe, and ECe's producing 50% yield reduction of biomass or grain ranged from 17-21 dS/m. Increasing the LF increased biomass and grain production by both varieties, especially on 150 mol/m3 treatment, but did not reduce ECe as much as expected. Adding additional water as a LF increased the amount of evapotranspiration rather than reducing ECe. Copyright © 1996 by Marcel Dekker, Inc.
• Miyamoto, S., Glenn, E. P., & Olsen, M. W. (1996). Growth, water use and salt uptake of four halophytes irrigated with highly saline water. Journal of Arid Environments, 32(2), 141-159.
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  Abstract: Halophytes have been considered as potential crops for irrigated production with brackish water or seawater. This study was conducted to obtain quantitative information on salt tolerance, water use and salt uptake responses of four halophytes: A triplex nummularia Lindl., Distichlis palmeri Fassett, Batis maritima L., and Suaeda esteroa Ferron & Whitmore. Outdoor lysimeter experiments were conducted during the summer of 1991 and again during the spring of 1992 in the subtropic coastal desert of Sonora, Mexico. The plants were grown at an average leaching fraction of approximately 0.3 with diluted or concentrated seawater having salinity levels of 1-2, 10, 20, 40, and 60 g 1-1. Results indicate that these halophyte species can be grown productively at a leaching fraction of 0.30 or less when salinity of the irrigation water is less than 10 g 1-1. At higher salinities, frequent irrigation at higher leaching fractions may be required for these species. © 1996 Academic Press Limited.
• Olsen, M. W., Frye, R. J., & Glenn, E. P. (1996). Effect of salinity and plant species on CO₂ flux and leaching of dissolved organic carbon during decomposition of plant residue. Plant and Soil, 179(2), 183-188.
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  Abstract: Mitigation of increased concentrations of CO2 in the atmosphere by plants may be more efficient in saline systems with soils lower in organic matter than in other freshwater systems. In saline systems, decomposition rates may be lower and potential soil carbon storage higher than in fresh water systems. The effects of salinity, plant species and time on CO2 surface flax and dissolved organic carbon (DOC) leached during irrigation were determined in the laboratory in microcosms containing sand amended with residues of two halophytes, Atriplex nummularia and Salicornia bigelovii, and one glycophyte, Triticum aestivum. Surface flux of CO2 and DOC leached during decomposition were monitored for 133 days at 24 °C in microcosms containing different plant residue (5% w/w). Microcosms were irrigated every 14 days with distilled water or seawater adjusted to 10, 20, or 40 g L-1 salts. CO2 flux and DOC leached were significantly higher from microcosms amended with A. nummularia residue compared to S. bigelovii or T. aestivum at all salinities and decreased significantly over time for all plant species. Irrigating with water of high salinity, 40 g L-1, compared to distilled water resulted in a decrease in CO2 surface flux and DOC in leachate, but differences were not significant at all sampling dates. Results indicate that plant residue composition, as well as increased salinity, affect CO2 surface flux and DOC in leachate during plant residue decomposition and may be an important consideration for C storage in saline systems.
• Swingle, R. S., Glenn, E. P., & Squires, V. (1996). Growth performance of lambs fed mixed diets containing halophyte ingredients. Animal Feed Science and Technology, 63(1-4), 137-148.
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  Abstract: The growth rates of lambs fed on diets containing halophyte components were assessed in two trials of 84days duration each, from weaning to slaughter weight. Three halophyte forages, Atriplex barclayana, Suaeda esteroa and Salicornia bigelovii straw, were compared with Cynodon dactylon hay at 30% of the diet. Halophyte forages were much higher in mineral content than Cynodon hay (24-34% vs. 5%). The trials also compared Salicornia seed meal with cottonseed meal at 10% inclusion. All diets were high in concentrate (70%) and contained 12.5-15% protein. Dry matter intake was higher for lambs fed diets containing halophyte forages than for lambs fed on the grass control diet. Because of the increased intake, halophyte-fed lambs were able to gain at the same rate as the control lambs, but, as expected, feed efficiency was lower and water intake was higher. Carcass merit of all lambs was excellent and was not affected by the inclusion of halophyte forages in the diet. In one trial an additional control treatment was included in which Cynodon hay was supplemented with NaCl to attempt to isolate the effect of excess salt on feed intake and growth. However, the simulated halophyte diet (Cynodon + NaCl) supported lower weight gains and intake rates than the control or natural halophyte diets, showing that the form in which salts are present in halophyte forages is important to their acceptability to animals. It is concluded that halophytes could become important feed resources at moderate inclusion levels wherever production of these plants can be justified agronomically.
