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Barbara Mahler

Publications and source records attributed to Barbara Mahler.

At least 19 recordsLinked to original sources
USGS2022

Sediment sources and sealed-pavement area drive polycyclic aromatic hydrocarbon and metal occurrence in urban streams

Metals and polycyclic aromatic hydrocarbons (PAHs) are common pollutants in urban streambed sediment, yet their occurrence is highly variable and difficult to predict. To investigate sources of PAHs and metals to streambed sediment, we sampled pavement dust, soil, and streambed sediment in 10 urban watersheds in three regions of the United States and applied a fallout-radionuclide-based sediment-source analysis to quantify the pavement dust contribution to stream sediment (%dust). We also mapped the area of sealcoated pavement in each watershed (%sealed) to investigate the role of coal-tar pavement sealant (CTS) as a PAH source. Median total and carbon-normalized total PAH concentrations were significantly higher in streambed sediment in the Northeast (54.3 mg/kg and 2.71 mg/gOC) and Southeast (5.37 mg/kg and 1.36 mg/gOC), where CTS is commonly used, than in the Northwest (2.11 mg/kg and 0.071 mg/gOC), where CTS is rarely used. Generalized additive models indicated that %sealed and in some cases %dust significantly affected total PAH concentrations in streambed sediments. The %dust was a significant variable for common urban metals: Cu, Pb, and Zn. These findings advance our quantitative understanding of the role of pavement dust as a source and a vector of contaminants to urban streams.

Georgia, New York, North Carolina, Oregon, Virgini↗
USGS2022

New-generation pesticides are prevalent in California's Central Coast streams

Pesticides are widely recognized as important biological stressors in streams, especially in heavily developed urban and agricultural areas like the Central California Coast region. We assessed occurrence and potential toxicity of pesticides in small streams in the region using two analytical methods: a broad-spectrum (223 compounds) method in use since 2012 and a newly developed method for 30 additional new-generation fungicides and insecticides. At least one pesticide compound was identified in 83 of the 85 streams sampled. About one-half (48%) of the 253 pesticides measured were detected at least once and 27 were detected in 10% or more of samples. Three of the top 4, and 6 of the top 10 most frequently detected compounds (chlorantraniliprole, dinotefuran, boscalid, thiamethoxam, clothianidin and the fluopicolide degradate 2,6-dichlorobenzamide) were analyzed by the new method. Pesticide mixtures were common, with two or more pesticide compounds detected in 81% of samples and 10 or more in 32% of samples. The pesticide count at a site was relatively consistent over the 6-week study. Four sites with mixed land-use in the lower basin (<5 km from the sampling site) tended to have the highest pesticide counts and the highest concentrations. Potential toxicity (assessed by comparison to benchmarks) to invertebrates was much more common than potential toxicity to fish or plants and was associated with a wide array of insecticides. The common occurrence of new-generation pesticides highlights the need to continuously update analytical methods to keep pace with changing pesticide use for a fuller assessment of pesticide occurrence and effects on the environment.

California↗
USGS2022

Ecological consequences of neonicotinoid mixtures in streams

Neonicotinoid mixtures are common in streams worldwide, but corresponding ecological responses are poorly understood. We combined experimental and observational studies to narrow this knowledge gap. The mesocosm experiment determined that concentrations of the neonicotinoids imidacloprid and clothianidin (range of exposures, 0 to 11.9 μg/liter) above the hazard concentration for 5% of species (0.017 and 0.010 μg/liter, respectively) caused a loss in taxa abundance and richness, disrupted adult emergence, and altered trophodynamics, while mixtures of the two neonicotinoids caused dose-dependent synergistic effects. In 85 Coastal California streams, neonicotinoids were commonly detected [59% of samples ( n = 340), 72% of streams], frequently occurred as mixtures (56% of streams), and potential toxicity was dominated by imidacloprid (maximum = 1.92 μg/liter) and clothianidin (maximum = 2.51 μg/liter). Ecological responses in the field were consistent with the synergistic effects observed in the mesocosm experiment, indicating that neonicotinoid mixtures pose greater than expected risks to stream health.

