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At least 253 records · Page 14Linked to original sources
USGS2023

A general approach for evaluating of the coverage, resolution, and representation of streamflow monitoring networks

Streamflow monitoring networks provide information for a wide range of public interests in river and streams. A general approach to evaluate monitoring for different interests is developed to support network planning and design. The approach defines three theoretically distinct information metrics (coverage, resolution, and representation) based on the spatial distribution of a variable of interest. Coverage is the fraction of information that a network can provide about a variable when some areas are not monitored. Resolution is the information available from the network relative to the maximum information possible given the number of sites in the network. Representation is the information that a network provides about a benchmark distribution of a variable. Information is defined using Shannon entropy where the spatial discretization of a variable among spatial elements of a landscape or sites in a network indicates the uncertainty in the spatial distribution of the variable. This approach supports the design of networks for monitoring of variables with heterogeneous spatial distributions (“hot spots” and patches) that might otherwise be unmonitored because they occupy insignificant portions of the landscape. Areas where monitoring will maintain or improve the metrics serve as objective priorities for public interests in network design. The approach is demonstrated for the streamflow monitoring network operated by the United States Geological Survey during water year 2020 indicating gaps in the coverage of coastal rivers and the resolution of low flows.

Colorado↗
USGS2023

Differing field methods and site conditions lead to varying bias in suspended sediment concentrations in the Lower Mississippi and Atchafalaya Rivers

At sites that have been sampled for decades, changes in field and laboratory methods happen over time as instrumentation and protocols improve. Here, we compare the influence of depth- and point-integrated sampling on total, fine (< 0.0625 mm), and coarse (≥ 0.0625 mm) suspended sediment (SS) concentrations in the Lower Mississippi and Atchafalaya Rivers. Using historical field method information, we identified seven sites to test such differences. We found SS samples collected using point-integration tended to have higher concentrations than those collected using depth-integration. However, the presence and magnitude of the bias were inconsistent across sites. Bias was present at the site with less-than-ideal conditions (i.e., non-trapezoidal channel, non-uniform flow) and non-existent at the ideal site location, indicating the bias between sampling methods depends on site sampling conditions. When present, the bias is greater at higher concentrations and at moderate to high flows. At the less-than-ideal site, point-integrated samples can have 16% (total) and 34% (coarse) higher concentrations than depth-integrated samples. When flow effects are removed, this translates to a bias of 19, 9, and 8 mg per liter for total, fine, and coarse SS. When a change in field methods occurs, comparison samples and a rigorous evaluation of those samples are warranted to determine the proper course of action for a particular site. Often, the effect and solution will not be known until several years of comparison samples have been collected under a variety of hydrologic conditions.

Louisiana↗
USGS2024

Prioritizing river basins for nutrient studies

Increases in fluxes of nitrogen (N) and phosphorus (P) in the environment have led to negative impacts affecting drinking water, eutrophication, harmful algal blooms, climate change, and biodiversity loss. Because of the importance, scale, and complexity of these issues, it may be useful to consider methods for prioritizing nutrient research in representative drainage basins within a regional or national context. Two systematic, quantitative approaches were developed to (1) identify basins that geospatial data suggest are most impacted by nutrients and (2) identify basins that have the most variability in factors affecting nutrient sources and transport in order to prioritize basins for studies that seek to understand the key drivers of nutrient impacts. The “impact” approach relied on geospatial variables representing surface-water and groundwater nutrient concentrations, sources of N and P, and potential impacts on receptors (i.e., ecosystems and human health). The “variability” approach relied on geospatial variables representing surface-water nutrient concentrations, factors affecting sources and transport of nutrients, model accuracy, and potential receptor impacts. One hundred and sixty-three drainage basins throughout the contiguous United States were ranked nationally and within 18 hydrologic regions. Nationally, the top-ranked basins from the impact approach were concentrated in the Midwest, while those from the variability approach were dispersed across the nation. Regionally, the top-ranked basin selected by the two approaches differed in 15 of the 18 regions, with top-ranked basins selected by the variability approach having lower minimum concentrations and larger ranges in concentrations than top-ranked basins selected by the impact approach. The highest ranked basins identified using the variability approach may have advantages for exploring how landscape factors affect surface-water quality and how surface-water quality may affect ecosystems. In contrast, the impact approach prioritized basins in terms of human development and nutrient concentrations in both surface water and groundwater, thereby targeting areas where actions to reduce nutrient concentrations could have the largest effect on improving water availability and reducing ecosystem impacts.

