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At least 523 records · Page 29Linked to original sources
USGS1987

Industrial, agricultural, and petroleum contaminants in cormorants wintering near the Houston Ship Channel, Texas, USA

Double-crested cormorants (Phalacrocorax auritus ) collected in the Houston Ship Channel, Texas, USA, in November shortly after their fall migration contained residues of several industrial, agricultural, and petroleum contaminants including polychlorinated styrenes (PCS's), polychlorinated biphenyls (PCB's), DDE, and petroleum hydrocarbons. PCS concentrations in over-wintering birds collected in late February were three times higher than those in birds collected in November. PCB and petroleum concentrations remained at about the same level throughout the 3-month winter period. Petroleum hydrocarbons were present in all cormorants and residues in some individuals exceeded 25 ppm (wet weight). Mean DDE residues in samples collected in November and February were less than 1 ppm. Low concentrations of five other organochlorine compounds, not detected in cormorants collected in November, were recovered in birds collected in February.

Texas↗
USGS2016

Effects of hydrology, watershed size, and agricultural practices on sediment yields in two river basins in Iowa and Mississippi

The specific sediment yield (SSY) from watersheds is the result of the balance between natural, scale-dependent erosion and deposition processes, but can be greatly altered by human activities. In general, the SSY decreases along the course of a river as sediments are trapped in alluvial plains and other sinks. However, this relation between SSY and basin area can actually be an increasing one when there is a predominance of channel erosion relative to hillslope erosion. The US Geological Survey (USGS) conducted a study of suspended sediment in the Iowa River basin (IRB), Iowa, and the Yazoo River basin (YRB), Mississippi, from 2006 through 2008. Within each river basin, the SSY from four largely agricultural watersheds of various sizes (2.3 to 35,000 km 2 [0.9 to 13,513 mi 2 ]) was investigated. In the smallest watersheds, YRB sites had greater SSY compared to IRB sites due to higher rain erosivity, more erodible soils, more overland flow, and fluvial geomorphological differences. Watersheds in the YRB showed a steady decrease in SSY with increasing drainage basin area, whereas in the IRB, the maximum SSY occurred at the 30 to 500 km 2 (11.6 to 193 mi 2 ) scale. Subsurface tile drainage and limits to channel downcutting restrict the upstream migration of sediment sources in the IRB. Nevertheless, by comparing the SSY-basin size scaling relationships with estimated rates of field erosion under conservation and conventional tillage treatments reported in previous literature, we show evidence that the SSY-basin size relationship in both the IRB and YRB remain impacted by historical erosion rates that occurred prior to conservation efforts.

Iowa, Mississippi↗
USGS2018

Testing a two-scale focused conservation strategy for reducing phosphorus and sediment loads from agricultural watersheds

This study tested a focused strategy for reducing phosphorus (P) and sediment loads in agricultural streams. The strategy involved selecting small watersheds identified as likely to respond relatively quickly, and then focusing conservation practices on high-contributing fields within those watersheds. Two 5,000 ha (12,360 ac) watersheds in the Driftless Area of south central Wisconsin, previously ranked in the top 6% of similarly sized Wisconsin watersheds for expected responsiveness to conservation efforts to reduce high P and sediment loads, were chosen for the study. The stream outlets from both watersheds were monitored from October of 2006 through September of 2016 for streamflow and concentrations of sediment, total P, and, beginning in October of 2009, total dissolved P. Fields and pastures having the highest potential P delivery to the streams in each watershed were identified using the Wisconsin P Index (Good et al. 2012). After three years of baseline monitoring (2006 to 2009), farmers implemented both field- and farm-based conservation practices in one watershed (treatment) as a means to reduce sediment and P inputs to the stream from the highest contributing areas, whereas there were no out-of-the-ordinary conservation efforts in the second watershed (control). Implementation occurred primarily in 2011 and 2012. In the four years following implementation of conservation practices (2013 through 2016), there was a statistically significant reduction in storm-event suspended sediment loads in the treatment watershed compared to the control watershed when the ground was not frozen ( p = 0.047). While there was an apparent reduction in year-round suspended sediment event loads, it was not statistically significant at the 95% confidence level ( p = 0.15). Total P loads were significantly reduced for runoff events ( p < 0.01) with a median reduction of 50%. Total P and total dissolved P concentrations for low-flow conditions were also significantly reduced ( p < 0.01) compared to the control watershed. This study demonstrated that a strategy that first identifies watersheds likely to respond to conservation efforts and then focuses implementation on relatively high-contributing fields within those watersheds can be successful in reducing stream P concentrations and loads.

