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USGS2025

Hydrologic variability and groundwater age of springs in eastern Oregon and northern Nevada, USA

The ecological importance of springs in semiarid regions is far greater than their small size and sparse distribution, yet little is known about the hydrologic functioning of these systems. During 2016–22, 261 springs were visited in the volcanic terrane of eastern Oregon and northern Nevada. When conditions were suitable, measurements of discharge, water temperature, and specific conductance were made, and samples for the analysis of carbon-14, tritium, and water stable isotopes (WSI) were collected. A subset of 60 springs was revisited during different seasons in the same year and during the dry season in multiple years to evaluate variability in discharge, chemistry, and groundwater age. Specific conductance and WSI varied considerably among springs across the study area but were unexpectedly stable across seasons and years at individual springs. Seasonal and interannual variability in spring discharge was related to the residence time of the discharging groundwater. Springs discharging older groundwater (10 3 –10 4 years) had significantly less variability in their discharge compared to springs discharging younger groundwater (10 0 –10 1 years). Variability among springs discharging younger groundwater included cessation of late-summer discharge at 18 % of the repeat-visit springs. A logistic regression model predicted the age of discharging spring water with 89 % accuracy using only the spring latitude, longitude, elevation, and δ 2 H value. This study framework provides a simple, inexpensive, and robust method to provisionally assess the hydrologic behavior of springs having little or no prior information in understudied, semiarid regions across the globe.

Nevada, Oregon↗

USGS2011

Diel biogeochemical processes and their effect on the aqueous chemistry of streams: A review

This review summarizes biogeochemical processes that operate on diel, or 24-h, time scales in streams and the changes in aqueous chemistry that are associated with these processes. Some biogeochemical processes, such as those producing diel cycles of dissolved O 2 and pH, were the first to be studied, whereas processes producing diel concentration cycles of a broader spectrum of chemical species including dissolved gases, dissolved inorganic and organic carbon, trace elements, nutrients, stable isotopes, and suspended particles have received attention only more recently. Diel biogeochemical cycles are interrelated because the cyclical variations produced by one biogeochemical process commonly affect another. Thus, understanding biogeochemical cycling is essential not only for guiding collection and interpretation of water-quality data but also for geochemical and ecological studies of streams. Expanded knowledge of diel biogeochemical cycling will improve understanding of how natural aquatic environments function and thus lead to better predictions of how stream ecosystems might react to changing conditions of contaminant loading, eutrophication, climate change, drought, industrialization, development, and other factors.

Chemical Geology↗

USGS1989

Terrestrial population models for ecological risk assessment: A state-of-the-art review

Few attempts have been made to formulate models for predicting impacts of xenobiotic chemicals on wildlife populations. However, considerable effort has been invested in wildlife optimal exploitation models. Because death from intoxication has a similar effect on population dynamics as death by harvesting, these management models are applicable to ecological risk assessment. An underlying Leslie-matrix bookkeeping formulation is widely applicable to vertebrate wildlife populations. Unfortunately, however, the various submodels that track birth, death, and dispersal rates as functions of the physical, chemical, and biotic environment are by their nature almost inevitably highly species- and locale-specific. Short-term prediction of one-time chemical applications requires only information on mortality before and after contamination. In such cases a simple matrix formulation may be adequate for risk assessment. But generally, risk must be projected over periods of a generation or more. This precludes generic protocols for risk assessment and also the ready and inexpensive predictions of a chemical's influence on a given population. When designing and applying models for ecological risk assessment at the population level, the endpoints (output) of concern must be carefully and rigorously defined. The most easily accessible and appropriate endpoints are (1) pseudoextinction (the frequency or probability of a population falling below a prespecified density), and (2) temporal mean population density. Spatial and temporal extent of predicted changes must be clearly specified a priori to avoid apparent contradictions and confusion.

