In flowing waters with elevated selenium concentrations, fish are often considered to be at risk from selenium toxicity owing to dietary exposure and accumulation in ovarian tissues and subsequent deformities in developing larvae. We studied selenium throughout components of the aquatic food webs at geomorphically distinct locations along the oligotrophic Kootenai River (Montana and Idaho, USA), a river with moderately elevated dissolved selenium concentrations (∼ 1 µg/L). Components included water, sediment, freshly accrued biofilms, in situ periphyton, sestonic detritus, aquatic invertebrates, and fish, with spring and fall sampling. Selenium concentrations were similar among the sediment, biofilm, periphyton, and detritus samples. Among the aquatic invertebrates, the highest selenium concentrations were observed in Paraleptophlebia sp. mayflies and oligochaetes. No consistent concentration patterns with season or feeding traits were observed. Fish tissue selenium concentrations were highly variable among species and tissue type. Selenium in fish tissues tended to be highest in livers of rainbow trout and mountain whitefish relative to ovarian, muscle, and carcass tissues. With northern pikeminnow, redside shiner, and slimy sculpin, selenium concentrations tended to be highest in ovarian tissues. The trophic transfer factors of selenium from particulates to invertebrates and fish was higher in the lotic sites than in the lentic site. The results question the validity of the lotic/lentic risk paradigm for selenium beyond the small stream versus wetland/pond settings from which the paradigm was developed. Potential alternative monitoring approaches are illustrated using aquatic invertebrates or the food web monitoring results to derive monitoring targets for selenium in water or invertebrate tissue that could avoid the need to kill fish to assess whether fish protection guidelines are met.