Environmental Monitoring and Assessment↗
USGS2024

Prioritizing water availability study settings to address geogenic contaminants and related societal factors

Water availability for human and ecological uses depends on both water quantity and water quality. The U.S. Geological Survey (USGS) is developing strategies for prioritizing regional-scale and watershed basin-scale studies of water availability across the nation. Previous USGS ranking processes for basin-scale studies incorporated primarily water quantity factors but are now considering additional water quality factors. This study presents a ranking based on the potential impacts of geogenic constituents on water quality and consideration of societal factors related to water quality. High-concentration geogenic constituents, including trace elements and radionuclides, are among the most prevalent contaminants limiting water availability in the USA and globally. Geogenic constituents commonly occur in groundwater because of subsurface water–rock interactions, and their distributions are controlled by complex geochemical processes. Geogenic constituent mobility can also be affected by human activities (e.g., mining, energy production, irrigation, and pumping). Societal factors and relations to drinking water sources and water quality information are often overlooked when evaluating research priorities. Sociodemographic characteristics, data gaps resulting from historical data-collection disparities, and infrastructure condition/age are examples of factors to consider regarding environmental justice. This paper presents approaches for ranking and prioritizing potential basin-scale study areas across the contiguous USA by considering a suite of conventional physical and geochemical variables related to geogenic constituents, with and without considering variables related to societal factors. Simultaneous consideration of societal and conventional factors could provide decision makers with more diverse, interdisciplinary tools to increase equity and reduce bias in prioritizing focused research areas and future water availability studies.

Environmental Monitoring and Assessment↗
USGS2025

6PPD-quinone in water from the Sacramento-San Joaquin Delta, California, 2018-2024

The Sacramento-San Joaquin Delta (Delta) is an expansive river delta supplying a large portion of California’s fresh water for agriculture and residential use, and it is also an area of critical habitat for numerous state and federally listed species of concern. In many locations, urban stormwater flows directly into the Delta. 6PPD-quinone (6PPD-Q), an ozonation byproduct of a tire antiozonant 6PPD, has been shown to enter surface water via these pathways and can cause various toxicological effects, including acute urban mortality syndrome to coho salmon ( Oncorhynchus kisutch ) at low levels (LC 50 = 41 and 95 ng/L for juveniles and adults, respectively). Here, we quantified 6PPD-Q in 61 archived Delta water extracts collected between 2018 and 2024 and found concentrations up to 21 ng/L. Currently, no 6PPD-Q presence and/or quantitative data is available for this complex and diverse ecosystem. Little is known regarding long-term storage of 6PPD-quinone in solvent extracts, so 6PPD-Q observations document its presence in the study area and provide evidence that further sampling may be warranted to better quantify environmental concentrations. Consistent with the general understanding of 6PPD-Q transport, all detections observed were in samples collected during or immediately after a precipitation event. This work provides environmentally relevant concentration data to complement ongoing toxicological investigations of 6PPD-Q in Delta organisms and suggests there are research opportunities for a more robust survey of 6PPD-Q inputs into the Delta.