Wisconsin↗
USGS2020

Assessing water-quality changes in agricultural drainages: Examples from oxbow lake tributaries in Mississippi, USA and simulation-based power analyses

Hydrology and water quality (suspended sediment, total nitrogen, ammonia, total Kjeldahl nitrogen, nitrate plus nitrite, and total phosphorus (TP)) were monitored in two small agricultural drainages in northwestern Mississippi to document changes in water quality that coincided with the implementation of BMPs in upstream drainages. Using an event-based dataset and bootstrapping techniques, we tested for difference and equivalence in median event concentration and differences in concentration-discharge (C-Q) relationships between an early and late period at each site, where most of the major BMP implementation occurred during the early period. Results for one site were inconclusive. None of the constituents had statistically different or equivalent event concentrations between the periods, indicating a lack of evidence to tell whether water quality had changed or stayed the same, and only TP had a significantly higher C-Q slope during the late period. At the other site, more than half the constituents had a significantly different median, slope, or intercept between periods, indicating a 35% or more decrease in event concentration following a period of intense BMP implementation. These mixed results could be due to variety of differences between the sites including BMP implementation, production practices, and crops. We also used the monitoring data to generate synthetic data and perform a simulation-based power analysis to explore the ability to detect change under 25 scenarios of sampled event counts and hypothetical percent changes. The simulation-based power analysis indicated that high natural variability in event concentration and flow hindered our ability to detect change. Based on our monitoring, data analysis, and power analysis, we provide recommendations for future monitoring.

Mississippi↗
USGS1977

A selected bibliography: Remote sensing applications in agriculture

The bibliography contains nearly 300 citations of selected publications and technical reports dealing with the application of remote-sensing techniques to the collection and analysis of agricultural information. Most of the items included were published between January 1968 and December 1975, although some earlier works of continuing interest are included.

Report↗
USGS1993

Occurrence and transport of agricultural chemicals in the Mississippi River basin, July through August 1993

Heavy rainfall and severe flooding in the upper Mississippi River Basin from mid-June through early August 1993 flushed extraordinarily large amounts of agricultural chemicals (herbicides and nitrate) into the Mississippi River, many of its tributaries, and, ultimately, the Gulf of Mexico. Even though extremely high streamflows were recorded during the flood in 1993, concentrations of herbicides, such as atrazine, alachlor, cyanazine, and metolachlor, were similar to the maximum concentrations measured during spring and summer 1991 and 1992. It was anticipated that the higher streamflows during the flood would dilute the concentrations of herbicides that are usually flushed into streams in late spring and summer. Instead, concentrations were similar to those measured during much lower flows, but the daily loads of herbicides transported in some reaches of the Mississippi River were higher than those measured in 1991 and 1992. The total atrazine load transported to the Gulf of Mexico from April through August 1993 (539,000 kilograms) was about 80 percent higher than that for the same period in 1991 and 235 percent higher than for the same period in 1992. The concentrations of atrazine and cyanazine in a few individual samples exceeded health-based limits for drinking water. However, because drinking-water regulations are based on the average of at least four quarterly samples, the annual average concentrations in the Mississippi River probably will not exceed these limits for 1993. Nitrate concentrations were similar to those measured during spring and summer 1991 and 1992. The loads of nitrate-nitrogen transported into the Gulf of Mexico during July and August 1993 were as much as 5,734 metric tons per day. These loads generally are similar to those measured in spring 1991 and 1992 but larger than those measured in summer 1991 and 1992. The total nitrate-nitrogen load transported to the Gulf of Mexico from April through August 1993 (827,000 metric tons) was about 37 percent larger than that for this same period in 1991 and 112 percent larger than that for the same period in 1992. The transport of extraordinarily high loads of nitrate and large amounts of fresh-water into the Gulf of Mexico during midsummer when primary production is highest could increase phytoplankton biomass and affect the gulf ecosystem along the Louisiana coast.