First posted January 26, 2023 For additional information, contact: Director, Wyoming-Montana Water Science CenterU.S. Geological Survey3162 Bozeman AvenueHelena, MT 59601Contact Pubs Warehouse The Riverton Processing site was a uranium mill 4 kilometers southwest of Riverton, Wyoming, that prepared uranium ore for nuclear reactors and weapons from 1958 to 1963. The U.S. Department of Energy completed surface remediation of the uranium tailings in 1989; however, groundwater below and downgradient from the tailings site and nearby Little Wind River was not remediated. Beginning in 2010, a series of floods along the Little Wind River began to mobilize contaminants in the unsaturated zone, resulting in substantial increases of uranium and other contaminants of concern in monitoring wells completed inside the contaminant plume. In 2011, the U.S. Department of Energy started a series of university and Government agency retrospective and field investigations to understand the processes controlling contaminant increases in the groundwater plume. The goals of the field investigations described in this report were to (1) identify and quantify the contaminant flux and potential associated biological effects from groundwater associated with the legacy plume as it enters a perennial stream reach, and (2) assess chemical exposure and potential effects to biological receptors from the interaction of the contaminant plume and the river.Field investigations along the Little Wind River were completed by the U.S. Geological Survey during 2015–17 in cooperation with the U.S. Department of Energy Office of Legacy Management to characterize: (1) seepage areas and seepage rates; (2) pore-water and bed sediment chemistry and hyporheic exchange and reactive loss; and (3) exposure pathways and biological receptors. All data collected during the study are contained in two U.S. Geological Survey data releases, available at https://doi.org/10.5066/F7BR8QX4 and https://doi.org/10.5066/P9J9VJBR. A variety of tools and methods were used during the field characterizations. Streambed temperature mapping, electrical resistivity tomography, electromagnetic induction, fiber-optic distributed temperature sensing, tube seepage meters, vertical thermal sensor arrays, and an environmental tracer (radon) were used to identify areas of groundwater seepage and associated seepage rates along specific sections of the study reach of the river. Drive points, minipiezometers, diffusive equilibrium in thin-film/diffusive gradients in thin-film probes, bed-sediment samples, and equal discharge increment sampling methods were used to characterize pore-water chemistry, estimate hyporheic exchange and reactive loss of selected chemical constituents, and quantify contaminant loadings entering the study reach. Sampling and analysis of surface sediments, filamentous algae, periphytic algae, and macroinvertebrates were used to characterize biological exposure pathways, metal uptake, and receptors.Areas of focused groundwater discharge identified by the fiber-optic distributed temperature sensing surveys corresponded closely with areas of elevated electrical conductivity identified by the electromagnetic induction survey results in the top 5 meters of sediment. During three monitoring periods in 2016, the mean vertical seepage rate measured with tube seepage meters was 0.45 meter per day, ranging from −0.02 to 1.55 meters per day. Five of the 11 locations where vertical thermal profile data were collected along the study reach during August 2017 indicated mean upwelling values ranging from 0.11 to 0.23 meter per day. Radon data collected from the Little Wind River during June, July, and August 2016 indicated a consistent inflow of groundwater to the central part of the study reach, in the area congruous with the center of the previously mapped groundwater plume discharge zone. During August 2017, the greatest attenuation of uranium from reactive loss in pore-water samples was observed at three locations along the study reach, at depths between 6 and 15 centimeters, and similar trends in molybdenum attenuation were also observed. Bed-sediment concentration profiles collected during 2017 also indicated attenuation of uranium and molybdenum from groundwater during hyporheic mixing of surface water with the legacy plume during groundwater upwelling into the river. Streamflow measurements combined with equal discharge increment water sampling along the study reach indicated an increase in dissolved uranium concentrations in the downstream direction during 2016 and 2017. Net uranium load entering the Little Wind River study reach was about 290 and 435 grams per day during 2016 and 2017, respectively. Biological samples indicated that low levels of uranium and molybdenum exposure were confined to the benthos in the Little Wind River within and immediately downstream from the perimeter of the groundwater plume. Concentrations of molybdenum and uranium in filamentous algae were consistently low at all sites in the study reach with no indication of increased exposure of dissolved bioavailable molybdenum or uranium at sites next to or downstream from the groundwater plume.Comparison of the August 2017 results from electromagnetic induction, tube seepage meters, vertical thermal profiling, and pore-water chemistry surveys were in general agreement in identifying areas with upwelling groundwater conditions along the study reach. However, the electroconductivity values measured with electromagnetic induction in the top 100 centimeters of sediment did not agree with sodium concentrations measured in pore-water samples collected at similar streambed depths. Differences and similarities between multiple methods can result in additional insights into hydrologic and biogeochemical processes that may be occurring along a reach of a river system interacting with shallow groundwater inputs. It may be advantageous to apply a variety of geophysical, geochemical, hydrologic, and biological tools at other Uranium Mill Tailings Remedial Action (https://www.energy.gov/sites/prod/files/2014/10/f19/UMTRCA.pdf) sites during the investigation of legacy contaminant plume interactions with surface-water systems.

Long-term studies of stream ecosystems are essential for assessing restoration success because they allow researchers to quantify recovery trajectories, gauge the relative influence of episodic events, and determine the time required to achieve clean-up objectives. To quantify responses of benthic macroinvertebrate assemblages to stream remediation, we integrated results of 4 long-term (20–29 y) assessments of mining-impacted watersheds that were broadly distributed across the western US (California, Colorado, Idaho, Montana). Using a before–after control–impact (BACI) study design, we observed substantial reductions in metal concentrations and corresponding improvements of benthic assemblages following remediation. Recovery rates were relatively consistent, and streams typically recovered within 10 to 15 y after remediation was initiated (mean = 10.25 y), although episodic events changed trajectories at some sites. Differences in recovery among watersheds were likely determined by a number of factors, including the severity of contamination, effectiveness of remediation, proximity to upstream sources of colonization, and hydrologic variation. We also observed considerable variation in the rate and extent of recovery among assemblage metrics. For example, total abundance and richness recovered rapidly at most sites, but the composition of benthic macroinvertebrate assemblages remained substantially altered compared with reference sites. Using piecewise linear regression, we estimated a threshold response of Ephemeroptera, Plecoptera, and Trichoptera (EPT) species richness at ~1 cumulative criteria unit (CCU), which is the sum of the fractions of chronic water-quality criteria for metals measured, suggesting this value was protective of benthic assemblages. However, EPT richness was reduced by ~20% at 2× this CCU value, indicating that moderate exceedances of water-quality criteria could substantially affect stream biodiversity. Non-metric multidimensional scaling analyses identified common sets of species trait states across the 4 watersheds that were associated with either metal contamination or with recovering and intact reference stream assemblages. Our study illustrates the importance of long-term studies for quantifying responses to stream restoration and the usefulness of BACI designs for demonstrating cause-and-effect relationships between restoration treatments and community recovery. Because these 4 watersheds were among the most severely polluted sites in the western US, our study demonstrates the value of these investments in watershed restoration and the potential for success under the most extreme conditions.