California↗
USGS2025

Expansion of aquatic and marsh area into once forest and agricultural area reflects changing hydrological conditions along the Upper Mississippi and Illinois rivers (1989-2020)

We examined 30-year trends in the abundance and distribution of aquatic and floodplain vegetation, as well as human land uses in five study reaches of the Upper Mississippi River and one reach of the Illinois River using aerial photography collected in years 1989, 2000, 2010, and 2020. Permanently inundated area increased in all study reaches over the 30-year period. Increases ranged from 0.8% of study reach area in Pool 8 (73 ha) to as much as 6.5% of study reach area in Pool 13 (1,562 ha). Agricultural land use declined in the three study reaches where it was common (>35% of reach area). Agricultural declines ranged from 5.8% of reach area in Pool 26 (2,096 ha) to as much as 15.4% of reach area in the Open River reach (7,121 ha) and corresponded with a similar magnitude increase in permanently inundated area and semi-permanently inundated marsh classes. Total forest area declined in the four northern study reaches of the Upper Mississippi River. Forest loss estimates were on the order of 3.7% of study reach area in Pool 13 (905 ha), 2.1% of Pool 8 (364 ha), and 2.3% of Pool 4 (563 ha). Such losses represent 16.2%, 13.2%, and 10.9% of the total forest area in 1989 in Pools 13, 8 and 4, respectively. Permanently inundated area, wet meadow, shallow marsh vegetation, and mud were the main cover types that replaced forest cover in these reaches. In contrast to the decline in forest cover in the northern reaches, forest cover remained unchanged in the La Grange reach of the Illinois River and increased by 3.5% of study reach area (1,607 ha) in the southern Open River reach of the Mississippi River, mainly in former marsh vegetation and agricultural areas that were acquired by Federal and State agencies. The predominant changes observed across the study system (replacement of agriculture and forest area by permanently inundated area and semi-permanently inundated marsh classes) indicates that hydrological changes have been the main driver of change since 1989 throughout most of the Upper Mississippi and Illinois Rivers. Our study provides an example of changes in a regulated river system driven by regional-scale hydrological changes and local scale restoration actions, changes that could be compared against changes occurring in other large, regulated rivers across the globe.

Illinois, Iowa, Minnesota, Missouri, Wisonsin↗
USGS2025

Spatiotemporal drivers of water quality and phytoplankton communities in a cyanobacteria-dominated reservoir provide management insights

Reservoirs serve critical roles providing drinking water, irrigation, flood control, hydropower, recreation, fisheries, and aquatic habitat. Yet their physical position, complex shape, and large watersheds make reservoirs especially susceptible to eutrophication and harmful algal bloom (HAB) production. Boysen Reservoir, WY, is a high priority for proactive nutrient management because it is an important source for drinking water and recreation, and has a history of toxic cyanobacterial blooms. We combined four years of comprehensive monitoring efforts by state and federal agencies to characterize the spatiotemporal patterns of nutrient inflow, internal water quality dynamics, and phytoplankton community shifts in Boysen Reservoir. We found nutrient inflow was hydrologically driven, with snowmelt runoff transporting high nutrient loads. Our findings suggest physicochemical and nutrient conditions of the reservoir were strongly different between the furthest reaches of the reservoir, but less variable among the intermediate sites. Space did not play a role in phytoplankton community dynamics, but time was an important factor. Cyanobacteria dominated phytoplankton communities by mid-summer across the reservoir and were driven mainly by temporal physicochemical conditions, like stratification and water temperature. The two most dominant phytoplankton taxa across the four years of sampling were N-fixing, toxin producing cyanobacteria. Extensive monitoring efforts and data analyses can illuminate strategies to safeguard water resources via understanding the drivers of water quality changes and HAB production.