Mississippi River↗
USGS2013

Electron donor concentrations in sediments and sediment properties at the agricultural chemicals team research site near New Providence, Iowa, 2006-07

The concentrations of electron donors in aquifer sediments are important to the understanding of the fate and transport of redox-sensitive constituents in groundwater, such as nitrate. For a study by the U.S. Geological Survey National Water-Quality Assessment Program, 50 sediment samples were collected from below the water table from 11 boreholes at the U.S. Geological Survey Agricultural Chemicals Team research site near New Providence, Iowa, during 2006-07. All samples were analyzed for gravel, sand (coarse, medium, and fine), silt, clay, Munsell soil color, inorganic carbon content, and for the following electron donors: organic carbon, ferrous iron, and inorganic sulfide. A subset of 14 sediment samples also was analyzed for organic sulfur, but all of these samples had concentrations less than the method detection limit; therefore, the presence of this potential electron donor was not considered further. X-ray diffraction analyses provided important semi-quantitative information of well-crystallized dominant minerals within the sediments that might be contributing electron donors.

Iowa↗
USGS2014

Occurrence of pesticides in groundwater and sediments and mineralogy of sediments and grain coatings underlying the Rutgers Agricultural Research and Extension Center, Upper Deerfield, New Jersey, 2007

Water and sediment samples were collected from June through October 2007 from seven plots at the Rutgers Agricultural Research and Extension Center in Upper Deerfield, New Jersey, and analyzed for a suite of pesticides (including fungicides) and other physical and chemical parameters (including sediment mineralogy) by the U.S. Geological Survey. Plots were selected for inclusion in this study on the basis of the crops grown and the pesticides used. Forty-one pesticides were detected in 14 water samples; these include 5 fungicides, 13 herbicides, 1 insecticide, and 22 pesticide degradates. The following pesticides and pesticide degradates were detected in 50 percent or more of the groundwater samples: 1-amide-4-hydroxy-chorothalonil, alachlor sulfonic acid, metolachlor oxanilic acid, metolachlor sulfonic acid, metalaxyl, and simazine. Dissolved-pesticide concentrations ranged from below their instrumental limit of detection to 36 micrograms per liter (for metolachlor sulfonic acid, a degradate of the herbicide metolachlor). The total number of pesticides found in groundwater samples ranged from 0 to 29. Fourteen pesticides were detected in sediment samples from continuous cores collected within each of the seven sampled plots; these include 4 fungicides, 2 herbicides, and 7 pesticide degradates. Pesticide concentrations in sediment samples ranged from below their instrumental limit of detection to 34.2 nanograms per gram (for azoxystrobin). The total number of pesticides found in sediment samples ranged from 0 to 8. Quantitative whole-rock and grain-coating mineralogy of sediment samples were determined by x-ray diffraction. Whole-rock analysis indicated that sediments were predominantly composed of quartz. The materials coating the quartz grains were removed to allow quantification of the trace mineral phases present.

