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USGS2008

Near-decadal changes in nitrate and pesticide concentrations in the South Platte River alluvial aquifer, 1993-2004

The lower South Platte River basin of Colorado and Nebraska is an area of intense agriculture supported by surface-water diversions from the river and ground-water pumping from a valley-fill alluvial aquifer. Two well networks consisting of 45 wells installed in the South Platte alluvial aquifer were sampled in the early 1990s and again in the early 2000s to examine near-decadal ground-water quality changes in irrigated agricultural areas. Ground-water age generally increases and dissolved-oxygen content decreases with distance along flow paths and with depdi below the water table, and denitrification is an important natural mitigation mechanism for nitrate in downgradient areas. Ground-water travel time from upland areas to the river ranges from 12 to 31 yr on the basis of apparent ground-water ages. Ground-water nitrate concentrations for agricultural land-use wells increased significantly for oxidized samples over the decade, and nitrogen isotope ratios for oxidized samples indicate synthetic fertilizer as the predominant nitrate source. Ground-water concentrations of atrazine, DEA, and prometon decreased significandy. The decrease in pesticide concentrations and a significant increase in the ratio of DEA to atrazine suggest decreases in pesticide concentrations are likely caused by local decreases in application rates and/or degradation processes and that atrazine degradation is promoted by oxidizing conditions. The difference between results for oxidizing and nitrate-reducing conditions indicates redox state is an important variable to consider when evaluating ground-water quality trends for redox-sensitive constituents such as nitrate and pesticides in the South Platte alluvial aquifer. Copyright ?? 2008 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.

Journal of Environmental Quality↗

USGS2017

Similarities and differences in occurrence and temporal fluctuations in glyphosate and atrazine in small Midwestern streams (USA) during the 2013 growing season

Glyphosate and atrazine are the most intensively used herbicides in the United States. Although there is abundant spatial and temporal information on atrazine occurrence at regional scales, there are far fewer data for glyphosate, and studies that compare the two herbicides are rare. We investigated temporal patterns in glyphosate and atrazine concentrations measured weekly during the 2013 growing season in 100 small streams in the Midwestern United States. Glyphosate was detected in 44% of samples (method reporting level 0.2 μg/L); atrazine was detected above a threshold of 0.2 μg/L in 54% of samples. Glyphosate was detected more frequently in 12 urban streams than in 88 agricultural streams, and at concentrations similar to those in streams with high agricultural land use (> 40% row crop) in the watershed. In contrast, atrazine was detected more frequently and at higher concentrations in agricultural streams than in urban streams. The maximum concentration of glyphosate measured at most urban sites exceeded the maximum atrazine concentration, whereas at agricultural sites the reverse was true. Measurement at a 2-day interval at 8 sites in northern Missouri revealed that transport of both herbicide compounds appeared to be controlled by spring flush, that peak concentration duration was brief, but that peaks in atrazine concentrations were of longer duration than those of glyphosate. The 2-day sampling also indicated that weekly sampling is unlikely to capture peak concentrations of glyphosate and atrazine.

Science of the Total Environment↗

USGS2009

Trends in concentrations and use of agricultural herbicides for Corn Belt rivers, 1996-2006

Trends in the concentrations and agricultural use of four herbicides (atrazine, acetochlor, metolachlor, and alachlor) were evaluated for major rivers of the Corn Belt for two partially overlapping time periods: 1996-2002 and 2000-2006. Trends were analyzed for 11 sites on the mainstems and selected tributaries in the Ohio, Upper Mississippi, and Missouri River Basins. Concentration trends were determined using a parametric regression model designed for analyzing seasonal variability, flow-related variability, and trends in pesticide concentrations(SEAWAVE-Q).TheSEAWAVE-Qmodel accounts for the effect of changing flow conditions in order to separate changes caused by hydrologic conditions from changes caused by other factors, such as pesticide use. Most of the trends in atrazine and acetochlor concentrations for both time periods were relatively small and nonsignificant, but metolachlor and alachlor were dominated by varying magnitudes of concentration downtrends. Overall, with trends expressed as a percent change per year, trends in herbicide concentrations were consistent with trends in agricultural use; 84 of 88 comparisons for different sites, herbicides, and time periods showed no significant difference between concentration trends and agricultural use trends. Results indicate that decreasing use appears to have been the primary cause for the concentration downtrends during 1996-2006 and that, while there is some evidence that nonuse management factors may have reduced concentrations in some rivers, reliably evaluating the influence of these factors on pesticides in large streams and rivers will require improved, basin-specific information on both management practices and use over time. ?? 2009 American Chemical Society.