Wyoming↗
USGS2025

From sample to sonde to Sentinel-2: Insights from a multi-scale chlorophyll-a monitoring effort in the Hudson River, New York

Monitoring cyanobacteria and other nuisance phytoplankton in the Hudson River is of great interest given its societal and ecological importance. Satellite remote sensing provides a cost-effective method to monitor chlorophyll- a (chl-a), a common proxy for algal biomass; however, the dynamic nature of rivers complicates approaches traditionally applied to lakes and oceans. During 2021–2023, we collected discrete samples for laboratory measurement of chl-a and measured in situ chl-a fluorescence during a series of longitudinal boat surveys along a 220-km reach of the lower Hudson River. Surveys were timed to coincide with Sentinel-2 satellite overpasses. We first investigated relations between laboratory-measured chl-a concentration and field-measured chl-a fluorescence, observing a weak correlation ( r 2 = 0.25) that improved substantially after splitting data by day (mean r 2 = 0.53). Separately, to estimate chl-a fluorescence using satellite data, we developed a series of random forest models leveraging the rich fluorescence dataset collected. We tested three model types: individual day models, leave-one-out models trained on all days except a holdout test day, and a single pooled model trained on all days. Generally, individual day models exhibited lowest error (mean of mean absolute error [MAE] = 0.16 relative fluorescence units [RFU]), followed by the single pooled model (MAE = 0.22 RFU). Daily holdout models showed highest error (mean MAE = 0.40 RFU); this approach was intended to represent model performance on a day unseen in the training set, providing a more conservative estimate of performance than the more traditional pooled approach. Findings from both analyses emphasize the importance of considering temporal variability when modeling riverine systems.

New Jersey, New York↗
USGS1997

A study of the temporal variability of atrazine in private well water. Part I: Study design, implementation, and database development

In 1988, the Iowa Department of Natural Resources, along with the University of Iowa conducted the Statewide Rural Well Water Survey, commonly known as SWRL. A total of 686 private rural drinking water wells was selected by use of a probability sample and tested for pesticides and nitrates. Sixty-eight of these wells, the '10% repeat' wells, were additionally sampled in October, 1990 and June, 1991. Starting in November, 1991, the University of Iowa, with sponsorship from the United States Environmental Protection Agency, revisited these wells to begin a study of the temporal variability of atrazine and nitrates in wells. Other wells, which had originally tested positive for atrazine in SWRL but were not in the 10% repeat population, were added to the study population. Temporal sampling for a year-long period began in February of 1992 and concluded in January of 1993. All wells were sampled monthly, one subset was sampled weekly, and a second subset was sampled for 14-day consecutive periods. Two unique aspects of this study were the use of an immunoassay technique to screen for triazines before gas chromatography/mass spectrometry (GC/MS) analysis and quantification of atrazine, and the use of well owners to sample the wells. A total of 1771 samples from 83 wells are in the final data base for this study. This paper reviews the study design, the analytical methodologies, and development of the data base. A companion paper discusses the analysis of the data from this survey.

Environmental Monitoring and Assessment↗
USGS1997

A study of the temporal variability of atrazine in private well water. part ii: analysis of data

In 1988, the Iowa Department of Natural Resources, along withthe University of Iowa, conducted the Statewide Rural WellWater Survey, commonly known as SWRL. A total of 686private rural drinking water wells was selected by use of aprobability sample and tested for pesticides and nitrate. A subsetof these wells, the 10% repeat wells, were additionally sampledin October, 1990 and June, 1991. Starting in November, 1991,the University of Iowa, with sponsorship from the United StatesEnvironmental Protection Agency, revisited the 10% repeat wellsto begin a study of the temporal variability of atrazine and nitratein wells. Other wells, which had originally tested positive foratrazine in SWRL but were not in the 10% population, wereadded to the study population. Temporal sampling for a year-long period began in February of 1992 and concluded in Januaryof 1993. All wells were sampled monthly, a subset was sampledweekly, and a second subset was sampled for 14 day consecutiveperiods. Of the 67 wells in the 10% population tested monthly,7 (10.4%) tested positive for atrazine at least once during theyear, and 3 (4%) were positive each of the 12 months. Theaverage concentration in the 7 wells was 0.10 µg/L. Fornitrate, 15 (22%) wells in the 10% repeat population monthlysampling were above the Maximum Contaminant Level of 10 mg/L at least once. This paper, the second of two papers on thisstudy, describes the analysis of data from the survey. The firstpaper (Lorber et al., 1997) reviews the study design, theanalytical methodologies, and development of the data base.