First posted November 22, 2017 For additional information, contact: Director, Idaho Water Science Center U.S. Geological Survey 230 Collins Road Boise, Idaho 83702 The U.S. Geological Survey, in cooperation with Blaine County and The Nature Conservancy, evaluated the status of macroinvertebrate communities prior to and following a channel restoration project in Silver Creek, Blaine County, Idaho. The objective of the evaluation was to determine whether 2014 remediation efforts to restore natural channel conditions in an impounded area of Silver Creek caused declines in local macroinvertebrate communities. Starting in 2001 and ending in 2016, macroinvertebrates were sampled every 3 years at two long-term trend sites and sampled seasonally (spring, summer, and autumn) in 2013, 2015, and 2016 at seven synoptic sites. Trend-site communities were collected from natural stream-bottom substrates to represent locally established macroinvertebrate assemblages. Synoptic site communities were sampled using artificial (multi-plate) substrates to represent recently colonized (4–6 weeks) assemblages. Statistical summaries of spatial and temporal patterns in macroinvertebrate taxonomic composition at both trend and synoptic sites were completed.The potential effect of the restoration project on resident macroinvertebrate populations was determined by comparing the following community assemblage metrics:Total taxonomic richness (taxa richness);Total macroinvertebrate abundance (total abundance);Ephemeroptera, Plecoptera, Trichoptera (EPT) richness;EPT abundance;Simpson’s diversity; andSimpson’s evenness for periods prior to and following restoration.A significant decrease in one or more metric values in the period following stream channel restoration was the basis for determining impairment to the macroinvertebrate communities in Silver Creek.Comparison of pre-restoration (2001–13) and post‑restoration (2016) macroinvertebrate community composition at trend sites determined that no significant decreases occurred in any metric parameter for communities sampled in 2016. Taxa and EPT richness of colonized assemblages at synoptic sites increased significantly from pre-restoration in 2013 to post-restoration in 2015 and 2016. Similarly, total and EPT abundances at synoptic sites showed non-significant increases from 2013 to 2015 and 2016. Significant seasonal differences in macroinvertebrate assemblages were apparent at synoptic site locations and likely reflected typical life-history patterns of increased insect emergence and development in the late spring and early summer months. Taxa and EPT richness were each significantly higher in spring and summer than in autumn, and total abundances were significantly higher in spring than in summer and autumn. No significant differences in community diversity or evenness of colonized communities were noted at synoptic site locations between pre- and post-restoration years or among seasons. Select community-metric results from the trend- and synoptic‑site sampling indicated that the Silver Creek restoration effort in 2014 did not result in a significant decline in resident macroinvertebrate communities.

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This report summarizes a national assessment of the ecological health of streams done by the U.S. Geological Survey's (USGS) National Water-Quality Assessment Program (NAWQA). Healthy functioning stream ecosystems provide society with many benefits, including water purification, flood control, nutrient recycling, waste decomposition, fisheries, and aesthetics. The value to society of many of these benefits is substantial; for example, sportfishing in the United States generates an estimated annual economic output of $125 billion, including more than 1 million jobs (National Research Council, 2005; American Sportfishing Association, 2008). Continued monitoring and assessment of the Nation's streams is needed to support informed decisions that will safeguard this important natural and economic resource. The quality of streams and rivers is often assessed with measures of the chemical or physical properties of water. However, a more comprehensive perspective is obtained if resident biological communities are also assessed. Guidelines to protect human health and aquatic life have been established for specific physical and chemical properties of water and have become useful yardsticks with which to assess water quality. Biological communities provide additional crucial information because they live within streams for weeks to years and therefore integrate through time the effects of changes to their chemical or physical environment. In addition, biological communities are a direct measure of stream health—an indicator of the ability of a stream to support aquatic life. Thus, the condition of biological communities, integrated with key physical and chemical properties, provides a comprehensive assessment of stream health.