Environmental Science & Technology↗

USGS2017

Occurrence of dichloroacetamide herbicide safeners and co-applied herbicides in midwestern U.S. streams

Dichloroacetamide safeners (e.g., AD-67, benoxacor, dichlormid, and furilazole) are co-applied with chloroacetanilide herbicides to protect crops from herbicide toxicity. While such safeners have been used since the early 1970s, there are minimal data about safener usage, occurrence in streams, or potential ecological effects. This study focused on one of these research gaps, occurrence in streams. Seven Midwestern U.S. streams (five in Iowa and two in Illinois), with extensive row-crop agriculture, were sampled at varying frequencies from spring 2016 through summer 2017. All four safeners were detected at least once; furilazole was the most frequently detected (31%), followed by benoxacor (29%), dichlormid (15%), and AD-67 (2%). The maximum concentrations ranged from 42 to 190 ng/L. Stream detections and concentrations of safeners appear to be driven by a combination of timing of application (spring following herbicide application) and precipitation events. Detected concentrations were below known toxicity levels for aquatic organisms.

Illinois, Iowa↗

USGS2026

End-user needs for remote sensing wetlands of the Prairie Pothole Region of North America

The Prairie Pothole Region (PPR) of North America comprises globally important grassland and wetland ecosystems critical for numerous populations of migratory birds. Due to the importance of this region for migratory birds, and particularly waterfowl, and the threats of habitat loss due to intensifying agriculture, there is a mature and diverse system of conservation organizations, agencies, and partnerships that spends hundreds of millions of dollars annually on habitat conservation to support migratory bird populations. Remote sensing can be a powerful tool for observing and evaluating global change at large scales as well as expanding inferences from field studies to the broader landscape with statistical models. However, development and utilization of these tools has lagged behind their demand for several reasons, including concerns over spatial and temporal resolution and accuracy of products; perception of a misalignment with decision-maker needs; technological barriers such as skill sets of conservation professionals, computing resources, data access, and usability. In this report, we summarize the needs of conservation professionals and scientists who use or want to use remote sensing data products to inform science about wetland change and conservation of wetlands in the PPR. We assembled this information through several methods leading up to, during, and following a January 2026 PPR Wetland Remote Sensing Workshop. The workshop included United States and Canadian scientists, conservation professionals, and policy experts. Our goal was to bring together end-users and remote sensing product developers jointly to explore reducing the lag between product development and utilization of products to inform science and conservation. Specifically, we aimed to identify gaps in wetland remote sensing that limit effective monitoring, management, and conservation in the PPR, and to develop a framework that outlines pathways to address these gaps by fostering collaboration, improving communication networks, encouraging discussion, and building on existing and ongoing efforts. This report summarizes our participants’ descriptions of end-user needs and the outcomes of the workshop.

Prairie Pothole region↗

USGS2025

Streamflow as a stressor: Disentangling hydrology and water quality impacts to characterize flow-ecology relationships for two stream assemblages across two southeastern landscapes