Environmental Toxicology and Chemistry↗

USGS2021

Regional target loads of atmospheric nitrogen and sulfur deposition for the protection of stream and watershed soil resources of the Adirondack Mountains, USA

Acidic deposition contributes to a range of environmental impacts across forested landscapes, including acidification of soil and drainage water, toxic aluminum mobilization, depletion of available soil nutrient cations, and impacts to forest and aquatic species health and biodiversity. In response to decreasing levels of acidic deposition, soils and drainage waters in some regions of North America have become gradually less acidic. Thresholds of atmospheric deposition at which adverse ecological effects are manifested are called critical loads (CLs) and/or target loads (TLs). Target loads are developed based on approaches that account for spatial and temporal aspects of acidification and recovery. Exceedance represents the extent to which current or projected future levels of acidic deposition exceed the level expected to cause ecological harm. We report TLs of sulfur (S) and nitrogen (N) deposition and the potential for ecosystem recovery of watershed soils and streams in the Adirondack region of New York State, resources that have been less thoroughly investigated than lakes. Regional TLs were calculated by statistical extrapolation of hindcast and forecast simulations of 25 watersheds using the process-based model PnET-BGC coupled with empirical observations of stream hydrology and established sensitivity of sugar maple ( Acer saccharum ) to soil base saturation and brook trout ( Salvelinus fontinalis ) to stream acid neutralizing capacity (ANC). Historical impacts and the expected recovery timeline of regional soil and stream chemistry and fish community condition within the Adirondack Park were evaluated. Analysis suggests that many low-order Adirondack streams and associated watershed soils have low TLs (<40 meq/m 2 /yr of N+S deposition) to achieve specified benchmarks for recovery of soil base saturation or stream ANC. Acid-sensitive headwater and low-order streams and watershed soils in the region are expected to experience continued adverse effects from N and S deposition well into the future even under aggressive emissions reductions. Watershed soils and streams in the western Adirondack Park are particularly vulnerable to acidic deposition and currently in exceedance of TLs. The methods used for linking statistical and process-based models to consider chemical and biological response under varying flow conditions at the regional scale in this study can be applied to other areas of concern.

New York↗

USGS2007

Effects of methylmercury exposure on the immune function of juvenile common loons (Gavia immer)

We conducted a dose-response laboratory study to quantify the level of exposure to dietary Hg, delivered as methylmercury chloride (CH3HgCl), that is associated with suppressed immune function in captive-reared common loon (Gavia immer) chicks. We used the phytohemagglutinin (PHA) skin test to assess T-lymphocyte function and the sheep red blood cell (SRBC) hemagglutination test to measure antibody-mediated immunity. The PHA stimulation index among chicks receiving dietary Hg treatment did not differ significantly from those of chicks on the control diet (p = 0.15). Total antibody (immunoglobulin [Ig] M [primary antibody] + IgG [secondary response]) production to the SRBC antigen in chicks treated with dietary methylmercury (MeHg), however, was suppressed (p = 0.04) relative to chicks on control diets. Analysis indicated suppression of total Ig production (p = 0.025 with comparisonwise ?? level = 0.017) between control and 0.4 ??g Hg/g wet food intake treatment groups. Furthermore, the control group exhibited a higher degree of variability in antibody response compared to the Hg groups, suggesting that in addition to reducing the mean response, Hg treatment reduced the normal variation attributable to other biological factors. We observed bursal lymphoid depletion in chicks receiving the 1.2 ??g Hg/g treatment (p = 0.017) and a marginally significant effect (p = 0.025) in chicks receiving the 0.4 ??g Hg/g diet. These findings suggest that common loon chick immune systems may be compromised at an ecologically relevant dietary exposure concentration (0.4 ??g Hg/g wet wt food intake). We also found that chicks hatched from eggs collected from low-pH lakes exhibited higher levels of lymphoid depletion in bursa tissue relative to chicks hatched from eggs collected from neutral-pH lakes. ?? 2007 SETAC.

Environmental Toxicology and Chemistry↗

USGS2009

DayCent-Chem simulations of ecological and biogeochemical processes of eight mountain ecosystems in the United States