Science Advances↗
USGS2021

Inclusion of pesticide transformation products is key to estimating pesticide exposures and effects in small U.S. streams

Improved analytical methods can quantify hundreds of pesticide transformation products (TPs), but understanding of TP occurrence and potential toxicity in aquatic ecosystems remains limited. We quantified 108 parent pesticides and 116 TPs in more than 3 700 samples from 442 small streams in mostly urban basins across five major regions of the United States. TPs were detected nearly as frequently as parents (90 and 95% of streams, respectively); 102 TPs were detected at least once and 28 were detected in >20% samples in at least one region—TPs of 9 herbicides, 2 fungicides (chlorothalonil and thiophanate-methyl), and 1 insecticide (fipronil) were the most frequently detected. TPs occurred commonly during baseflow conditions, indicating chronic environmental TP exposures to aquatic organisms and the likely importance of groundwater as a TP source. Hazard quotients based on acute aquatic-life benchmarks for invertebrates and nonvascular plants and vertebrate-centric molecular endpoints (sublethal effects) quantify the range of the potential contribution of TPs to environmental risk and highlight several TP exposure–response data gaps. A precautionary approach using equimolar substitution of parent benchmarks or endpoints for missing TP benchmarks indicates that potential aquatic effects of pesticide TPs could be underestimated by an order of magnitude or more.

Environmental Science and Technology↗
USGS2021

Multi-region assessment of chemical mixture exposures and predicted cumulative effects in USA wadeable urban/agriculture-gradient streams

Chemical-contaminant mixtures are widely reported in large stream reaches in urban/agriculture-developed watersheds, but mixture compositions and aggregate biological effects are less well understood in corresponding smaller headwaters , which comprise most of stream length, riparian connectivity, and spatial biodiversity. During 2014–2017, the U.S. Geological Survey (USGS) measured 389 unique organic analytes (pharmaceutical, pesticide, organic wastewater indicators) in 305 headwater streams within four contiguous United States (US) regions. Potential aquatic biological effects were evaluated for estimated maximum and median exposure conditions using multiple lines of evidence, including occurrence/concentrations of designed-bioactive pesticides and pharmaceuticals and cumulative risk screening based on vertebrate-centric ToxCast™ exposure-response data and on invertebrate and nonvascular plant aquatic life benchmarks. Mixed-contaminant exposures were ubiquitous and varied, with 78% (304) of analytes detected at least once and cumulative maximum concentrations up to more than 156,000 ng/L. Designed bioactives represented 83% of detected analytes. Contaminant summary metrics correlated strong-positive (rho (ρ): 0.569–0.719) to multiple watershed-development metrics, only weak-positive to point-source discharges (ρ: 0.225–353), and moderate- to strong-negative with multiple instream invertebrate metrics (ρ: −0.373 to −0.652). Risk screening indicated common exposures with high probability of vertebrate-centric molecular effects and of acute toxicity to invertebrates, respectively. The results confirm exposures to broad and diverse contaminant mixtures and provide convincing multiple lines of evidence that chemical contaminants contribute substantially to adverse multi-stressor effects in headwater-stream communities.

Science of the Total Environment↗
USGS2021

Is there an urban pesticide signature? Urban streams in five U.S. regions share common dissolved-phase pesticides but differ in predicted aquatic toxicity

Pesticides occur in urban streams globally, but the relation of occurrence to urbanization can be obscured by regional differences. In studies of five regions of the United States, we investigated the effect of region and urbanization on the occurrence and potential toxicity of dissolved pesticide mixtures. We analyzed 225 pesticide compounds in weekly discrete water samples collected during 6–12 weeks from 271 wadable streams; development in these basins ranged from undeveloped to highly urbanized. Sixteen pesticides were consistently detected in 16 urban centers across the five regions—we propose that these pesticides comprise a suite of urban signature pesticides (USP) that are all common in small U.S. urban streams. These USPs accounted for the majority of summed maximum pesticide concentrations at urban sites within each urban center. USP concentrations, mixture complexity, and potential toxicity increased with the degree of urbanization in the basin. Basin urbanization explained the most variability in multivariate distance-based models of pesticide profiles, with region always secondary in importance. The USPs accounted for 83% of pesticides in the 20 most frequently occurring 2-compound unique mixtures at urban sites, with carbendazim+prometon the most common. Although USPs were consistently detected in all regions, detection frequencies and concentrations varied by region, conferring differences in potential aquatic toxicity. Potential toxicity was highest for invertebrates (benchmarks exceeded in 51% of urban streams), due most often to the neonicotinoid insecticide imidacloprid and secondarily to organophosphate insecticides and fipronil. Benchmarks were rarely exceeded in urban streams for plants (at 3% of sites) or fish (<1%). We propose that the USPs identified here would make logical core (nonexclusive) constituents for monitoring dissolved pesticides in U.S. urban streams, and that unique mixtures containing imidacloprid, fipronil, and carbendazim are priority candidates for mixtures toxicity testing.