Disassociating the independent effects of flow and water quality on the ecology of flowing waters is an overarching goal in water resource science needed to improve the efficacy of watershed management. However, the interrelatedness of these gradients and their subsequent alteration due to land use change has constrained progress made on this front. The objective of this study was to use benthic macroinvertebrate and fish assemblage data to characterize flow-ecology relationships that were unchanged by water quality impacts across two southeastern landscapes in the USA to help detect ecological change driven by flow alteration. General linear latent models were used to identify taxa that were responsive to high or low flow metrics and water quality gradients. Bayesian hierarchical generalized additive models were then developed using these indicator taxa and three biological metrics to identify flow-specific relationships that were unaffected by water quality impacts. Three low flow-specific relationships were identified, illustrating how potential agricultural or urban impacts to hydrology reduced stream biological health. Importantly, flow-ecology relationships developed using indicator taxa in this study effectively captured hydrology-specific impacts while biological metrics typical of state monitoring and assessment programs did not. Therefore, developing flow-specific biological metrics is a critical step when developing management strategies targeting flow alteration. Implementing standardized frameworks such as the one characterized here can limit contradictory findings and improve streamflow enhancement and restoration project efficacy. These low flow-specific relationships will enhance managers' capacity to develop environmental flow standards, monitor their success, and better understand urban and agricultural impacts on stream assemblages.

Alabama↗

USGS2025

Mapping bedrock outcrops in the Sierra Nevada Mountains (California, USA) using machine learning

Accurate, high-resolution maps of bedrock outcrops can be valuable for applications such as models of land–atmosphere interactions, mineral assessments, ecosystem mapping, and hazard mapping. The increasing availability of high-resolution imagery can be coupled with machine learning techniques to improve regional bedrock outcrop maps. In the United States, the existing 30 m U.S. Geological Survey (USGS) National Land Cover Database (NLCD) tends to misestimate extents of barren land, which includes bedrock outcrops. This impacts many calculations beyond bedrock mapping, including soil carbon storage, hydrologic modeling, and erosion susceptibility. Here, we tested if a machine learning (ML) model could more accurately map exposed bedrock than NLCD across the entire Sierra Nevada Mountains (California, USA). The ML model was trained to identify pixels that are likely bedrock from 0.6 m imagery from the National Agriculture Imagery Program (NAIP). First, we labeled exposed bedrock at twenty sites covering more than 83 km 2 (0.13%) of the Sierra Nevada region. These labels were then used to train and test the model, which gave 83% precision and 78% recall, with a 90% overall accuracy of correctly predicting bedrock. We used the trained model to map bedrock outcrops across the entire Sierra Nevada region and compared the ML map with the NLCD map. At the twenty labeled sites, we found the NLCD barren land class, even though it includes more than just bedrock outcrops, accounted for only 41% and 40% of mapped bedrock from our labels and ML predictions, respectively. This substantial difference illustrates that ML bedrock models can have a role in improving land-cover maps, like NLCD, for a range of science applications.

California↗

USGS2023

Per- and polyfluorinated alkyl substances (PFAS) in Pennsylvania surface waters: A statewide assessment, associated sources, and land-use relations

The objectives of this study are to identify per- and polyfluoroalkyl substances (PFAS) in Pennsylvania surface waters, corresponding associations with potential sources of PFAS contamination (PSOC) and other parameters, and compare raw surface water concentrations to human and ecological benchmarks. Surface water samples from 161 streams were collected in September 2019 and were analyzed for 33 target PFAS and water chemistry. Land use and physical attributes in upstream catchments and geospatial counts of PSOC in local catchments are summarized. The hydrologic yield of the sum of 33 PFAS (∑PFAS) for each stream was computed by normalizing each site's load by the drainage area of the upstream catchment. Utilizing conditional inference tree analysis, the percentage of development (>7.58 %) was identified as a primary driver of the ∑PFAS hydrologic yields. When percentage of development was removed from analysis, ∑PFAS yields were closely related to surface water chemistry associated with landscape alteration (e.g., development or agricultural cropland), such as concentrations of total nitrogen, chloride, and ammonia, but also to count of water pollution control facilities (agricultural, industrial, stormwater, and/or municipal waste pollution abatement facilities). In oil and gas development regions, ∑PFAS yields were associated with combined sewage outfalls. Sites surrounded by ≥2 electronic manufacturing facilities had elevated ∑PFAS yields (median = 241 ng/s/km 2 ). Study results are critical to guide future research, regulatory policy, best practices that will mitigate PFAS contamination, and the communication of human health and ecological risks associated with PFAS exposure from surface waters.