Atmospheric deposition of nitrogen (N) and sulfur (S) cause complex responses in ecosystems, from fertilization to forest ecosystem decline, freshwater eutrophication to acidification, loss of soil base cations, and alterations of disturbance regimes. DayCent-Chem, an ecosystem simulation model that combines ecosystem nutrient cycling and plant dynamics with aqueous geochemical equilibrium calculations, was developed to address ecosystem responses to combined atmospheric N and S deposition. It is unique among geochemically-based models in its dynamic biological cycling of N and its daily timestep for investigating ecosystem and surface water chemical response to episodic events. The model was applied to eight mountainous watersheds in the United States. The sites represent a gradient of N deposition across locales, from relatively pristine to N-saturated, and a variety of ecosystem types and climates. Overall, the model performed best in predicting stream chemistry for snowmelt-dominated sites. It was more difficult to predict daily stream chemistry for watersheds with deep soils, high amounts of atmospheric deposition, and a large degree of spatial heterogeneity. DayCent-Chem did well in representing plant and soil carbon and nitrogen pools and fluxes. Modeled stream nitrate (NO 3 - ) and ammonium (NH 4 + ) concentrations compared well with measurements at all sites, with few exceptions. Simulated daily stream sulfate (SO 4 2- ) concentrations compared well to measured values for sites where SO 4 2- deposition has been low and where SO 4 2- adsorption/desorption reactions did not seem to be important. The concentrations of base cations and silica in streams are highly dependent on the geochemistry and weathering rates of minerals in each catchment, yet these were rarely, if ever, known. Thus, DayCent-Chem could not accurately predict weathering products for some catchments. Additionally, few data were available for exchangeable soil cations or the magnitude of base cation deposition as a result of dry and fog inputs. The uncertainties related to weathering reactions, deposition, soil cation exchange capacity, and groundwater contributions influenced how well the simulated acid neutralizing capacity (ANC) and pH estimates compared to observed values. Daily discharge was well represented by the model for most sites. The chapters of this report describe the parameterization for each site and summarize model results for ecosystem variables, stream discharge, and stream chemistry. This intersite comparison exercise provided insight about important and possibly not well understood processes.

Scientific Investigations Report↗

USGS2025

Evaluating per- and polyfluoroalkyl substance (PFAS) prevalence and potential for biological effects in Lake Superior tributaries

Several per- and polyfluoroalkyl substances (PFAS) are Great Lakes binational chemicals of mutual concern. Although known to be persistent, data gaps regarding PFAS prevalence and biological effects exist, especially within Lake Superior’s watershed. In this 2022 study of 27 United States tributaries to Lake Superior, water samples were collected during spring runoff, summer baseflow, and fall baseflow, and stream bed-sediment samples were collected during fall. PFAS were detected in 97% of water samples and 59% of sediment samples. Summed PFAS water sample concentrations (33 analytes) were generally low relative to other environmental studies (median = 6.5 ng/L), except at Newton, Miller, and Sargent Creeks (up to 391 ng/L). Maximum water concentrations were from perfluorooctane sulfonic acid (PFOS) and perfluorohexane sulfonate (PFHxS); perfluorobutanoic acid (PFBA) had the greatest median concentration. PFBA and perfluorooctanoic acid (PFOA) were most frequently detected in water samples (>90%). Summed PFAS sediment sample concentrations (33 analytes) were also generally low (median = 19 ng/kg), except at Newton and Muggun Creeks (up to 797 ng/kg). In sediment, PFOS occurred most frequently and had the greatest concentrations. The most contaminated samples came from sites with documented aqueous film forming foam or wastewater contamination; summer baseflow samples exhibited elevated PFAS concentrations. Comparison of observed water concentrations to published and derived water-quality guidelines indicated PFOS and PFHxS pose the greatest potential ecological risks. Observed PFAS mixtures may affect lipid metabolism, growth, thyroid hormones, and survival of aquatic organisms. The observed concentrations and predicted biological effects are likely underestimates of the environmental impact of PFAS. Despite low anthropogenic influence in Lake Superior’s watershed, PFAS were ubiquitous and occurred at potentially harmful concentrations.