Science of the Total Environment↗
USGS2021

Multiple in-stream stressors degrade biological assemblages in five U.S. regions

Biological assemblages in streams are affected by a wide variety of physical and chemical stressors associated with land-use development, yet the importance of combinations of different types of stressors is not well known. From 2013 to 2017, the U.S. Geological Survey completed multi-stressor/multi-assemblage stream ecological assessments in five regions of the United States (434 streams total). Diatom, invertebrate, and fish communities were enumerated, and five types of potential stressors were quantified: habitat disturbance, excess nutrients, high flows, basic water quality, and contaminants in water and sediment. Boosted regression tree (BRT) models for each biological assemblage and region generally included variables from all five stressor types and multiple stressors types in each model was the norm. Classification and regression tree (CART) models then were used to determine thresholds for each BRT model variable above which there appeared to be adverse effects (multi-metric index (MMI) models only). In every region and assemblage there was a significant inverse relation between the MMI and the number of stressors exerting potentially adverse effects. The number of elevated instream stressors often varied substantially for a given level of land-use development and the number of elevated stressors was a better predictor of biological condition than was development. Using the adverse effects-levels that were developed based on the BRT model results, 68% of the streams had two or more stressors with potentially adverse effects and 35% had four or more. Our results indicate that relatively small increases in the number of stressors of different types can have a large effect on a stream ecosystem.

Science of the Total Environment↗
USGS2020

Biofilms provide new insight into pesticide occurrence in streams and links to aquatic ecological communities

Streambed sediment is commonly analyzed to assess occurrence of hydrophobic pesticides and risks to aquatic communities. However, stream biofilms also have the potential to accumulate pesticides and may be consumed by aquatic organisms. To better characterize risks to aquatic life, the U.S. Geological Survey Regional Stream Quality Assessment measured 93 current-use and 3 legacy pesticides in bed sediment and biofilm from 54 small streams in California across a range of land-use settings. On average, 4 times as many current-use pesticides were detected in biofilm at a site (median of 2) as in sediment (median of 0.5). Of 31 current-use pesticides detected, 20 were detected more frequently in biofilm than sediment and 10 equally frequently. Pyrethroids as a class were the most potentially toxic to benthic invertebrates, and of the nine pyrethroids detected, seven occurred more frequently in biofilm than sediment. We constructive General Additive Models to investigate relations between pesticides and six metrics of benthic community structure. Pesticides in biofilm improved fit in four of the six models, and pesticides in sediment improved fit in two. The results indicate that sampling of stream biofilms can complement bed-sediment sampling by identifying more current-use pesticides present and better estimating ecological risks.

California↗
USGS2020

Legacy and current‐use contaminants in sediments alter macroinvertebrate communities in southeastern US Streams

Sediment contamination of freshwater streams in urban areas is a recognized and growing concern. As a part of a comprehensive regional stream‐quality assessment, stream‐bed sediment was sampled from streams spanning a gradient of urban intensity in the Piedmont ecoregion of the southeastern United States. We evaluated relations between a broad suite of sediment contaminants (metals, current‐use pesticides, organochlorine pesticides, polychlorinated biphenyls, brominated diphenyl ethers, and polycyclic aromatic hydrocarbons), ambient sediment toxicity, and macroinvertebrate communities from 76 sites. Sediment toxicity was evaluated by conducting whole‐sediment laboratory toxicity testing with the amphipod Hyalella azteca (for 28 d) and the midge Chironomus dilutus (for 10 d). Approximately one‐third of the sediment samples were identified as toxic for at least one test species endpoint, although concentrations of contaminants infrequently exceeded toxicity benchmarks. Ratios of contaminant concentrations relative to their benchmarks, both individually and as summed benchmark quotients, were explored on a carbon‐normalized and a dry‐weight basis. Invertebrate taxa measures from ecological surveys tended to decline with increasing urbanization and with sediment contamination. Toxicity test endpoints were more strongly related to sediment contamination than invertebrate community measures were. Sediment chemistry and sediment toxicity provided moderate and weak, respectively, explanatory power for the similarity/dissimilarity of invertebrate communities. The results indicate that current single‐chemical sediment benchmarks may underestimate the effects from mixtures of sediment contaminants experienced by lotic invertebrates.