New Jersey↗
USGS2014

Pharmaceutical compounds in shallow groundwater in non-agricultural areas of Minnesota: study design, methods, and data, 2013

The U.S. Geological Survey, in cooperation with the Minnesota Pollution Control Agency, completed a study on the occurrence of pharmaceutical compounds and other contaminants of emerging concern in shallow groundwater in non-agricultural areas of Minnesota during 2013. This report describes the study design and methods for the study on the occurrence of pharmaceuticals and other contaminants of emerging concern, and presents the data collected on pharmaceutical compounds. Samples were analyzed by the U.S. Geological Survey National Water Quality Laboratory for 110 pharmaceutical compounds using research method 9017. Samples from 21 of 45 wells had detectable concentrations of at least one of the 110 compounds analyzed. One sample contained detectable concentrations of nine compounds, which was the most detected in a single sample. Fewer than five compounds were detected in most samples. Among all samples, 27 of the 110 compounds were detected in groundwater from at least one well. Desmethyldiltiazem and nicotine were the most frequently detected compounds, each detected in 5 of 46 environmental samples (one well was sampled twice so a total of 46 environmental samples were collected from 45 wells). Caffeine had the highest detectable concentration of all the compounds at 2,060 nanograms per liter.

Minnesota↗
USGS2024

Where is the water? Agriculture [poster]

Description Water is an integral part of how we interact with the environment and live our everyday lives. This educational poster illustrates agricultural water use, how water moves, and different ways that water is used both naturally and through human interaction. This poster is intended for eighth-grade audiences and younger.

General Information Product↗
USGS2001

Shallow ground-water quality in an agricultural area of the lower coastal plain of South Carolina, 1997

Ground-water-quality samples were collected from 30 shallow monitoring wells located in agricultural areas of the lower Coastal Plain of South Carolina during the summer of 1997 as part of the U.S. Geological Survey National Water-Quality Assessment Program in the Santee River Basin and Coastal Drainages study unit. The wells were completed in sand to clayey sand sediments of the surficial aquifer and sampled one time for selected field properties, and nutrient, major ion, and pesticide concentrations. This report contains the results of the sampling effort.

South Carolina↗
USGS2004

Quaternary stratigraphy and tectonics, and late prehistoric agriculture of the Safford Basin (Gila and San Simon river valleys), Graham County, Arizona

This guidebook accompanied the 46th annual meeting of the Rocky Mountain Cell of the Friends of the Pleistocene (FOP) and the 2002 Fall Field Trip of the Arizona Geological Society. The meeting and field trip were held in the Safford Basin, southeastern Arizona. The Friends of the Pleistocene is an informal gathering of Quaternary geologists, geomorphologists, and pedologists who meet annually for a field conference. The first part of the guidebook consists of road logs with descriptions of stops covering the three days of the field trip. An overview of the geology of the Safford Basin is given in Stop 1-1. The second part of the guidebook consists of four short papers that discuss adjacent areas or that expand upon the road log descriptions of the field trip stops. The first paper by Reid and Buffler is a summary of upper Cenozoic depositional facies in the Duncan Basin, the first basin to the east of the Safford Basin. The next three papers expand upon (1) the soil study of the gridded field agricultural complex (Stop 2-3, Homburg and Sandor), (2) the vertebrate fossils of the San Simon Valley in the southeastern part of the Safford Basin (Stop 3-1, Thrasher), and (3) paleoIndian irrigation systems and settlements in Lefthand Canyon at the foot of the Pinaleno Mountains (Stop 3-2, Neely and Homburg).

Open-File Report↗
USGS2005

Water-quality data from two agricultural drainage basins in northwestern Indiana and northeastern Illinois: I. Lagrangian and synoptic data, 1999-2002

Methods of data collection and results of analyses are presented for Lagrangian and synoptic water-quality data collected from two agricultural drainages, the Iroquois River in northwestern Indiana and Sugar Creek in northwestern Indiana and northeastern Illinois. During six separate sampling trips, in April, June and September 1999, May 2000, September 2001 and April 2002, 152 discrete water samples were collected to characterize the water chemistry over the course of 2 to 4 days on each of these drainages. Data were collected for nutrients, major inorganic constituents, dissolved organic carbon, trace elements, dissolved gases, total bacterial cell counts, chlorophyll- a concentrations, and suspended sediment concentrations. In addition, field measurements of streamflow, pH, specific conductance, water temperature, and dissolved oxygen concentration were made during all trips except April 1999.