Michigan, Minnesota, Wisconsin↗

USGS2020

Assessment of methods for soil monitoring in the Adirondack region of New York

Repeated sampling to detect changes in forest soils was rarely used before 1990, but the value of soil monitoring in understanding environmental change is becoming well established. The growing number of resampling studies has shown that sampling designs and procedures must be adapted to the objectives of the monitoring program and the soils being monitored. In the Adirondack region, current priorities include the response of soils to large increases, and more recently, large decreases in acidic deposition, and changes driven by trending climate such as altered pools of soil organic carbon, as well as other unforeseen factors that will occur in the future. To improve methods and assess the feasibility of long-term soil monitoring in the Adirondack region, the United States Geological Survey (USGS) conducted a pilot project to evaluate a new sampling method for characterizing soils on a watershed basis. Results obtained with this new approach, referred to as the ADK sampling method, was compared to methods used in previous sampling conducted in 2004 as part of the Western Adirondack Stream Survey (WASS), and also to previous high-replication pit sampling in the North and South Tributary watersheds of Buck Creek (North Buck and South Buck). The number of sampling locations and spatial distribution of sampling points within watersheds differed among the methods, although pit excavation was used to obtain samples in all cases. In addition, this investigation evaluated the use of small diameter corers as a means to measure forest floor mass with greater accuracy and precision than commonly used methods such as pit excavation. Sufficient statistical power to detect ecologically relevant changes in upper profile horizons (Oe, Oa and upper 10 cm of the B) were achieved with the ADK sampling method that utilized 18 pit excavations per watershed. The sampling locations were organized within each watershed into three study areas (six sampling locations per study area) that represented the primary types of landscape within the watershed. Sampling at 18 locations per watershed was found to be nearly as effective at detecting changes as sampling at 28 locations per watershed. Numerous significant changes (P < 0.10) were detected with both 18 and 28 sampling locations at sampling intervals of 12 to 16 years. The relationship between soil data obtained with the ADK method and stream chemistry at the base of the watershed suggested that this approach adequately characterized soil variability within the watershed for the purpose of studying soil-stream linkages. Significant changes in upper B horizon calcium (P < 0.10) and Oa horizon aluminum (P < 0.01) were detected when the data from the four WASS watersheds were combined with the two Buck Creek watersheds, which suggested that there would be value in resampling other WASS watersheds previously sampled in 2004 to support a regional assessment. Study results support small diameter cores as a useful method to monitor changes in the organic matter mass of the forest floor. This method showed high reproducibility in repeated sampling tests and lower spatial variability in sample data than traditional approaches when compared on a watershed basis. Soil coring is also faster and requires less equipment than pit excavation methods, which makes it more conducive to sampling over large areas. However, organic matter mass of the forest floor determined by coring was consistently less than the values obtained by the ADK sampling method that used pit sampling and vertical horizon measurements, and also literature values of a previous Adirondack study that utilized pit sampling in which the entire horizon was collected over a measured area. However, a high correlation (R2 = 0.87) occurred between organic matter content (expressed as Mg ha-1) determined by coring and the ADK sampling method. Differing methods with regard to where sample could be collected, and how organic matter was collected for chemical analysis were the likely reasons for differences in quantification of forest floor organic mass. Collection of forest floor cores in conjunction with the ADK method is recommended to provide improved sensitivity in detecting changes in the forest floor in proximity of where full analyses of the soil profile are being done. This duel sampling approach represents an optimized method for measuring and understanding how Adirondack soils will change in the future.

New York↗

USGS2017

Biological relevance of streamflow metrics: Regional and national perspectives

Protecting the health of streams and rivers requires identifying ecologically significant attributes of the natural flow regime. Streamflow regimes are routinely quantified using a plethora of hydrologic metrics (HMs), most of which have unknown relevance to biological communities. At regional and national scales, we evaluated which of 509 commonly used HMs were associated with biological indicators of fish and invertebrate community integrity. We quantified alteration of each HM by using statistical models to predict site-specific natural baseline values for each of 728 sites across the USA where streamflow monitoring data were available concurrent with assessments of invertebrate or fish community integrity. We then ranked HMs according to their individual association with biological integrity based on random forest models that included HMs and other relevant covariates, such as land cover and stream chemistry. HMs were generally the most important predictors of biological integrity relative to the covariates. At a national scale, the most influential HMs were measures of depleted high flows, homogenization of flows, and erratic flows. Unique combinations of biologically relevant HMs were apparent among regions. We discuss the implications of our findings to the challenge of selecting HMs for streamflow research and management.

Freshwater Science↗

USGS2021

Insect-mediated contaminant flux at the land–water interface: Are ecological subsidies driving exposure or is exposure driving subsidies?

Chemical contamination of freshwaters is a global problem. In the United States alone, millions of kilometers of rivers and hectares of lakes and wetlands are impaired from contamination by chemicals including mercury, pesticides, polychlorinated biphenyls (PCBs), and trace metals (US Environmental Protection Agency, 2017 ). Efforts to mitigate the risks of contamination have largely focused on aquatic endpoints. However, these contaminants pose a risk not only to life in freshwater ecosystems but also to the terrestrial organisms that depend on freshwater ecosystems for food.