• Zengel, S. A., & Glenn, E. P. (1996). Presence of the endangered desert pupfish (Cyprinodon macularius, cyprinidontidae) in Cienega de Santa Clara, Mexico, following an extensive marsh dry-down. Southwestern Naturalist, 41(1), 73-78.
• Glenn, E., Thompson, T., Frye, R., Riley, J., & Baumgartner, D. (1995). Effects of salinity on growth and evapotranspiration of Typha domingensis Pers.. Aquatic Botany, 52(1-2), 75-91.
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  Abstract: The interactions between salinity, growth and evapotranspiration (Et) were investigated for Typha domingensis Pers. in a greenhouse growth experiment and in Cienega de Santa Clara, a coastal desert marsh in the Colorado River delta in Mexico. Although Typha is often found in brackish as well as fresh water marshes, salinity imposed severe constraints to its growth and distribution. In the 68 day greenhouse experiment, growth was maximal at 1.1 ppt. (control solution), half-maximal at 3.5 ppt. and negligible above 6 ppt.; 75% mortality occurred at 15 ppt. Et decreased with salinity in proportion to growth reduction. In the Cienega, T. domingensis was only found in water of 5-8 ppt. or less. When inflow water was 1.0 ppt., Typha Et was estimated to be 1.3 times pan evaporation (Eo), whereas when inflow water was 3.2 ppt., estimated Et Eo was only 0.7. An estimated half of the inflow water to the Cienega exited the vegetated portion of the Cienega unused, owing to the salt tolerance limit of Typha. A practical objective of the study was to predict the effect of brine placement from the Yuma Desalting Plant into the Cienega; it was concluded that the resulting inflow salinity of 7-10 ppt. would result in deterioration of the Typha stands owing to excess salinity. © 1995.
• Zengel, S. A., Meretsky, V. J., Glenn, E. P., Felger, R. S., & Ortiz, D. (1995). Cienega de Santa Clara, a remnant wetland in the Rio Colorado delta (Mexico): vegetation distribution and the effects of water flow reduction. Ecological Engineering, 4(1), 19-36.
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  Abstract: The Cienega de Santa Clara is the largest remaining wetland in the Rio Colorado delta; it supports endangered bird and fish species. The Cienega is maintained by agricultural drainage water discharge from the USA which in the future may be diverted to the Yuma Desalting Plant. We examined the existing vegetation patterns and effects of flow disruption on vegetation using seasonal aerial and ground surveys. The Cienega was dominated by Typha domingensis and contained eight subdominant hydrophytes in addtition. The distribution of marsh plants was related to salinity and water depth within the Cienega. Disturbance in the form of burning of the Typha and grazing of cattle on the new growth had a marked effect on the status of the vegetation in accessible parts of the marsh. During 8 months of unplanned flow interruption due to the need for canal repairs, 60-70% of the marsh foliage died back. Green vegetation was confined to a low-lying geologic fault which retained water; however, Typha domingensis regenerated from dormant rhizomes following the return of canal flow. Though the vegetation proved resilient, prolonged flow reduction would unavoidably reduce the size of the wetland and its capacity to support associated wetland functions. © 1995.
• Glenn, E. P., Olsen, M., Frye, R., Moore, D., & Miyamoto, S. (1994). How much sodium accumulation is necessary for salt tolerance in subspecies of the halophyte Atriplex canescens?. Plant, Cell and Environment, 17(6), 711-719.