Indiana, Illinois↗
USGS2005

Evaluation of unsaturated-zone solute-transport models for studies of agricultural chemicals

Seven unsaturated-zone solute-transport models were tested with two data sets to select models for use by the Agricultural Chemical Team of the U.S. Geological Survey's National Water-Quality Assessment Program. The data sets were from a bromide tracer test near Merced, California, and an atrazine study in the White River Basin, Indiana. In this study the models are designated either as complex or simple based on the water flux algorithm. The complex models, HYDRUS2D, LEACHP, RZWQM, and VS2DT, use Richards' equation to simulate water flux and are well suited to process understanding. The simple models, CALF, GLEAMS, and PRZM, use a tipping-bucket algorithm and are more amenable to extrapolation because they require fewer input parameters. The purpose of this report is not to endorse a particular model, but to describe useful features, potential capabilities, and possible limitations that emerged from working with the model input data sets. More rigorous assessment of model applicability involves proper calibration, which was beyond the scope of this study. Uncalibrated ("cold") simulations were run using all seven models to predict the transport of bromide (Merced) and the transport and fate of atrazine and three of its transformation products (White River Basin). Among the complex models, HYDRUS2D successfully predicted both the surface retention and accumulation of bromide at depth at the Merced site, whereas RZWQM and VS2DT predicted only the latter. RZWQM predictions of atrazine were closest to observed values at the White River Basin site, where preferential flow has been observed. LEACHP predicted smaller solute concentrations than observed at both the Merced and White River Basin sites. Among the simple models, CALF predicted the highest values of atrazine and deethylatrazine at the measurement depth of 1.5 meters. CALF includes the Addiscott flow option for preferential flow, and also accepts user-specified dispersivity. PRZM underpredicted solute concentrations, probably because control of dispersion is a problem with this model. GLEAMS has a maximum simulation depth of 1.5 meters, which is limiting for mass-balance purposes because it creates a potential disconnect between unsaturated-zone transport and the water table. Of the models tested, RZWQM, HYDRUS2D, VS2DT, GLEAMS and PRZM had graphical user interfaces. Extensive documentation was available for RZWQM, HYDRUS2D, and VS2DT. RZWQM can explicitly simulate water and solute flux in macropores, and both HYDRUS2D and VS2DT can simulate water and solute flux in two dimensions. The version of RZWQM tested had a maximum simulation depth of 3 meters. The complex models simulate the formation, transport, and fate of degradates of up to three to five compounds including the parent, with the exception of VS2DT, which simulates the transport and fate of a single compound.

California, Indiana↗
USGS2006

Application of municipal biosolids to dry-land wheat fields - A monitoring program near Deer Trail, Colorado (USA). A presentation for an international conference: "The Future of Agriculture: Science, Stewardship, and Sustainability", August 7-9, 2006, Sacramento, CA