Environmental Toxicology and Chemistry↗

USGS2017

Ecology of the macrophyte Podostemum ceratophyllum Michx. (Hornleaf riverweed), a widespread foundation species of eastern North American rivers

Podostemum ceratophyllum , commonly called Hornleaf Riverweed, occurs in mid-order montane and piedmont rivers of eastern North America, where the plant grows submerged and attached to rocks and stable substrates in swift, aerated water. Multiple studies, mostly conducted in the southern portions of the plant’s range, have shown that Podostemum can variously influence benthic communities in flowing waters. However, a synthetic review of the biology and ecology of the plant is needed to inform conservation, particularly because P. ceratophyllum is reported to be in decline in much of its range, for mostly unknown reasons. We have thus summarized the literature showing that Podostemum provides substantial habitat for invertebrates and fish, may be consumed by invertebrates, turtles, and other vertebrates, removes and sequesters dissolved elements (i.e., nitrogen, phosphorus, calcium, zinc, etc.) from the water column, and contributes organic matter to the detrital pool. Podostemum may be tolerant to some forms of pollution but appears vulnerable to sedimentation, epiphytic over-growth, and hydrologic changes that result in desiccation, and possibly increased herbivory pressure. Much remains unknown about Podostemum , including aspects of morphological variation, seed dispersal, and tolerance to changes in temperature and water chemistry. Nonetheless, Podostemum may be considered a foundation species, whose loss from eastern North American rivers is likely to affect higher trophic levels and ecosystem processes.

Aquatic Botany↗

USGS1996

Episodic acidification of small streams in the northeastern United states: Effects on fish populations

As part of the Episodic Response Project (ERP), we studied the effects of episodic acidification on fish in 13 small streams in the northeastern United States: four streams in the Adirondack region of New York, four streams in the Catskills, New York, and five streams in the northern Appalachian Plateau, Pennsylvania. In situ bioassays with brook trout (Salvelinus fontinalis) and a forage fish species (blacknose dace (Rhinichthys atratulus), mottled sculpin (Cottus bairdi), or slimy sculpin (Cottus cognatus), depending on the region) measured direct toxicity. Movements of individual brook trout, in relation to stream chemistry, were monitored using radiotelemetry. Electrofishing surveys assessed fish community status and the density and biomass of brook trout in each stream. During low flow, all streams except one had chemical conditions considered suitable for the survival and reproduction of most fish species (median pH 6.0-7.2 during low flow; inorganic Al < 60 μg/L). ERP streams with suitable conditions during low flow, but moderate-to-severe episodic acidification during high flow, had higher fish mortality in bioassays, net down-stream movement of brook trout during events, and lower brook trout density and biomass compared to nonacidic streams, and lacked acid-sensitive fish species (blacknose dace and sculpin). Movement of trout into refugia (areas with higher pH and lower Al) during episodes partially mitigated the adverse effects of episodes. Recolonization from alkaline tributaries or microhabitats can maintain low densities of fish in streams that experience severe acidic episodes, but it is not sufficient to sustain fish densities and community composition at levels expected in the absence of these episodes. Fish responses to acid-base chemistry were fairly consistent across regions. In general, trout abundance was reduced and acid-sensitive fish species were absent from ERP streams with median pH < 5.0-5.2 during high flow and inorganic Al > 100-200 μg/L. We conclude that episodic acidification can have long-term effects on fish communities in small streams.

Ecological Applications↗

USGS2014

Legacy data for a northern prairie grassland: Woodworth Study Area, North Dakota, 1963-89

Ecological data commonly become more valuable through time. Such legacy data provide baseline records of past biological, physical, and social information that provide historical perspective and are necessary for assessment of stasis or change. Legacy data collected at the Woodworth Study Area (WSA), a contiguous block of grasslands, croplands, and wetlands covering more than 1,000 hectares of the Prairie Pothole Region of North Dakota, are cataloged and summarized in this study. The WSA is one of the longest researched grassland sites in the Upper Midwest. It has an extensive history of settlement, land use, and management that provides a deeper context for future research. The WSA data include long-term vegetation transect records, land use history, habitat management records, geologic information, wetland hydrology and chemistry information, and spatial images. Substantial parts of these data have not been previously reported. The WSA is representative of many other lands purchased by the U.S. Fish and Wildlife Service in the Prairie Pothole Region from the 1930s to the 1970s; therefore, synthesized data from the WSA are broadly applicable to topics of concern in northern grasslands, such as increases in non-native plants, managing for biodiversity, and long-term effects of habitat management. New techniques are also described that were used to preserve these data for future analyses. The data preservation techniques are applicable to any project with data that should be preserved for 100 years or more.