National Findings and Their ImplicationsAlthough the use of artificial fertilizer has supported increasing food production to meet the needs of a growing population, increases in nutrient loadings from agricultural and, to a lesser extent, urban sources have resulted in nutrient concentrations in many streams and parts of aquifers that exceed standards for protection of human health and (or) aquatic life, often by large margins.Do NAWQA findings substantiate national concerns for aquatic and human health?National Water-Quality Assessment (NAWQA) findings indicate that nutrient concentrations in streams and groundwater in basins with significant agricultural or urban development are substantially greater than naturally occurring or "background" levels. For example, median concentrations of total nitrogen and phosphorus in agricultural streams are about 6 times greater than background levels. Findings also indicate that concentrations in streams routinely were 2 to 10 times greater than regional nutrient criteria recommended by the U.S. Environmental Protection Agency (USEPA) to protect aquatic life. Such large differences in magnitude suggest that significant reductions in sources of nutrients, as well as greater use of land management strategies to reduce the transport of nutrients to streams, are needed to meet recommended criteria for streams draining areas with significant agricultural and urban development.Nitrate concentrations above the Federal drinking-water standard—or Maximum Contaminant Level (MCL)—of 10 milligrams per liter (mg/L, as nitrogen) are relatively uncommon in samples from streams used for drinking water or from relatively deep aquifers; the MCL is exceeded, however, in more than 20 percent of shallow (less than 100 feet below the water table) domestic wells in agricultural areas. This finding raises concerns for human health in rural agricultural areas where shallow groundwater is used for domestic supply and may warn of future contamination of deeper groundwater pumped from public‑supply wells.Are levels of nutrients in water increasing or decreasing?A decadal assessment of trends in concentrations of nitrogen and phosphorus from about 1993 to 2003 shows minimal changes in those concentrations in the majority of studied streams across the Nation, and more upward than downward trends in concentrations at sites with changes. These findings underscore the need for reductions in nutrient inputs or management strategies that would reduce transport of nutrients to streams. Upward trends were evident among all land uses, including those only minimally affected by agricultural and (or) urban development, which suggests that additional protection of some of our Nation's most pristine streams warrants consideration.The median of nitrate concentrations in groundwater from 495 wells also increased significantly from 3.2 to 3.4 mg/L (6 percent) during about the same period, and the proportion of wells with concentrations of nitrate greater than the MCL increased from 16 to 21 percent. Nitrate concentrations in water in deep aquifers are likely to increase during the next decade as shallow groundwater with elevated concentrations moves downward. The potential for future contamination of the deep aquifers requires attention because these aquifers commonly are used for public water supply, and because restoration of groundwater is costly and difficult.Long-term and consistent monitoring of nutrients, improved accounting of nutrient sources, and improved tracking and modeling of climatic and landscape changes will be essential for distinguishing trends in nutrient concentrations, understanding the causes of those trends, and accurately tracking the effectiveness of strategies implemented to manage nutrients.

Relations between tissue trace element concentrations and species traits were examined for 45 fish species to determine the extent to which trait-based characteristics accounted for relative differences among species in trace element bioaccumulation. Percentages of fish species correctly classified by discriminant analysis according to traits predicted by tissue trace element concentrations ranged from 72% to 87%. Tissue concentrations of copper, mercury, selenium, and zinc appeared to have the greatest overall influence on differentiating species according to trait characteristics. Discrimination of trait characteristics did not appear to be strongly influenced by local sources of trace elements in the streambed sediment. Bioaccumulation was greatest for those species classified as primarily detritivores, having relatively large adult body size, considered nonmigratory with respect to reproductive strategy, occurring mostly in large or variable size streams and rivers, preferring depositional areas within the stream channel, and preferring benthic rather than open-water habitats. Our findings provide evidence of the strong relationship between bioaccumulation of environmental trace elements and trait-based factors that influence contaminant exposure.