Pennsylvania↗

USGS2014

Mycotoxins: diffuse and point source contributions of natural contaminants of emerging concern to streams

To determine the prevalence of mycotoxins in streams, 116 water samples from 32 streams and three wastewater treatment plant effluents were collected in 2010 providing the broadest investigation on the spatial and temporal occurrence of mycotoxins in streams conducted in the United States to date. Out of the 33 target mycotoxins measured, nine were detected at least once during this study. The detections of mycotoxins were nearly ubiquitous during this study even though the basin size spanned four orders of magnitude. At least one mycotoxin was detected in 94% of the 116 samples collected. Deoxynivalenol was the most frequently detected mycotoxin (77%), followed by nivalenol (59%), beauvericin (43%), zearalenone (26%), β-zearalenol (20%), 3-acetyl-deoxynivalenol (16%), α-zearalenol (10%), diacetoxyscirpenol (5%), and verrucarin A (1%). In addition, one or more of the three known estrogenic compounds (i.e. zearalenone, α-zearalenol, and β-zearalenol) were detected in 43% of the samples, with maximum concentrations substantially higher than observed in previous research. While concentrations were generally low (i.e. < 50 ng/L) during this study, concentrations exceeding 1000 ng/L were measured during spring snowmelt conditions in agricultural settings and in wastewater treatment plant effluent. Results of this study suggest that both diffuse (e.g. release from infected plants and manure applications from exposed livestock) and point (e.g. wastewater treatment plants and food processing plants) sources are important environmental pathways for mycotoxin transport to streams. The ecotoxicological impacts from the long-term, low-level exposures to mycotoxins alone or in combination with complex chemical mixtures are unknown

Science of the Total Environment↗

USGS2020

Landscape drivers of dynamic change in water quality of US rivers

Water security is a top concern for social well-being and dramatic changes in the availability of freshwater have occurred as a result of human uses and landscape management. Elevated nutrient loading and perturbations to major ion composition have resulted from human activities and have degraded freshwater resources. This study addresses the emerging nature of stream water quality in the 21st century through analysis of concentrations and trends in a wide variety of constituents in streams and rivers of the U.S. Concentrations of fifteen separate water quality parameters including nutrients, major ions, sediment, and specific conductance were analyzed over the period 1982-2012 and a targeted trend analysis was performed from 1992-2012. Although environmental policy is geared toward addressing the long-standing problem of nutrient overenrichment, these efforts have had uneven success, with decreasing nutrient concentrations at urbanized sites and little to no change at agricultural sites. However, freshwaters are being salinized rapidly in all human-dominated land use types. Increasing salinity negatively affects biodiversity, mobilizes sediment-bound contaminants, and increases lead contamination of drinking water but the effects are poorly quantified. Therefore, while efforts to control nutrients are ongoing, rapid salinity increases are ushering in a new set of poorly-defined issues.

Environmental Science & Technology↗

USGS2010

Using a distribution and conservation status weighted hotspot approach to identify areas in need of conservation action to benefit Idaho bird species

Identification of biodiversity hotspots (hereafter, hotspots) has become a common strategy to delineate important areas for wildlife conservation. However, the use of hotspots has not often incorporated important habitat types, ecosystem services, anthropogenic activity, or consistency in identifying important conservation areas. The purpose of this study was to identify hotspots to improve avian conservation efforts for Species of Greatest Conservation Need (SGCN) in the state of Idaho, United States. We evaluated multiple approaches to define hotspots and used a unique approach based on weighting species by their distribution size and conservation status to identify hotspot areas. All hotspot approaches identified bodies of water (Bear Lake, Grays Lake, and American Falls Reservoir) as important hotspots for Idaho avian SGCN, but we found that the weighted approach produced more congruent hotspot areas when compared to other hotspot approaches. To incorporate anthropogenic activity into hotspot analysis, we grouped species based on their sensitivity to specific human threats (i.e., urban development, agriculture, fire suppression, grazing, roads, and logging) and identified ecological sections within Idaho that may require specific conservation actions to address these human threats using the weighted approach. The Snake River Basalts and Overthrust Mountains ecological sections were important areas for potential implementation of conservation actions to conserve biodiversity. Our approach to identifying hotspots may be useful as part of a larger conservation strategy to aid land managers or local governments in applying conservation actions on the ground.