Since late 1993, Metro Wastewater Reclamation District of Denver (Metro District), a large wastewater treatment plant in Denver, Colorado, has applied Grade I, Class B biosolids to about 52,000 acres of non-irrigated farmland and rangeland near Deer Trail, Colorado. In cooperation with the Metro District in 1993, the U.S. Geological Survey (USGS) began monitoring ground water at part of this site. In 1999, the USGS began a more comprehensive study of the entire site to address stakeholder concerns about the chemical effects of biosolids applications. This more comprehensive monitoring program has recently been extended through 2010. Monitoring components of the more comprehensive study included biosolids collected at the wastewater treatment plant, soil, crops, dust, alluvial and bedrock ground water, and stream bed sediment. Streams at the site are dry most of the year, so samples of stream bed sediment deposited after rain were used to indicate surface-water effects. This presentation will only address biosolids, soil, and crops. More information about these and the other monitoring components are presented in the literature (e.g., Yager and others, 2004a, b, c, d) and at the USGS Web site for the Deer Trail area studies at http://co.water.usgs.gov/projects/CO406/CO406.html. Priority parameters identified by the stakeholders for all monitoring components, included the total concentrations of nine trace elements (arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc), plutonium isotopes, and gross alpha and beta activity, regulated by Colorado for biosolids to be used as an agricultural soil amendment. Nitrogen and chromium also were priority parameters for ground water and sediment components. In general, the objective of each component of the study was to determine whether concentrations of priority parameters (1) were higher than regulatory limits, (2) were increasing with time, or (3) were significantly higher in biosolids-applied areas than in a similar farmed area where biosolids were not applied. Where sufficient samples could be collected, statistical methods were used to evaluate effects. Rigorous quality assurance was included in all aspects of the study. The roles of hydrology and geology also were considered in the design, data collection, and interpretation phases of the study. Study results indicate that the chemistry of the biosolids from the Denver plant was consistent during 1999-2005, and total concentrations of regulated trace elements were consistently lower than the regulatory limits. Plutonium isotopes were not detected in the biosolids. Leach tests using deionized water to simulate natural precipitation indicate arsenic, molybdenum, and nickel were the most soluble priority parameters in the biosolids. Study results show no significant difference in concentrations of priority parameters between biosolids-applied soils and unamended soils where no biosolids were applied. However, biosolids were applied only twice during 1999-2003. The next soil sampling is not scheduled until 2010. To date concentrations of most of the priority parameters were not much greater in the biosolids than in natural soil from the sites. Therefore, many more biosolids applications would need to occur before biosolids effects on the soil priority constituents can be quantified. Leach tests using deionized water to simulate precipitation indicate that molybdenum and selenium were the priority parameters that were most soluble in both biosolids-applied soil and natural or unamended soil. Study results do not indicate significant differences in concentrations of priority parameters between crops grown in biosolids-applied areas and crops grown where no biosolids were applied. However, crops were grown only twice during 1999-2003, so only two crop samples could be collected. The wheat-grain elemental data collected during 1999-2003 for both biosolids-applied areas and unamended areas are similar

Open-File Report↗
USGS2008

Chemical and microbiological water quality of subsurface agricultural drains during a field trial of liquid dairy manure effluent application rate and varying tillage practices, Upper Tiffin Watershed, southeastern Michigan