Environmental Monitoring and Assessment↗
USGS1998

Contaminants in wintering canvasbacks and scaups from San Francisco Bay, California

Organochlorines, metals, and trace elements were measured in liver, kidney, or whole-body tissues of canvasbacks (Aythya valisineria), lesser scaups ( A. affinis ), and greater scaups ( A. marila ) collected from San Francisco Bay and three coastal areas of California during the winter of 1986–1987. Potentially toxic concentrations of mercury (mean ≤10.4 µg/g, dry weight) and selenium (mean ≤32.7 µg/g, dry weight) were found in livers of scaups and canvasbacks from several San Francisco Bay sites. These elements varied spatially, temporally, and between species, with the highest concentrations found in late winter. Mean concentrations of mercury, selenium, and cadmium were generally higher in scaups than in canvasbacks. Of all the organochlorines included in the analyses, only p,p'-DDE and total PCBs were detected in all samples in this study. Mean whole-body concentrations of DDE and PCBs from San Francisco Bay ducks collected in late winter varied spatially and between species, but the concentrations were not considered toxic. Causes for inter-specific differences are unclear, but may be attributable to differences in diet, movement, or physiology.

Environmental Monitoring and Assessment↗
USGS1998

Sampling benthic macroinvertebrates in a large flood-plain river: Considerations of study design, sample size, and cost

Estimation of benthic macroinvertebrate populations over large spatial scales is difficult due to the high variability in abundance and the cost of sample processing and taxonomic analysis. To determine a cost-effective, statistically powerful sample design, we conducted an exploratory study of the spatial variation of benthic macroinvertebrates in a 37 km reach of the Upper Mississippi River. We sampled benthos at 36 sites within each of two strata, contiguous backwater and channel border. Three standard ponar (525 cm 2 ) grab samples were obtained at each site ('Original Design'). Analysis of variance and sampling cost of strata-wide estimates for abundance of Oligochaeta, Chironomidae, and total invertebrates showed that only one ponar sample per site ('Reduced Design') yielded essentially the same abundance estimates as the Original Design, while reducing the overall cost by 63%. A posteriori statistical power analysis (α = 0.05, β = 0.20) on the Reduced Design estimated that at least 18 sites per stratum were needed to detect differences in mean abundance between contiguous backwater and channel border areas for Oligochaeta, Chironomidae, and total invertebrates. Statistical power was nearly identical for the three taxonomic groups. The abundances of several taxa of concern (e.g., Hexagenia mayflies and Musculium fingernail clams) were too spatially variable to estimate power with our method. Resampling simulations indicated that to achieve adequate sampling precision for Oligochaeta, at least 36 sample sites per stratum would be required, whereas a sampling precision of 0.2 would not be attained with any sample size for Hexagenia in channel border areas, or Chironomidae and Musculium in both strata given the variance structure of the original samples. Community-wide diversity indices (Brillouin and 1-Simpsons) increased as sample area per site increased. The backwater area had higher diversity than the channel border area. The number of sampling sites required to sample benthic macroinvertebrates during our sampling period depended on the study objective and ranged from 18 to more than 40 sites per stratum. No single sampling regime would efficiently and adequately sample all components of the macroinvertebrate community.

Environmental Monitoring and Assessment↗
USGS1998

Metal and trace element burdens in two shorebird species at two sympatric wintering sites in southern California

In January and November, 1994, ten willets (Catoptrophorus semipalmatus) and ten black-bellied plovers (Pluvialis squatarola) were collected at a south-facing sandy beach at the North Island Naval Air Station (NASNI) and ten willets and three plovers were collected at the Tijuana Slough National Wildlife Refuge (TSNWR), 16 km to the southeast. Concentrations of 19 inorganic analytes were determined in the livers. Differences between sexes in diet or abilities to retain some analytes are indicated because male willets tend to have greater levels of Cd than females and male plovers tend to have greater levels of Fe, Hg, and Mn than females. Concentrations of Hg and Mg in willets decreased from January to November. If this decrease is a part of an annual cycle, then the birds may be acquiring those elements while at NASNI. The differences between sites shows higher levels of As and Se but lower levels of Mn in willets at NASNI while plovers have lower levels of Cu, Mg and Zn at NASNI. There were no correlations between Hg and Se concentrations in the livers of any sample group of birds.