• Thompson, T. L., & Glenn, E. P. (1994). Plaster standards to measure water motion. Limnology and Oceanography, 39(7), 1768-1779.
• Glenn, E., Squires, V., Olsen, M., & Frye, R. (1993). Potential for carbon sequestration in the drylands. Water, Air, & Soil Pollution, 70(1-4), 341-355.
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  Abstract: Non-forested drylands occupy 43% of the world's land surface yet they are not currently regarded as important in sequestering carbon due to overuse and poor management. Seventy percent of drylands have already undergone moderate to severe desertification and an additional 3.5% drops out of economic production each year. Reversing the trend towards desertification through cultivation of halophytes on saline lands, revegetation of degraded rangelands and other innovative conservation measures could result in net C sequestration in dryland soils of 0.5-1.0 Gt yr-1 at a cost of $10-18 t-1 C, based on a 100 yr scenario. Investment in antidesertification measures in the world's drylands appears to be an economical method to mitigate CO2 buildup in the atmosphere while accomplishing a major international objective of restoring dryland productivity. © 1993 Kluwer Academic Publishers.
• Hodges, C. N., Thompson, T. L., Riley, J. J., & Glenn, E. P. (1993). Reversing the flow: Water and nutrients from the sea to the land. Ambio, 22(7), 483-490.
• Ojima, D. S., Dirks, B. O., Glenn, E. P., Owensby, C. E., & Scurlock, J. O. (1993). Assessment of C budget for grasslands and drylands of the world. Water, Air, & Soil Pollution, 70(1-4), 95-109.
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  Abstract: Intergovernmental Panel on Climate Change (IPCC) estimates indicate that potential changes in seasonal rainfall and temperature patterns in central North America and the African Sahel will have a greater impact on biological response (such as plant production and biogeochemical cycling) and feedback to climate than changes in the overall amount of annual rainfall. Simulation of grassland and dryland ecosystem responses to climate and CO2 changes demonstrates the sensitivity of plant productivity and soil C storage to projected changes in precipitation, temperature and atmospheric CO2. Using three different land cover projections, changes in C levels in the grassland and dryland regions from 1800 to 1990 were estimated to be -13.2, -25.5 and -14.7 Pg, i.e., a net source of C due to land cover removal resulting from cropland conversion. Projections into the future based on a double-CO2 climate including climate-driven shifts in biome areas by the year 2040 resulted in a net sink of +5.6, +27.4 and +26.8 Pg, respectively, based upon sustainable grassland management. The increase in C storage resulted mainly from an increase in area for the warm grassland sub-biome, together with increased soil organic matter. Preliminary modeling estimates of soil C losses due to 50 yr of regressive land management in these grassland and dryland ecoregions result in a 11 Pg loss relative to current conditions, and a potential loss of 37 Pg during a 50 yr period relative to sustainable land-use practices, an average source of 0.7 Pg C yr-1. Estimates of the cost of a 20 yr rehabilitation program are 5 to 8×109 US$ yr-1, for a C sequestering cost of approximately 10 US$ per tC. © 1993 Kluwer Academic Publishers.
• Pielke, R. A., Lee, T. J., Glenn, E. P., & Avissar, R. (1993). Influence of halophyte plantings in arid regions on local atmospheric structure. International Journal of Biometeorology, 37(2), 96-100.
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  Abstract: The practicality of modifying climate in arid regions through irrigation has up to now been constrained by the availability of fresh water with which to grow crops. The present results suggest a new paradigm: the use of salt water to grow halophyte crops and modify local climate along coastal deserts and other arid regions where saline water supplies are available. © 1993 International Society of Biometeorology.
• Glenn, E. P., & Doty, M. S. (1992). Water motion affects the growth rates of Kappaphycus alvarezii and related red seaweeds. Aquaculture, 108(3-4), 233-246.