The U.S. Geological Survey National Water-Quality Assessment Program collected tissue samples from a variety of aquatic organisms during 1992-1999 within 47 study units across the United States. These tissue samples were collected to determine the occurrence and distribution of 20 major and minor trace elements in aquatic organisms. This report presents the tissue trace-element concentration data, sample summaries, and concentration statistics for 1,457 tissue samples representing 76 species or groups of fish, aquatic invertebrates, and plants were collected at 824 sampling sites.

Twenty-eight sites along the Wasatch Front, north central Utah, representing the range of urban land use intensity for wadeable streams Of the area, were sampled in September 2000. Fish communities were assessed by single-pass electrofishing, and physical habitat and water-quality characteristics were measured. Oil average, normative species comprised 54% of species richness and 53% of relative abundance, although only Salmo trutta and Pimephales promelas were very abundant at any I site. Salmo trutta mid Catostomus platyrhynchus, a native species, were the most widely distributed and abundant species captured. Analysis of fish communities using nonmetric multidimensional scaling (NMDS) revealed a community gradient from sites dominated by Salmo trutta and Cottus species (C. bairdi, C. beldingi) to sites dominated by Catostomus platyrhynchus. Sites dominated by C. platyrhynchus were smaller in size and had less habitat cover, smaller average substrate size, higher concentrations of dissolved constituents, and higher water temperature than sites dominated by S. trutta. Sites dominated by C platyrhynchus were located in more intensely urbanized watersheds at lower elevations. Stream size and associated instream habitat availability appear to limit S. trutta distribution and abundance, while native species appear more tolerant of decreased water quality, and increased water temperatures in more urbanized streams. Most of the study sites are affected by development of water infrastructure for human water use (e.g., dams and diversions), and this infrastructure may play a role in dispersal of species.

The environmental setting (e.g., climate, topography, geology) and land use affect stream physical characteristics singly and cumulatively. At broad geographic scales, we determined the importance of environmental setting and land use in explaining variation in stream physical characteristics. We hypothesized that as the spatial scale decreased from national to regional, land use would explain more of the variation in stream physical characteristics because environmental settings become more homogeneous. At a national scale, stepwise linear regression indicated that environmental setting was more important in explaining variability in stream physical characteristics. Although statistically discernible, the amount of variation explained by land use was not remarkable due to low partial correlations. At level II ecoregion spatial scales (southeastern USA plains, central USA plains, and a combination of the western Cordillera and the western interior basins and ranges), environmental setting variables were again more important predictors of stream physical characteristics, however, as the spatial scale decreased from national to regional, the portion of variability in stream physical characteristics explained by basin land use increased. Development of stream habitat indicators of land use will depend upon an understanding of relations between stream physical characteristics and environmental factors at multiple spatial scales. Smaller spatial scales will be necessary to reduce the confounding effects of variable environmental settings before the effects of land use can be reliably assessed.

Relations between stream habitat and urban land-use intensity were examined in 90 stream reaches located in or near the metropolitan areas of Salt Lake City, Utah (SLC) Birmingham, Alabama (BIR); and Boston, Massachusetts (BOS). Urban intensity was based on a multi-metric index (urban intensity index or UII) that included measures of land cover, socioeconomic organization, and urban infrastructure. Twenty-eight physical variables describing channel morphology, hydraulic properties, and streambed conditions were examined. None of the habitat variables was significantly correlated with urbanization intensity in all three study areas. Urbanization effects on stream habitat were less apparent for streams in SLC and BIR, owing to the strong influence of basin slope (SLC) and drought conditions (BIR) on local flow regimes. Streamflow in the BOS study area was not unduly influenced by similar conditions of climate and physiography, and habitat conditions in these streams were more responsive to urbanization. Urbanization in BOS contributed to higher discharge, channel deepening, and increased loading of fine-rained particles to stream channels. The modifying influence of basin slope and climate on hydrology of streams in SLC and BIR limited our ability to effectively compare habitat responses among different urban settings and identify common responses that might be of interest to restoration or water management programs. Successful application of land- use models such as the UII to compare urbanization effects on stream habitat in different environmental settings must account for inherent differences in natural and anthropogenic factors affecting stream hydrology and geomorphology The challenge to future management of urban development is to further quantify these differences by building upon existing models, and ultimately develop a broader understanding of urbanization effects oil aquatic ecosystems.