California↗
USGS1999

Chlorinated hydrocarbons in livers of American mink (Mustela vison) and river otter (Lutra canadensis) from the Columbia and Fraser River Basins, 1990-1992

We investigated chlorinated hydrocarbon contaminants in aquatic mustelid species on the Fraser and Columbia Rivers of northwestern North America. Carcasses of river otter (Lutra canadensis) (N=24) and mink (Mustela vison) (N=34) were obtained from commercial trappers during the winters of 1990–91 and 1991–92. Pooled liver samples were analyzed for organochlorine pesticides, polychlorinated biphenyls (PCBs), including non-ortho congeners, polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). Most samples contained detectable concentrations of DDE, PCBs, although there was substantial variability in patterns and trends among neighboring samples. Concentrations of DDE were in some mink and several otter samples from the lower Columbia River elevated (to 4700 μg/kg wet weight); excluding one mink sample from the Wenatchee area, mean DDE levels generally decreased between 1978–79 and 1990–92. PCBs were present in all samples. PCB concentrations in otter livers collected from the lower Columbia were ten-fold lower than measured a decade previously; nevertheless, a sample taken near Portland had a mean concentration of 1500 μg/kg, within a range of concentrations associated with reproductive effects in captive mink. Concentrations of 2,3,7,8-TCDD and TCDF were generally below detection limits, except for one otter collected near a pulp mill at Castlegar, on the upper Columbia, with 11 ng TCDD/kg in liver. Elevated concentrations of higher chlorinated PCDD/Fs, probably resulting from use of chlorophenolic wood preservatives, were found in both species; one otter sample from the lower Columbia had 2200 ng OCDD/kg. International TCDD toxic equivalent levels in mink (31 ng/kg) and otter (93 ng/kg) from the lower Columbia River approached toxicity thresholds for effects on reproduction in ranch mink.

British Columbia, Oregon, Washington↗
USGS1998

Long term trends liver neoplasm epizootics of brown bullhead in the Black River, Ohio

Since 1980, liver neoplasms in brown bullhead and polynuclear aromatic hydrocarbons (PAH) in sediment have been researched in a series of studies on the Black River in Lorain, Ohio. In the early 1980s the liver cancer prevalence in fish of age 3 and older was high, ranging from 22% to 39% of the adult population. These high cancer rates corresponded to high levels of PAHs in the sediment resulting from long-term releases by an upstream coking facility (USX). In 1983 this coking plant was closed, and by 1987 the PAH in sediment had declined by about two orders of magnitude. Coincidentally the tumor prevalence in 1987 was only about one-fourth of that in the early 1980s. In 1990, the most contaminated sediments were dredged. Neoplasm surveys in 1992 and 1993 found liver tumor frequencies in mature bullhead were as high as or higher than in the early 1980s. However liver tumor incidence declined in 1994, especially among age 3 fish, where neoplasm incidence was zero. These age 3 fish were the first group sampled that were not present during the 1990 dredging. These data are consistent with a hypothesis that the increase in tumor prevalence in 1992 and 1993 was caused by exposure to buried PAH-contaminated sediments released by the dredging. This research points out the insight provided by long term effects studies.