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  Abstract: Tagged thalli of three Eucheumatoid seaweed species were grown in five locations comprising a natural gradient of water motion on a reef flat in Kaneohe Bay, Oahu. The gradient of water motion was related to the wind-shadow effect of a small island on the reef which sheltered part of the reef from the prevailing trade winds. Three experiments were conducted at different times of year in which growth rates, water motion, and other environmental factors were measured weekly in the pens for 8 to 12 weeks. In all three experiments significant (P < 0.05) correlations were found between the growth rates of the seaweeds and the amount of water motion measured by the dissolution rate of calcium sulfate clodcards placed in the pens. Regression equations of growth rates vs. water motion were significant for all experiments at P < 0.05 but the slopes of the equations differed among the different seaweed species, for the same species at different times of year, and for the same species attached loosely or rigidly to the substratum. The growth response of Kappaphycus alvarezii to water motion was greater than the responses of K. striatum or Eucheuma denticulatum. With K. alvarezii, growth response to water motion was greater in summer than winter, and in thalli that were loosely held to the substratum vs. thalli that were held rigidly. Coefficients of determination indicated that water motion could account for 81-98% of the variation in growth rates among pens in the different experiments. Growth rates increased up to the highest water motion velocities measured in the pens, 15 cm s-1. It was concluded that culture of these species requires high levels of water motion provided by strong and consistent trade winds under reef farming conditions. The results support the multifactorial hypothesis of seaweed growth regulation. © 1992.
• Glenn, E. P., Coates, W. E., Riley, J. J., Kuehl, R. O., & Swingle, R. S. (1992). Salicornia bigelovii Torr.: a seawater-irrigated forage for goats. Animal Feed Science and Technology, 40(1), 21-30.
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  Abstract: Dry biomass of the halophyte Salicornia bigelovii was substituted for rhodesgrass as the forage component (approx. 50% as consumed) of diets fed to Damascus kid goats in the United Arab Emirates. Because of the high NaCl content of the biomass it was tested in two forms designed to bring the NaCl content within acceptable levels. In one treatment it was presented in a 1:1 (w/w) mixture with rhodesgrass to dilute the NaCl content. In the second treatment the S. bigelovii biomass was washed in seawater, pressed and redried to reduce the NaCl content; it was presented as the sole forage component in that treatment. The washing procedure reduced the NaCl content of the S. bigelovii biomass by approximately half, from 23-30% to 8-13%, but also removed cell solubles. There were no significant differences (P < 0.05) among diet treatments in weight gains of animals, which ranged from 63 to 90 g day-1 for males and 50 to 57 g day-1 for females. Goats consumed significantly (P < 0.01) more washed S. bigelovii biomass than either rhodesgrass or unwashed S. bigelovii/rhodesgrass mixture. They also required significantly (P < 0.05) more feed per unit of weight gain on that treatment which was attributed to the lowered protein content and partial loss of cell solubles of washed S. bigelovii biomass. Differences in water consumption among treatments were non-significant. It was concluded that S. bigelovii biomass is an acceptable substitute for rhodesgrass in coastal arid zones where fresh water for forage production is limited but where saline water resources can be exploited. © 1992.
• Glenn, E. P., Felger, R. S., Burquez, A., & Turner, D. S. (1992). Cienega de Santa Clara: endangered wetland in the Colorado River delta, Sonora, Mexico. Natural Resources Journal, 32(4), 817-824.
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  Abstract: The Cienega de Santa Clara, is undergoing alterations due to operation of the Yuma Desalting Plant in the USA. This is the largest remaining wetland in the delta region, containing rare and endangered species including desert pupfish Cyprinodon macularius and Yuma clapper rail Rallus longirostris yumanensis, yet no official consideration has been given to the effect of the altered conditions on the wetland flora and fauna. -from Authors
• Glenn, E. P., Pitelka, L. F., & Olsen, M. W. (1992). The use of halophytes to sequester carbon. Water, Air, & Soil Pollution, 64(1-2), 251-263.