North Dakota↗

USGS2008

Changes in stream chemistry and biology in response to reduced levels of acid deposition during 1987-2003 in the Neversink River Basin, Catskill Mountains

Atmospheric acid deposition has decreased in the northeastern United States since the 1970s, resulting in modest increases in pH, acid-neutralizing capacity (ANC), and decreases in inorganic monomeric aluminum (AlIM) concentrations since stream chemistry monitoring began in the 1980s in the acid-sensitive upper Neversink River basin in the Catskill Mountains of New York. Stream pH has increased by 0.01 units/year during 1987-2003 at three sites in the Neversink basin as determined by Seasonal Kendall trend analysis. In light of this observed decrease in stream acidity, we sampled 12 stream sites within the Neversink River watershed for water chemistry, macroinvertebrates, fish, and periphytic diatoms in 2003 to compare with a similar data set collected in 1987. Metrics and indices that reflect sensitivity to stream acidity were developed with these biological data to determine whether changes in stream biota over the intervening 16 years parallel those of stream chemistry. Statistical comparisons of data on stream chemistry and an acid biological assessment profile (Acid BAP) derived from invertebrate data showed no significant differences between the two years. For pH and ANC, however, values in 2003 were generally lower than those in 1987; this difference likely resulted from higher streamflow in summer 2003. Despite these likely flow-induced changes in summer 2003, an ordination and cluster analysis of macroinvertebrate taxa based on the Acid BAP indicated that the most acidic sites in the upstream half of the East Branch Neversink River form a statistically significant separate cluster consistent with less acidic stream conditions. This analysis is consistent with limited recovery of invertebrate species in the most acidic reaches of the river, but will require additional improvement in stream chemistry before a stronger conclusion can be drawn. Data on the fish and periphytic diatom communities in 2003 indicate that slimy sculpin had not extended their habitat to upstream reaches that previously were devoid of this acid-intolerant species in 1987; a diatom acid-tolerance index indicates continued high-acid impact throughout most of the East Branch and headwaters of the West Branch Neversink River. ?? 2007 Elsevier Ltd. All rights reserved.

Ecological Indicators↗

USGS2009

Effect of agricultural practices on hydrology and water chemistry in a small irrigated catchment, Yakima River Basin, Washington

The role of irrigation and artificial drainage in the hydrologic cycle and the transport of solutes in a small agricultural catchment in central Washington's Yakima Valley were explored using hydrologic, chemical, isotopic, age-dating, and mineralogical data from several environmental compartments, including stream water, ground water, overland flow, and streambed pore water. A conceptual understanding of catchment hydrology and solute transport was developed and an inverse end-member mixing analysis was used to further explore the effects of agriculture in this small catchment. The median concentrations of major solutes and nitrates were similar for the single field site and for the catchment outflow site, indicating that the net effects of transport processes for these constituents were similar at both scales. However, concentrations of nutrients were different at the two sites, suggesting that field-scale variations in agricultural practices as well as nearstream and instream biochemical processes are important components of agricultural chemical transformation and transport in this catchment. This work indicates that irrigation coupled with artificial drainage networks may exacerbate the ecological effects of agricultural runoff by increasing direct connectivity between fields and streams and minimizing potentially mitigating effects (denitrification and dilution, for example) of longer subsurface pathways.

Washington↗

USGS2024

An introduction to Criteria for Reporting and Evaluating Exposure Datasets (CREED) for use in environmental assessments