—Relations between stream habitat and urban land-use intensity were examined in 90 stream reaches located in or near the metropolitan areas of Salt Lake City, Utah (SLC); Birmingham, Alabama (BIR); and Boston, Massachusetts (BOS). Urban intensity was based on a multi-metric index (urban intensity index or UII) that included measures of land cover, socioeconomic organization, and urban infrastructure. Twenty-eight physical variables describing channel morphology, hydraulic properties, and streambed conditions were examined. None of the habitat variables was significantly correlated with urbanization intensity in all three study areas. Urbanization effects on stream habitat were less apparent for streams in SLC and BIR, owing to the strong influence of basin slope (SLC) and drought conditions (BIR) on local flow regimes. Streamflow in the BOS study area was not unduly influenced by similar conditions of climate and physiography, and habitat conditions in these streams were more responsive to urbanization. Urbanization in BOS contributed to higher discharge, channel deepening, and increased loading of fine-grained particles to stream channels. The modifying influence of basin slope and climate on hydrology of streams in SLC and BIR limited our ability to effectively compare habitat responses among different urban settings and identify common responses that might be of interest to restoration or water management programs. Successful application of land-use models such as the UII to compare urbanization effects on stream habitat in different environmental settings must account for inherent differences in natural and anthropogenic factors affecting stream hydrology and geomorphology. The challenge to future management of urban development is to further quantify these differences by building upon existing models, and ultimately develop a broader understanding of urbanization effects on aquatic ecosystems. * Corresponding author: tmshort@usgs.gov Introduction Despite the fact that urbanization represents a relatively small component of human-caused landscape change (U.S. Environmental Protection Agency 2000), urban development has a profoundly degrading influence on stream ecosystems (Grimm et al. 2000; Paul and Meyer 2001). The disproportionately large influence of urbanization on surface water systems can be attributed to dramatic changes in land surface characteristics, such as soil properties, vegetative cover, and runoff potential as impervious surface area increases,

Data collected from 20 major river basins between 1993 and 1995 as part of the US Geological Survey's (USGS) National Water-Quality Assessment (NAWQA) Program were analyzed to assess patterns in introduced and native fish species richness and abundance relative to watershed characteristics and stream physicochemistry. Sites (N=157) were divided into three regions-northeast, southeast, and west- to account for major longitudinal differences in precipitation/runoff and latitudinal limits of glaciation that affect zoogeographic patterns in fish communities. Common carp (Cyprinus carpio) and largemouth bass (Micropterus salmoides) were the most frequently collected introduced fish species across all river basins combined. Based on the percentage of introduced fish species, the fish communities most altered by the presence of introduced fish occurred in the western and northeastern parts of the US. Native fish species richness was not an indicator of introduced fish species richness for any of the three regions. However, in the west, introduced fish species richness was an indicator of total fish species richness and the abundance of introduced fish was negatively related to native fish species richness. Some relations between introduced fish species and environmental conditions were common between regions. Increased introduced fish species richness was related to increased population density in the northeast and southeast; increased total nitrogen in the northeast and west; and increased total phosphorous and water temperature in the southeast and west. These results suggest that introduced fish species tend to be associated with disturbance at large geographic scales, though specific relations may vary regionally.