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  Abstract: Wild salt tolerant plants, halophytes, could be grown on 130×106 ha of potentially arable land in the world's coastal deserts, inland salt deserts and areas of secondary salinization in irrigation districts. Halophytes have potential as biomass crops to directly sequester up to 0.7 Gt C, similar to tree plantations, or they can play an indirect role in absorbing C from the atmosphere by providing food, fodder and energy crops from a new land base. To the extent new cropland can be developed from unused saline land, further land clearing and loss of C storage in forest fallow and old growth forests can be spared, thereby adding to the carbon sequestering potential of all usable ecosystems. © 1992 Kluwer Academic Publishers.
• Glenn, E. P., O'Leary, J. W., Watson, M. C., Thompson, T. L., & Kuehl, R. O. (1991). Salicornia bigelovii Torr.: An oilseed halophyte for seawater irrigation. Science, 251(4997), 1065-1067.
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  PMID: 17802093;Abstract: The terrestrial halophyte, Salicornia bigelovii Torr., was evaluated as an oilseed crop for direct seawater irrigation during 6 years of field trials in an extreme coastal desert environment. Yields of seed and biomass equaled or exceeded freshwater oilseed crops such as soybean and sunflower. The seed contained 26 to 33 percent oil, 31 percent protein, and was low in fiber and ash (5 to 7 percent). The oil and meal were extracted by normal milling equipment, and the oil was high in linoleic acid (73 to 75 percent) and could replace soybean oil in chicken diets. The meal had antigrowth factors, attributed to saponins, but could replace soybean meal in chicken diets amended with the saponin antagonist, cholesterol. Salicornia bigelovii appears to be a potentially valuable new oilseed crop for subtropical coastal deserts.
• Glenn, E. P., & Doty, M. S. (1990). Growth of the seaweeds Kappaphycus alvarezii, K. striatum and Eucheuma denticulatum as affected by environment in Hawaii. Aquaculture, 84(3-4), 245-255.
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  Abstract: Three commercial gel-producing seaweed species native to the Philippines were grown experimentally in pens on an algal reef-flat in Kaneohe Bay, Oahu, Hawaii. Growth rates and environmental conditions were measured for 55 consecutive weeks. The normal northeast trade winds created a flow of water through the 272-m2 farm, one side of which faced northeast. Upstream thalli of Kappaphycus alvarezii grew at an average relative growth rate of 5.06%/day, whereas K. striatum and Eucheuma denticulatum grew at 3.50%/day. These growth rates and the overall productivity of 20.8 tonnes dry wt/ha per year were similar to those obtained on Philippine reef-flat farms. Growth rates tended to be independent of season, and correlations between growth rates and environmental variables were low. The study suggested a range of conditions under which these eucheumatoids can be productive in a farm setting: temperature maxima of 24-30°C and minima of 21-22°C; nitrogen levels of 2-4 μ-atm/l; phosphate levels of 0.5-1.0 μ-atm/l; and high solar energy levels. The pH and salinity were near 8.0 and 32 ppt, respectively, throughout the study period. The degree of water motion per se was not correlated with growth rate but the direction of wind across the farm was important. Downstream thalli generally appeared unhealhy and grew at half the rate of upstream thalli. When the normal trade winds reversed, the (formerly) upstream thalli grew poorly. None of the measured environmental factors was correlated with the downstream growth reduction, and its cause remains unknown. © 1990.
• Glenn, E. P., Smith, C. M., & Doty, M. S. (1990). Influence of antecedent water temperatures on standing crop of a Sargassum spp.-dominated reef flat in Hawaii. Marine Biology, 105(2), 323-328.