Risks posed by environmental exposure to chemicals are routinely assessed to inform activities ranging from environmental status reporting to authorization and registration of chemicals for commercial uses. Environmental risk assessment generally relies on two key values generated from exposure data and ecotoxicity data. Data sets of measured concentrations of chemicals in environmental matrices, referred to here as exposure data, are widely used to support environmental risk management, decision-making, and reporting, such as for chemical screening, ecological or human health risk assessments, and establishment of guidelines. Practitioners have developed schemes to determine the suitability of ecotoxicity data for specific purposes, focused on evaluating reliability and relevance, but analogous schemes are not available for exposure data. Moreover, regulatory guidance arguably provides less resolution on reporting and evaluating exposure data sets compared to ecotoxicity data. The evaluation of exposure data sets is subject to limitations from variable or unreported data quality objectives and/or from differences in expert judgments, potentially introducing bias and leading to decisions based on flawed and/or inconsistent information. Exposure data sets should be evaluated for reliability and relevance prior to use in environmental assessments. This paper is the first of a four-paper series detailing the outcomes of a Society of Environmental Toxicology and Chemistry technical workshop that has developed Criteria for Reporting and Evaluating Exposure Datasets (CREED). The workshop participants developed practical, systematic criteria for consistent and transparent evaluation of the reliability (quality) and relevance (fitness for purpose) of exposure data. This guidance should apply to many different (unspecified) purposes of assessment. CREED can be used to evaluate existing data sets, but can also inform data generators interested in improving their data collection and reporting to maximize data utility to other users. This first paper details existing frameworks for the evaluation of exposure data sets and demonstrates the need for CREED, drawing from different regulatory assessments, and describes the technical workshop.

Integrated Environmental Assessment and Management↗

USGS2020

Spatial and temporal patterns in streamflow, water chemistry, and aquatic macroinvertebrates of selected streams in Fairfax County, Virginia, 2007–18

Urbanization substantially alters the landscape in ways that can impact stream hydrology, water chemistry, and the health of aquatic communities. Stormwater best management practices (BMPs) are the primary tools used to mitigate the effects of urban stressors such as increased runoff, decreased baseflow, and increased nutrient and sediment transport. To date, Fairfax County Virginia’s stormwater management program has made substantial investments into the implementation of both structural and nonstructural BMPs aimed at restoring and protecting watersheds. The U.S. Geological Survey (USGS), in cooperation with Fairfax County, Virginia, established a long-term water-resources monitoring program to evaluate the watershed-scale effects of these investments. Monitoring began at 14 stations in 2007 and was expanded to 20 stations in 2013. This report utilized the first 10 years of data collection to (1) assess water quantity and quality, as well as ecological condition; (2) compute annual nutrient and sediment loads; and (3) evaluate trends in streamflow, water quality, and ecological condition. Efforts are underway to link the biotic and abiotic patterns described herein to watershed management practices as well as factors such as land use change, public works infrastructure, and climate. Hydrologic, chemical, and benthic macroinvertebrate community conditions in the streams monitored were similar to those observed in other studies of urban streams. Multidecadal trends in baseflow indices and runoff ratios at long-term Chesapeake Bay Non-tidal Network streamgages (CB-NTN) indicate a decrease in groundwater recharge and increase in storm runoff as a result of urbanization. Streamflow yields varied spatially with land cover, geology, and soil characteristics, whereas flashiness was positively related to impervious area. Dissolved oxygen typically was lowest in the Coastal Plain and across all Triassic Lowlands streams, and highest in the Piedmont. Dissolved oxygen concentrations generally were above Virginia’s minimum criterion of 4.0 milligrams per liter (mg/L), most violations occurred at Paul Spring Branch in the Coastal Plain during the warmest months of the year owing to increased chemical and biological oxygen demand. Typical pH values of the monitored streams centered on neutrality (pH = 7); however, diurnal fluctuations were most prevalent in the continuous pH data at Flatlick Branch (FLAT; a Triassic Lowlands station), as a result of increased photosynthesis catalyzed by phosphorus-rich geology. Specific conductance (SC) varied spatially owing to geology (highest at Triassic Lowlands stations) and anthropogenic disturbance (watersheds with high impervious land cover). Specific conductance typically was inversely related to streamflow except in winter months following deicing road salt applications, when values increased by several orders of magnitude. A significant increase in SC of about 2 percent per year was observed from the combined trend result of all monitoring stations over the 10-year period. Significant SC increases occurred at nearly all monitoring stations. Increasing trends were observed during winter and nonwinter months, which suggests that salts applied to deice roadways and other impervious surfaces are stored in the environment and released year-round. Suspended-sediment (SS) concentrations in monthly