Idaho↗

USGS2013

Recent land-use/land-cover change in the Central California Valley

Open access to Landsat satellite data has enabled annual analyses of modern land-use and land-cover change (LULCC) for the Central California Valley ecoregion between 2005 and 2010. Our annual LULCC estimates capture landscape-level responses to water policy changes, climate, and economic instability. From 2005 to 2010, agriculture in the region fluctuated along with regulatory-driven changes in water allocation as well as persistent drought conditions. Grasslands and shrublands declined, while developed lands increased in former agricultural and grassland/shrublands. Development rates stagnated in 2007, coinciding with the onset of the historic foreclosure crisis in California and the global economic downturn. We utilized annual LULCC estimates to generate interval-based LULCC estimates (2000–2005 and 2005–2010) and extend existing 27 year interval-based land change monitoring through 2010. Resulting change data provides insights into the drivers of landscape change in the Central California Valley ecoregion and represents the first, continuous, 37 year mapping effort of its kind.

California↗

USGS2011

Project plan-Surficial geologic mapping and hydrogeologic framework studies in the Greater Platte River Basins (Central Great Plains) in support of ecosystem and climate change research

The Greater Platte River Basin area spans a central part of the Midcontinent and Great Plains from the Rocky Mountains on the west to the Missouri River on the east, and is defined to include drainage areas of the Platte, Niobrara, and Republican Rivers, the Rainwater Basin, and other adjoining areas overlying the northern High Plains aquifer. The Greater Platte River Basin contains abundant surficial deposits that were sensitive to, or are reflective of, the climate under which they formed: deposits from multiple glaciations in the mountain headwaters of the North and South Platte Rivers and from continental ice sheets in eastern Nebraska; fluvial terraces (ranging from Tertiary to Holocene in age) along the rivers and streams; vast areas of eolian sand in the Nebraska Sand Hills and other dune fields (recording multiple episodes of dune activity); thick sequences of windblown silt (loess); and sediment deposited in numerous lakes and wetlands. In addition, the Greater Platte River Basin overlies and contributes surface water to the High Plains aquifer, a nationally important groundwater system that underlies parts of eight states and sustains one of the major agricultural areas of the United States. The area also provides critical nesting habitat for birds such as plovers and terns, and roosting habitat for cranes and other migratory birds that travel through the Central Flyway of North America. This broad area, containing fragile ecosystems that could be further threatened by changes in climate and land use, has been identified by the USGS and the University of Nebraska-Lincoln as a region where intensive collaborative research could lead to a better understanding of climate change and what might be done to adapt to or mitigate its adverse effects to ecosystems and to humans. The need for robust data on the geologic framework of ecosystems in the Greater Platte River Basin has been acknowledged in proceedings from the 2008 Climate Change Workshop and in draft reports by researchers developing a multidisciplinary science plan for the Greater Platte River Basin.

Open-File Report↗

USGS2006

Atmospheric deposition of current-use and historic-use pesticides in snow at National Parks in the Western United States

The United States (U.S.) National Park Service has initiated research on the atmospheric deposition and fate of semi-volatile organic compounds in its alpine, sub-Arctic, and Arctic ecosystems in the Western U.S. Results for the analysis of pesticides in seasonal snowpack samples collected in spring 2003 from seven national parks are presented herein. From a target analyte list of 47 pesticides and degradation products, the most frequently detected current-use pesticides were dacthal, chlorpyrifos, endosulfan, and ??- hexachlorocyclohexane, whereas the most frequently detected historic-use pesticides were dieldrin, ??-hexachlorocyclohexane, chlordane, and hexachlorobenzene. Correlation analysis with latitude, temperature, elevation, particulate matter, and two indicators of regional pesticide use reveal that regional current and historic agricultural practices are largely responsible for the distribution of pesticides in the national parks in this study. Pesticide deposition in the Alaskan parks is attributed to long-range transport because there are no significant regional pesticide sources. The percentage of total pesticide concentration due to regional transport (%RT) was calculated for the other parks. %RT was highest at parks with higher regional cropland intensity and for pesticides with lower vapor pressures and shorter half-lives in air. ?? 2006 American Chemical Society.