Ohio↗
USGS1998

Regional land cover characterization using Landsat thematic mapper data and ancillary data sources

As part of the activities of the Multi-Resolution Land Characteristics (MRLC) Interagency Consortium, an intermediate-scale land cover data set is being generated for the conterminous United States. This effort is being conducted on a region-by-region basis using U.S. Standard Federal Regions. To date, land cover data sets have been generated for Federal Regions 3 (Pennsylvania, West Virginia, Virginia, Maryland, and Delaware) and 2 (New York and New Jersey). Classification work is currently under way in Federal Region 4 (the southeastern United States), and land cover mapping activities have been started in Federal Regions 5 (the Great Lakes region) and 1 (New England). It is anticipated that a land cover data set for the conterminous United States will be completed by the end of 1999. A standard land cover classification legend is used, which is analogous to and compatible with other classification schemes. The primary MRLC regional classification scheme contains 23 land cover classes. The primary source of data for the project is the Landsat thematic mapper (TM) sensor. For each region, TM scenes representing both leaf-on and leaf-off conditions are acquired, preprocessed, and georeferenced to MRLC specifications. Mosaicked data are clustered using unsupervised classification, and individual clusters are labeled using aerial photographs. Individual clusters that represent more than one land cover unit are split using spatial modeling with multiple ancillary spatial data layers (most notably, digital elevation model, population, land use and land cover, and wetlands information). This approach yields regional land cover information suitable for a wide array of applications, including landscape metric analyses, land management, land cover change studies, and nutrient and pesticide runoff modeling.

Environmental Monitoring and Assessment↗
USGS1999

The Bear Brook Watershed, Maine (BBWM), USA

The Bear Brook Watershed Manipulation project in Maine is a paired calibrated watershed study funded by the U.S. EPA. The research program is evaluating whole ecosystem response to elevated inputs of acidifying chemicals. The consists of a 2.5 year calibration period (1987-1989), nine years of chemical additions of (NH4)2SO4 (15N- and 34S-enriched for several years) to West Bear watershed (1989-1998), followed by a recovery period. The other watershed, East Bear, serves as a reference. Dosing is in six equal treatments/yr of 1800 eq SO4 and NH4/ha/yr, a 200% increase over 1988 loading (wet plus dry) for SO4 300% for N (wet NO3 + NH4). The experimental and reference watersheds are forested with mixed hard- and softwoods, and have thin acidic soils, areas of 10.2 and 10.7 ha and relief of 210 m. Thin till of variable composition is underlain by metasedimentary pelitic rocks and calc-silicate gneiss intruded by granite dikes and sills. For the period 1987-1995, precipitation averaged 1.4 m/yr, had a mean pH of 4.5, with SO4, NO3, and NH4 concentrations of 26, 14, and 7 ??eq/L, respectively. The nearly perrenial streams draining each watershed have discharges ranging from 0 (East Bear stops flowing for one to two months per year) to 150 L/sec. Prior to manipulation, East Bear and West Bear had a volume weighted annual mean pH of approximately 5.4, alkalinity = 0 to 4 ??eq/L, total base cations = 184 ??eq/L (sea-salt corrected = 118 ??eq/L), and SO4 = 100 to 111 ??eq/L. Nitrate ranged from 0 to 30 ??eq/L with an annual mean of 6 to 25 ??eq/L; dissolved organic carbon (DOC) ranged from 1 to 7 mg/L but was typically less than 3. Episodic acidification occurred at high discharge and was caused by dilution of cations, slightly increased DOC, significantly higher NO3, and the sea-salt effect. Depressions in pH were accompanied by increases in inorganic Al. The West Bear catchment responded to the chemical additions with increased export of base cations, Al, SO4, NO3, and decreased pH, ANC, and DOC. Silica remained relatively constant. Neutralization of the acidifying chemicals occurred dominantly by cation desorption and mobilization of Al.