A field trial was done in the Upper Tiffin River Watershed, in southeastern Michigan, to determine the influence of liquid dairy manure effluent (LDME) management practices on the quality of agricultural subsurface-drain water. Samples from subsurface drains were analyzed for nutrients, fecal-coliform and Escherichia coli ( E. coli ) bacteria, antibiotics, chemicals typically detected in wastewater, and the occurrence of genes indicating the presence of shiga-toxin-producing E. coli , or of bovine-specific Bacteroidetes bacteria. Samples were collected from November 2, 2006, to March 20, 2007, from eight subsurface drains under field plots that received no LDME and no tillage (controls) or received 4,000 or 8,000 gallons per acre (gal/acre) of LDME and either no tillage or two different types of tillage. The two types of tillage tested were (1) ground-driven, rotary, subsurface cultivation and (2) rolling-tine aeration. Samples were collected before LDME application and at 4 hours, and 1, 2, 6, 7, and 14 days post-application. Nutrient concentrations were high in subsurface-drain water throughout the field-trial period and could not be attributed to the field-trial LDME application. Of the 59 drain-water samples, including those collected before LDME application and control samples for each date, 56 had concentrations greater than the U.S. Environmental Protection Agency (USEPA), Ecoregion VI recommended surface-water criterion for total phosphorus, and all samples had concentrations greater than the recommended total nitrogen criterion. Nitrate + nitrite nitrogen concentration exceeded 20 milligrams per liter for every sample and contributed most to the total nitrogen concentrations. Substantial increases in drain-water concentrations of organic and ammonia nitrogen and total phosphorus were found for all treatments, including controls, at 14 days post-application after 0.84 inch of rainfall over 2 days. E. coli concentrations exceeded the USEPA recreational-water-quality single-sample criterion of 235 colony forming units per 100 milliliters in only 3 of 56 samples. Of these three samples, two were collected within 1 day post-LDME application from the treatment receiving 8,000 gal/acre LDME with no tillage (NT8000). The third sample was from the rolling-tine aerator treatment with 4,000 gal/acre LDME application rate after the first significant rainfall. Two wastewater chemicals and two bacterial genes ( eae A and stx 1) detected in the LDME, but absent in field blank or pre-application samples, were detected in the 4-hour or 1-day postapplication NT8000 samples. No LDME-associated chemicals were detected in later samples from the NT8000 treatment, and none were detected in samples from other treatments after the first significant rainfall. Results of this field trial were somewhat equivocal with respect to the influence of LDME concentration and tillage practices on subsurface-drain water quality, both immediately after LDME application and in the longer term, after significant rainfall. Interpretation of study findings is limited by the fact that treatments were not replicated, and flow rate or discharge from the subsurface drains was not measured. Nevertheless, study results provide useful information about nutrient and bacteria concentrations in subsurface drains during the non-growing season. In addition, study results demonstrate some potential for the use of chemical and microbiological indicators of LDME transport to subsurface drains.

Michigan↗
USGS2008

Year 3 summary report: Baseline selenium monitoring of agricultural drains operated by the Imperial Irrigation District in the Salton Sea Basin

This report summarizes findings from the third year of a 4-year-long field investigation to document selected baseline environmental conditions in 29 agricultural drains and ponds operated by the Imperial Irrigation District along the southern border of the Salton Sea. Routine water quality and fish species were measured at roughly quarterly intervals from April 2007 to January 2008. The water quality measurements included total suspended solids and total (particulate plus dissolved) selenium. In addition, during April and October 2007, water samples were collected from seven intensively monitored drains for measurement of particulate and dissolved selenium, including inorganic and organic fractions. In addition, sediment, aquatic food chain matrices (particulate organic detritus, filamentous algae, net plankton, and midge [chironomid] larvae), and two fish species (western mosquitofish, Gambusia affinis ; and sailfin molly, Poecilia latipinna ) were sampled from the seven drains for measurement of total selenium concentrations. The mosquitofish and mollies were intended to serve as surrogates for desert pupfish ( Cyprinodon macularius ), an endangered species that we were not permitted to take for selenium determinations. Water quality values were typical of surface waters in a hot desert climate. A few drains exhibited brackish, near anoxic conditions especially during the summer and fall when water temperatures occasionally exceeded 30°C. In general, total selenium concentrations in water varied directly with conductivity and inversely with pH. Although desert pupfish were found in several drains, sometimes in relatively high numbers, the fish faunas of most drains and ponds were dominated by nonnative species, especially red shiner ( Cyprinella lutrensis ), mosquitofish, and mollies. Dissolved selenium in water samples from the seven intensively monitored drains ranged from 0.700 to 24.1 µg/L, with selenate as the major constituent in all samples. Selenium concentrations in other matrices varied widely among drains and ponds, with at least one drain (for example, Trifolium 18) exhibiting especially high concentrations in food chain organisms (in detritus, 13.3–28.9 µg Se/g; in net plankton, 11.9–19.3 µg Se/g; in midge larvae, 12.7–15.4 µg Se/g) and fish (in mollies, 12.8-25.1 µg Se/g; in mosquitofish, 13.2-20.2 µg Se/g; all concentrations are dry weights). These elevated concentrations approached or exceeded average concentrations reported from flowing waters in seleniferous wetlands in the San Joaquin Valley.

California↗