Environmental Science & Technology↗

USGS2021

Streamflow response to potential changes in climate in the Upper Rio Grande Basin

The Rio Grande is a vital water source for the southwestern States of Colorado, New Mexico, and Texas and for northern Mexico. The river serves as the primary source of water for irrigation in the region, has many environmental and recreational uses, and is used by more than 13 million people including those in the Cities of Albuquerque and Las Cruces, New Mexico; El Paso, Texas; and Ciudad Juárez, Chihuahua, Mexico. However, concern is growing over the increasing gap between water supply and demand in the Upper Rio Grande Basin. As populations increase and agricultural crop patterns change, demands for water are increasing, at the same time the region is undergoing a decrease in supply due to drought and climate change. Quantifying the impact of projected climate change on Rio Grande streamflow is difficult because of numerous anthropogenic influences on the hydrologic system. The conveyance and use of surface water in the Upper Rio Grande Basin are achieved through an engineered system of reservoirs, diversions, and irrigation canals designed to deliver water to agricultural, municipal, and industrial users, who greatly reduce the cumulative volume of water in the river. For example, streamflow at Fort Quitman, Tex., the southernmost point of the Upper Rio Grande Basin, has undergone a 95-percent reduction in flow relative to the river’s native state, and some stretches of the river can intermittently go dry. Because streamflow in the basin is highly altered, disentangling the impacts of climate change and changes in streamflow due to anthropogenic influences such as dams, diversions, and other forms of water use is difficult. Therefore, a model of naturalized flow was developed to determine to what degree changes in streamflow can be attributed to potential changes in future temperature and precipitation without quantifying future changes in anthropogenic influences. This study, conducted by the U.S. Geological Survey in cooperation with the South Central Climate Adaptation Science Center and the U.S. Army Corps of Engineers, included the development and calibration of a watershed model of the Upper Rio Grande Basin using the Precipitation-Runoff Modeling System to simulate naturalized streamflow conditions for historical and future time periods.

Colorado, New Mexico, Texas↗

USGS2017

Satellite-based water use dynamics using historical Landsat data (1984–2014) in the southwestern United States

Remote sensing-based field-scale evapotranspiration (ET) maps are useful for characterizing water use patterns and assessing crop performance. The relative impact of climate variability and water management decisions are better studied and quantified using historical data that are derived using a set of consistent datasets and methodology. Historical (1984–2014) Landsat-based ET maps were generated for major irrigation districts in California, i.e., Palo Verde and eight other sub-basins in parts of the middle and lower Central Valley. A total of 3396 Landsat images were processed using the Operational Simplified Surface Energy Balance (SSEBop) model that integrates weather and remotely sensed images to estimate monthly and annual ET within the study sites over the 31 years. Model output evaluation and validation using gridded-flux data and water balance ET approaches indicated relatively good correspondence (R 2 up to 0.88, root mean square error as low as 14 mm/month) between SSEBop ET and validation datasets. In a pairwise comparison, annual variability of agro-hydrologic parameters of actual evapotranspiration ( ET a ), land surface temperature ( T s ), and runoff ( Q ) were found to be more variable than their corresponding climatic counterparts of atmospheric water demand ( ET o ), air temperature ( T a ), and precipitation ( P ), revealing process differences between regional climatic drivers and localized agro-hydrologic responses. However, only T a showed a consistent increase (up to 1.2 K) over study sites during the 31 years, whereas other climate variables such as ET o and P showed a generally neutral trend. This study demonstrates a useful application of “Big Data” science where large volumes of historical Landsat and weather datasets were used to quantify and understand the relative importance of water management and climate variability in crop water use dynamics in regards to the linkages among water management decisions, hydrologic processes and economic transactions. Irrigation district-wide ET a estimates were used to compute historical crop water use volumes and monetary equivalents of water savings for the Palo Verde Irrigation District (PVID). During the peak crop fallowing year in PVID, the water saved reached a maximum of ~ 107,200 acre-feet in 2011 with an estimated monetary payout value of $20.5 million. A significant decreasing trend in actual ET despite an increasing atmospheric demand in PVID highlights the role of management decisions in affecting local hydrologic processes. This study has importance for planning water resource allocation, managing water rights, sustaining agricultural production, and quantifying impacts of climate and land use/land cover changes on water resources. With increased computational efficiency, similar studies can be conducted in other parts of the world to help policy and decision makers understand and quantify various aspects of water resources management.