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  Abstract: The standing crop of seaweeds was estimated monthly over a 22 mo period from 1971 to 1973 on a reef at Waikiki, Honolulu, Hawaii. Wet and dry standing crops averaged 1.2 and 0.26 kg m-2, respectively. Approximately 70% of the total biomass was contributed by a single species, Sargassum polyphyllum, and the remainder was contributed by 29 other species. The size of the total standing crop and of S. polyphyllum in particular was highly correlated with antecedent water temperatures. The highest correlation was with temperatures recorded 3 to 4 wk prior to the estimate of standing crop. Approximately 65% of the variability of the standing crop on the reef was explained by this single variable. Multiple linear-regression analyses did not uncover further significant environmental factors related to the S. polyphyllum standing crop. Temperature may have acted by stimulating the vegetative growth of new plants between the period of minimal abundance in February and maximal abundance in October. The population decline after November relates to the switch to reproductive growth. Total productivity on the reef was estimated to be 16 800 to 19 314 kg dry wt ha-1 yr-1, based on the average size of the standing crop and estimates of removal rate and turnover time, respectively. © 1990 Springer-Verlag.
• Glenn, E. P., & O'Leary, J. (1985). Productivity and irrigation requirements of halophytes grown with seawater in the Sonoran Desert.. Journal of Arid Environments, 9(1), 81-91.
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  Abstract: Native and exotic halophytes (Atriplex, Salicornia, Distichlis, Cressa and Batis) were grown in field trials at Puerto Penasco, Sonora, Mexico using hypersaline (40per mille) seawater for irrigation. The most productive halophyte species yielded 1364-1794 g dry weight m-2 yr-1. The minimum effective water rate was 18 m yr-1, using undiluted seawater and the flood method of application. Using 10per mille artificial seawater and the sprinkler method of application, Salicornia bigelovii yielded >1000 g DW m-2 with only 2.4 m of water. Atriplex plants were 12-17% protein but ash content was also high. -from Authors
• O'Leary, J., Glenn, E. P., & Watson, M. C. (1985). Agricultural production of halophytes irrigated with seawater. Plant and Soil, 89(1-3), 311-321.
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  Abstract: Growing agricultural crops with direct seawater irrigation has progressed within the past few years from the conceptual to the experimental phase. This has been accomplished by selecting halophytes with inherently high salinity tolerance for use as crop plants rather than by increasing the ability of traditional crop plants to tolerate seawater. Some of the halophytes being investigated for use as crops in seawater irrigation scenarios have high nutritional value as forage or fodder crops. Most of them also have high digestibility. The limiting factor in such use is their high salt content, but this limitation can be moderated. However, since seeds of halophytes do not accumulate salt any more than do those of glycophytes, the greatest promise for seawater-irrigated halophytes probably will be as seed crops. The seeds of many halophytes have high protein and oil contents and compare favorably with traditional oilseed crops. Sustained high yields of seed and biomass already have been obtained from some halophytes irrigated with seawater, and within the next few years seawater agriculture should proceed from the experimental to the operational phase. © 1985 Martinus Nijhoff Publishers.
• Glenn, E. P. (1984). Seasonal effects of radiation and temperature on growth of greenhouse lettuce in a high insolation desert environment. Scientia Horticulturae, 22(1-2), 9-21.
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  Abstract: 'Ostinata', 'Summer Bibb' and 'Grand Rapids' lettuce were measured for seasonal growth in a greenhouse in a high-insolation desert environment. Growth of all 3 cultivars was positively correlated with radiation up to the highest level measured, 550 cal cm-2 day-1. Crops grown in the autumn used light 2-3 times more efficiently than crops grown in spring. Daytime air temperatures were also positively correlated with growth, and there was a significant temperature × radiation interaction. The best predictor of growth was the product of day temperature and the log of radiation. This variable explained much of the difference between the growth of autumn and spring crops. Autumn crops were grown under higher temperatures and thus responded more steeply to radiation than spring crops. High temperatures during the summer rainy season were associated with bolting. A general curve to predict the length of the crop cycle from radiation data alone was constructed from data for Tucson, Arizona, U.S.A., crops and data from the literature for lettuce grown in Great Britain and the Great Lakes region of the United States. © 1984.
• Glenn, E. P., Cardran, P., & Thompson, T. (1984). Seasonal effects of shading on growth of greenhouse lettuce and spinach. Scientia Horticulturae, 24(3-4), 231-239.