Qualitative and quantitative methods to process benthic macroinvertebrate (BMI) samples have been developed and tested by the U.S. Geological Survey?s National Water Quality Laboratory Biological Group. The qualitative processing method is based on visually sorting a sample for up to 2 hours. Sorting focuses on attaining organisms that are likely to result in taxonomic identifications to lower taxonomic levels (for example, Genus or Species). Immature and damaged organisms are also sorted when they are likely to result in unique determinations. The sorted sample remnant is scanned briefly by a second person to determine if obvious taxa were missed. The quantitative processing method is based on a fixed-count approach that targets some minimum count, such as 100 or 300 organisms. Organisms are sorted from randomly selected 5.1- by 5.1-centimeter parts of a gridded subsampling frame. The sorted remnant from each sample is resorted by a second individual for at least 10 percent of the original sort time. A large-rare organism search is performed on the unsorted remnant to sort BMI taxa that were not likely represented in the sorted grids. After either qualitatively or quantitatively sorting the sample, BMIs are identified by using one of three different types of taxonomic assessment. The Standard Taxonomic Assessment is comparable to the U.S. Environmental Protection Agency Rapid Bioassessment Protocol III and typically provides Genus- or Species-level taxonomic resolution. The Rapid Taxonomic Assessment is comparable to the U.S. Environmental Protection Agency Rapid Bioassessment Protocol II and provides Familylevel and higher taxonomic resolution. The Custom Taxonomic Assessment provides Species-level resolution whenever possible for groups identified to higher taxonomic levels by using the Standard Taxonomic Assessment. The consistent use of standardized designations and notes facilitates the interpretation of BMI data within and among water-quality studies. Taxonomic identifications are quality assured by verifying all referenced taxa and randomly reviewing 10 percent of the taxonomic identifications performed weekly by Biological Group taxonomists. Taxonomic errors discovered during this review are corrected. BMI data are reviewed for accuracy and completeness prior to release. BMI data are released phylogenetically in spreadsheet format and unprocessed abundances are corrected for laboratory and field subsampling when necessary.

Four studies were done in the upper Merced River drainage in Yosemite National Park and nearby areas from 1993 to 1996. First, monitoring studies of benthic algae, benthic invertebrates, fish, and habitat were undertaken at sites near Happy Isles and Pohono bridges from 1993 to 1995 as part of the National Water-Quality Assessment Program of the U.S. Geological Survey. Second, an ecological survey of benthic algae, benthic invertebrates, fish, and habitat was done in the upper Merced River drainage in 1994. Third, a special study of benthic algae, habitat, and water quality was done in the reach of the Merced River within Yosemite Valley to deter-mine whether human activities were having measurable effects on the ecosystem. Fourth, baseline data on benthic algae, benthic invertebrates, and habitat were collected in 1996 at four sites, two of which were undergoing extensive streambank restoration activities. Comparisons of the baseline data with future collections could be used to assess the effects of streambank restoration on aquatic biota. The general conclusion from these studies is that water quality in the upper Merced River was very good from 1993-1996, despite high levels of human activities in some areas. Fish communities did not appear to be a useful indicator of habitat and water quality because of low species richness and the apparent importance of physical barriers in determining species distributions. Measurements of fish densities and size-distributions might be useful, but would be logistically difficult. Benthic algae and benthic invertebrates do appear to be useful in monitoring environmental conditions. Benthic algae may be more sensitive than benthic invertebrates to small environmental differences within years. Benthic algae were also more responsive than benthic invertebrates to differences in discharge between years. Thus, benthic invertebrates may be more useful in comparing environmental conditions between years, independent of discharge conditions.

We examined mercury concentration in muscle of walleye Stizostedion vitreum from three reaches in Franklin D. Roosevelt Lake, a reservoir on the Columbia River, and from the upper Columbia River, an area contaminated by wastes from metal mining and associated processing activities. Our objectives were to describe the relation between size and age of walleyes and tissue concentrations of mercury and to compare mercury concentrations within a single reservoir system among spatially segregated cohorts. Overall, mercury concentrations in walleye muscle ranged from 0.11 to 0.44 mg/kg (wet weight) and were positively correlated with age, weight, and length of the fish. Mercury concentrations in walleyes varied spatially within the system; the highest concentrations were in fish from the lower and middle reaches of the reservoir. Condition factor of age-2+ fish was inversely related to tissue concentration of mercury and was lower in fish from the lower and middle reaches than in fish from the upper reach. Spatial patterns in condition factor and mercury in walleyes were unrelated to concentrations of total mercury in surficial bed sediments, which ranged from less than 0.05 to 2.8 mg/kg (dry weight). We suggest that the observed spatial differences in the concentrations of mercury in walleyes may be attributed to the fish preferring to spawn and forage in specific areas where the bioavailability of mercury varies due to local differences in the physical and chemical environment.