samples did not vary significantly between most stations, but typically were highest in the spring and lowest in the fall as a result of seasonal differences in streamflow and climate. Suspended-sediment yields ranged from 62 to 1,428 tons per square mile (ton/mi 2 ), with a median of 302 ton/mi 2 . Annual loads were greatest during the wettest water years (October 1-September 30; 2008, 2011, and 2014), with the greatest interannual variability occurring at Difficult Run above Fox Lake (DIFF) and South Fork Little Difficult Run (SFLIL). Suspended sediment was primarily composed of silts and clays; however, the proportion of sand in suspended sediment was related positively to streamflow. Cross-correlation analyses suggested the dominant sources of SS were streambank erosion and resuspension of in-channel material at DIFF and FLAT; whereas, upland sources and erosion of upper streambanks were more common at Dead Run (DEAD), Long Branch (LONG), and SFLIL. Median total phosphorus (TP) concentrations ranged from 0.016 to 0.077 mg/L, with a networkwide median of 0.022 mg/L, were highest in the warm season (April-September), and were composed primarily of dissolved phosphorous. Although TP concentrations were relatively low across the network, the highest concentrations were consistently at stations located in the Triassic Lowlands, owing to phosphorous-rich geology, and in the Coastal Plain, owing to the low-phosphorous sorptive capacity of those soils. A significant increase in TP concentration occurred in a few stations, but the combined trend results from all stations demonstrated a significant increase of about 4 percent per year. Networkwide increases were also observed in total dissolved phosphorus, orthophosphate, and total particulate phosphorus. The composition of TP shifted from dissolved to particulate as streamflow increased and for this reason loads primarily were composed of particulate phosphorous. Median annual TP loads were highest at FLAT and DEAD and ranged from 247 to 642 pounds per square mile (lbs/mi 2 ) networkwide. Interannual variability in phosphorous yields was apparent at most stations; the highest loading years were also the wettest years during the study period and coincident with the highest peak annual flows. Total nitrogen (TN) concentrations typically were low throughout the network with exceptions occurring at stations located in watersheds with a high density of septic infrastructure. Elevated TN concentrations also were observed in some watersheds without a high density of septic systems and may be attributable to geologic and soil properties that limit denitrification as well as other unknown anthropogenic inputs. Total nitrogen typically was dominated by nitrate during baseflows; however, the proportion of particulate nitrogen increased during stormflows. Total nitrogen yields were similar across stations, with medians ranging from about 3,600 to 6,300 lbs/mi 2 and were related to annual streamflow volume. Total nitrogen concentrations and flow-normalized concentrations decreased over the 10-year period at 7 stations, with median reductions of about 2.5 percent. Increasing trends were observed at the two stations with the highest median TN concentration (Captain Hickory Run and SFLIL, 3–5 mg/L), both watersheds contain a high density of septic infrastructure. The combined trend results from all stations revealed no trend in TN and a declining trend in nitrate of about 2 percent per year. Overall, benthic community metrics indicated that streams throughout Fairfax County were initially of poor health; however, many metrics show an improving trend (from poor to fair based on the Fairfax County Index of Biological Integrity [IBI]). Significant increasing trends in IBI occurred at the network-scale and at 4 individual stations; additionally, scores improved by at least 1 qualitative category (for example, poor to fair, fair to good) at 11 of the 14 stations between 2009 (the first year all 14 stations were sampled) and 2017. Changes in all metrics suggest that the biodiversity, function, and condition of streams in Fairfax County are improving, but some of these improvements are driven by increased diversity and percent composition of organisms that are tolerant of the urban environment.

Virginia↗

USGS2015

Response of Schoenoplectus acutus and Schoenoplectus californicus at different life-history stages to hydrologic regime

For wetland restoration success to be maximized, restoration managers need better information regarding how the frequency, depth, and duration of flooding affect soil chemistry and the survival, growth, and morphology of targeted plant species. In a greenhouse study we investigated the impact of four different flooding durations (0 %, 40 %, 60 %, and 100 %) on soil physicochemistry and the responses of seedlings and adults of two species of emergent wetland macrophytes commonly used in restoration efforts ( Schoenoplectus acutus and Schoenoplectus californicus ). The longest flooding duration, which created more reducing soil conditions, resulted in significantly reduced survival of S. acutus adults (34 ± 21 % survival) and complete mortality of seedlings of both species. Schoenoplectus californicus adults exhibited higher flooding tolerance, showing little impact of flooding on morphology and physiology. A companion field study indicated that S. californicus maintained stem strength regardless of flooding duration or depth, supporting the greenhouse study results. This information serves to improve our understanding of the ecological differences between these species as well as provide restoration managers with better guidelines for targeted elevation and hydrologic regimes for these species in order to enhance the success of restoration plantings and better predict restoration site development.

Wetlands↗