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  Abstract: Lettuce (cultivar 'Summer Bibb') and spinach ('Melody') were grown under various shade treatments in a greenhouse at Tucson, Arizona, U.S.A. Six experiments were conducted with lettuce and five with spinach at different times of the year. The objective was to compare their growth potentials over a wide range of PAR from natural sunlight. Lettuce responded positively to PAR up to the highest level measured, 45 mol m-2 day-1. The maximum growth rate was 0.221 g g-1 day-1 from Day 14 to Day 42 after seeding. Spinach was PAR-saturated at approximately 25 mol m-2 day-1 and the maximum growth rate was 0.194 g g-1 day-1. The PAR compensation point for growth was less than 1 mol m-2 day-1 for both plants, but neither produced market-quality heads below 8 mol m-2 day-1 due to etiolation effects. The ground cover of a plant per unit dry weight increased at low PAR levels, and spinach had a 4-fold greater ground cover per unit weight than lettuce at all PAR levels. Growth curves were analyzed by means of double reciprocal equations. Coefficients of determination (r2) were greater than 0.96 in all individual experiments. Pooled lettuce and spinach data had r2 values of 0.747 and 0.846, respectively. The equations of best fit had similar y-intercepts for both plants, but the slope of the spinach equation was significantly greater than that of the lettuce equation, denoting a lower response to PAR for spinach. Lettuce was more efficient than spinach in PAR utilization. Both plants grew well under high PAR conditions, however, and it was concluded that high insolation desert regions of the world can be used for greenhouse production of lettuce and spinach. © 1984.
• Glenn, E. P., & Doty, M. S. (1981). Photosynthesis and respiration of the tropical red seaweeds, Eucheuma striatum (Tambalang and elkhorn varieties) and E. denticulatum. Aquatic Botany, 10(C), 353-364.
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  Abstract: Rates of photosynthesis for three Central Pacific forms of Eucheuma (Tambalang and Elkhorn varieties of E. striatum Schmitz, and E. denticulatum (Burm.) Collins & Hervey) ranged from 2031-2685 μl O2 h-1 g-1 dry wt. tissue under the conditions used when measured by manometric techniques in the laboratory (24°C, 1600 ft-candles light). Respiration ranged from 471-630 μl O2 h-1 g-1 dry wt. Photosynthesis and respiration of Tambalang showed diurnal variations and also varied with the position of the tissue along a branch. Light saturation of photosynthesis (24°C) occurred at 1200 ft-candles for all three forms. Inhibition by light intensity for Tambalang was 18% at 5000 ft-candles compared to the rate at 1000 ft-candles, which was measured in air by the infrared gas analyzer technique. The photosynthetic capacity of Tambalang was found to decrease with increasing water depth, at a site in Kaneohe Bay, Hawaii. Maximum rates of photosynthesis for all three forms occurred at 30°C with Q10 values of ca. 3.0 between 20 and 30°C at 1600 ft-candles of illumination. Inhibition of photosynthesis occurred above 32°C. The response of respiration to temperature showed two peaks of activity air at 25% C and 1000 ft-candles illumination by the infrared gas analyzer. Tambalang had a carbon dioxide compensation point of 29-32 ppm when measured in recirculated air at 25°C and 1000 ft-candles illumination by the infrared gas analyzer technique. © 1981.
• Hodges, C. N., Fontes, M. R., Glenn, E. P., Katzen, S., & Colvin, L. B. (1981). Seawater-based agriculture as a food production defense against climate variability.. Food-climate interactions. Proc. workshop, Berlin, 1980, 81-99.
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  Abstract: A limiting factor for food production in sunny, productive regions is the scarcity of fresh water. Also, many irrigated soils become saline. Reviews the use of seawater to increase agricultural production and reduce climate vulnerability by adapting conventional crops to salt tolerance, by using seawater for environmental control, by culturing aquatic animals, and, in the work described in detail, by domesticating wild halophytes-plants which have evolved in hypersaline conditions-for livestock feed. Halophytes irrigated exclusively with seawater equalled or surpassed alfalfa in yield and protein, excess salts were removed by leaching, and initial animal trials were promising. -Authors