Environmental Monitoring and Assessment↗
USGS2000

Environmental contaminants in blood, hair, and tissues of ocelots from the Lower Rio Grande Valley, Texas, 1986-1997

The ocelot (Felis pardalis) is an endangered neotropical cat distributed within a small range in the Lower Rio Grande Valley (LRGV), in Texas, U.S.A. Studies of the impacts of environmental contaminants in wild cats are few. Approximately one fourth of the estimated population (about 100) of ocelots in the LRGV was sampled to evaluate the impacts of chlorinated pesticides, polychlorinated biphenyls, and trace elements on the population. Hair was collected from 32 ocelots trapped between 1986-1992, and blood was collected from 20 ocelots trapped between 1993-1997. A few blood samples were obtained from individuals recaptured two or three times. Tissue samples from 4 road-killed ocelots were also analyzed. DDE, PCBs, and Hg were some of the most common contaminants detected in hair and blood. Mean Hg levels in hair ranged from 0.5 to 1.25 ??g g-1 dw, Se from 1.5 to 3.48 ??g g-1 dw, and Pb from 0.56 to 26.8 ??g g-1 dw. Mean DDE concentrations in plasma ranged from 0.005 ??g g-1 ww to 0.153 ??g g-1 ww, and PCBs ranged from 0.006 ??g g-1 ww to 0.092 ??g g-1 ww. Mean Hg levels in red blood cells ranged from 0.056 ??g g-1 dw to 0.25 ??g g-1 dw. Concentrations of DDE, PCBs, or Hg, did not increase significantly with age, although the highest concentrations of DDE and Hg were found in older animals. Overall, concentrations of DDE, PCBs, and Hg were low and at levels that currently do not pose any threat to health or survival of the ocelot. This is further supported by good reproduction of the ocelot in the LRGV, where adult females averaged about 1.5 kittens/litter. Thus, it seems that the current major threat to recovery of the ocelot in the LRGV may be habitat loss, although potential impacts of new generation pesticides, such as organophosphorus and carbamate insecticides need further study.The ocelot (Felis pardalis) is an endangered neotropical cat distributed within a small range in the Lower Rio Grande Valley (LRGV), in Texas, U.S.A. Studies of the impacts of environmental contaminants in wild cats are few. Approximately one fourth of the estimated population (about 100) of ocelots in the LRGV was sampled to evaluate the impacts of chlorinated pesticides, polychlorinated biphenyls, and trace elements on the population. Hair was collected from 32 ocelots trapped between 1986-1992, and blood was collected from 20 ocelots trapped between 1993-1997. A few blood samples were obtained from individuals recaptured two or three times. Tissue samples from 4 road-killed ocelots were also analyzed. DDE, PCBs, and Hg were some of the most common contaminants detected in hair and blood. Mean Hg levels in hair ranged from 0.5 to 1.25 ??g g-1 dw, Se from 1.5 to 3.48 ??g g-1 dw, and Pb from 0.56 to 26.8 ??g g-1 dw. Mean DDE concentrations in plasma ranged from 0.005 ??g g-1 ww to 0.153 ??g g-1 ww, and PCBs ranged from 0.006 ??g g-1 ww to 0.092 ??g g-1 ww. Mean Hg levels in red blood cells ranged from 0.056 ??g g-1 dw to 0.25 ??g g-1 dw. Concentrations of DDE, PCBs, or Hg, did not increase significantly with age, although the highest concentrations of DDE and Hg were found in older animals. Overall, concentrations of DDE, PCBs, and Hg were low and at levels that currently do not pose any threat to health or survival of the ocelot. This is further supported by good reproduction of the ocelot in the LRGV, where adult females averaged about 1.5 kittens/litter. Thus, it seems that the current major threat to recovery of the ocelot in the LRGV may be habitat loss, although potential impacts of new generation pesticides, such as organophosphorus and carbamate insecticides need further study.The impacts of PCBs, trace elements, and chlorinated pesticides on the endangered ocelot population in the Lower Rio Grande Valley, TX, was studied. Hair was sampled from 32 animals trapped during 1986-92 and blood was collected from 20 ocelots trapped during 1993-97. Mean mercury, selenium, and lead levels in hair were in the 0.5-1.25, 1.5-3.48, and 0.56-26.8 ??g/g

Environmental Monitoring and Assessment↗