Arizona, California↗

USGS2021

Endangered Australian top predator is frequently exposed to anticoagulant rodenticides

Anticoagulant rodenticides (ARs) used to control mammalian pest populations cause secondary exposure of predatory species throughout much of the world. It is important to understand the drivers of non-target AR exposure patterns as context for assessing long-term effects and developing effective mitigation for these toxicants. In Australia, however, little is known about exposure and effects of ARs on predators. We detected AR residues in 74% of 50 opportunistically collected carcasses of the Tasmanian wedge-tailed eagle ( Aquila audax fleayi ), an endangered apex predator. In 22% of birds tested, or 31% of those exposed, liver concentrations of second generation ARs (SGARs) were >0.1 mg/kg ww. Eagles were exposed to flocoumafen, a toxicant only available from agricultural suppliers, at an exceptionally high rate (40% of birds tested). Liver SGAR concentrations were positively associated with the proportion of agricultural habitat and human population density in the area around where each eagle died. The high exposure rate in a species not known to regularly prey upon synanthropic rodents supports the hypothesis that apex predators are vulnerable to SGARs. Our results indicate that AR exposure constitutes a previously unrecognized threat to Tasmanian wedge-tailed eagles and highlight the importance of efforts to address non-target AR exposure in Australia.

Tasmania↗

USGS1998

Occurrence of pesticides in shallow groundwater of the United States: initial results from the National Water-Quality Assessment program

The first phase of intensive data collection for the National Water-Quality Assessment (NAWQA) was completed during 1993−1995 in 20 major hydrologic basins of the United States. Groundwater land-use studies, designed to sample recently recharged groundwater (generally within 10 years) beneath specific land-use and hydrogeologic settings, are a major component of the groundwater quality as sessment for NAWQA. Pesticide results from the 41 land-use studies conducted during 1993−1995 indicate that pesticides were commonly detected in shallow groundwater, having been found at 54.4% of the 1034 sites sampled in agricultural and urban settings across the United States. Pesticide concentrations were generally low, with over 95% of the detections at concentrations less than 1 μg/L. Of the 46 pesticide compounds examined, 39 were detected. The compounds detected most frequently were atrazine (38.2%), deethylatrazine (34.2%), simazine (18.0%), metolachlor (14.6%), and prometon (13.9%). Statistically significant relations were observed between frequencies of detection and the use, mobility, and persistence of these compounds. Pesticides were commonly detected in both agricultural (56.4%; 813 sites) and urban (46.6%; 221 sites) settings. Frequent detections of pesticides in urban areas indicate that, as is the case with agricultural pesticide use in agricultural areas, urban and suburban pesticide use significantly contribute to pesticide occurrence in shallow groundwater. Although pesticides were detected in groundwater sampled in urban areas and all nine of the agricultural land-use categories examined, significant variations in occurrence were observed among these categories. Maximum contaminant levels (MCLs) established by the U.S. Environmental Protection Agency for drinking water were exceeded for only one pesticide (atrazine, 3 μg/L) at a single location. However, MCLs have been established for only 25 of the 46 pesticide compounds examined, do not cover pesticide degradates, and, at present, do not take into account additive or synergistic effects of combinations of pesticide compounds or potential effects on nearby aquatic ecosystems.

Environmental Science & Technology↗