Alabama, Georgia, South Carolina, North Carolina, ↗
USGS2020

Pavement alters delivery of sediment and fallout radionuclides to urbanstreams

Sediment from urban impervious surfaces has the potential to be an important vector for contaminants, particularly where stormwater culverts and other buried channels draining large impervious areas exit from underground pipes into open channels. To better understand urban sediment sources and their relation to fallout radionuclides, we collected samples of rainfall, urban sediment (pavement sediment, topsoil), streambank sediment, and fluvial sediment (suspended sediment and bed sediment) for 7 Be, 210 Pb ex , and 137 Cs analysis. The results indicate that each rainfall event tags pavement sediment with elevated activities of 7 Be and 210 Pb ex such that runoff from impervious surfaces in the buried channel part of the stream network contains the highest activities. Pavement sediment, because it is characteristically a thin veneer, has a small mass to rainwater ratio resulting in a greater tagging of 7 Be and 210 Pb ex activity than does topsoil on a per gram basis. An unmixing model indicated that suspended-sediment samples collected at the culvert outlet from the buried-channel network are from pavement sediment sources (45 ± 25%) with a smaller component of topsoil (22 ± 19%), and a component from streambanks (32 ± 35%) that we infer to be older channel material and subsoil eroded from within the culvert system. Downstream from the culvert, suspended sediment collected from the open-channel parts of the stream had 7 Be and 210 Pb ex activities that were substantially reduced by the contribution of sediment from streambanks (57 ± 15%), with pavement contributions decreasing to 15 (±9%) and topsoil contributing 28 (±7%). The results highlight the utility of 7 Be, 210 Pb ex , and 137 Cs as tracers of urban sediment sources, resulting in a unique radionuclide signature for urban watersheds compared to other sediment-source settings.

Maryland↗
USGS2020

Daily stream samples reveal highly complex pesticide occurrence and potential toxicity to aquatic life

Transient, acutely toxic concentrations of pesticides in streams can go undetected by fixed-interval sampling programs. Here we compare temporal patterns in occurrence of current-use pesticides in daily composite samples to those in weekly composite and weekly discrete samples of surface water from 14 small stream sites. Samples were collected over 10–14 weeks at 7 stream sites in each of the Midwestern and Southeastern United States. Samples were analyzed for over 200 pesticides and degradates by direct aqueous injection liquid chromatography with tandem mass spectrometry. Nearly 2 and 3 times as many unique pesticides were detected in daily samples as in weekly composite and weekly discrete samples, respectively. Based on exceedances of acute-invertebrate benchmarks (AIB) and(or) a Pesticide Toxicity Index (PTI) >1, potential acute-invertebrate toxicity was predicted at 11 of 14 sites from the results for daily composite samples, but was predicted for only 3 sites from weekly composites and for no sites from weekly discrete samples. Insecticides were responsible for most of the potential invertebrate toxicity, occurred transiently, and frequently were missed by the weekly discrete and composite samples. The number of days with benthic-invertebrate PTI ≥0.1 in daily composite samples was inversely related to Ephemeroptera, Plecoptera, and Trichoptera (EPT) richness at the sites. The results of the study indicate that short-term, potentially toxic peaks in pesticides frequently are missed by weekly discrete sampling, and that such peaks may contribute to degradation of invertebrate community condition in small streams. Weekly composite samples underestimated maximum concentrations and potential acute-invertebrate toxicity, but to a lesser degree than weekly discrete samples, and provided a reasonable approximation of the 90th percentile total concentrations of herbicides, insecticides, and fungicides, suggesting that weekly composite sampling may be a compromise between assessment needs and cost.

Science of the Total Environment↗
USGS2020

Common insecticide disrupts aquatic communities: A mesocosm-to-field ecological risk assessment of fipronil and its degradates in U.S. streams

Insecticides in streams are increasingly a global concern, yet information on safe concentrations for aquatic ecosystems is sparse. In a 30-day mesocosm experiment exposing native benthic aquatic invertebrates to the common insecticide fipronil and four degradates, fipronil compounds caused altered emergence and trophic cascades. Effect concentrations eliciting a 50% response (EC 50 ) were developed for fipronil and its sulfide, sulfone, and desulfinyl degradates; taxa were insensitive to fipronil amide. Hazard concentrations for 5% of affected species derived from up to 15 mesocosm EC 50 values were used to convert fipronil compound concentrations in field samples to the sum of toxic units (∑TU Fipronils ). Mean ∑TU Fipronils exceeded 1 (indicating toxicity) in 16% of streams sampled from five regional studies. The Species at Risk invertebrate metric was negatively associated with ∑TU Fipronils in four of five regions sampled. This ecological risk assessment indicates that low concentrations of fipronil compounds degrade stream communities in multiple regions of the United States.

Science Advances↗
USGS2019

Flow modification in the Nation’s streams and rivers

This report summarizes a national assessment of flowing waters conducted by the U.S. Geological Survey’s (USGS) National Water-Quality Assessment (NAWQA) Project and addresses several pressing questions about the modification of natural flows in streams and rivers. The assessment is based on the integration, modeling, and synthesis of monitoring data collected by the USGS and the U.S. Environmental Protection Agency at more than 7,000 streams and rivers across the conterminous United States from 1980 to 2014. Key findings include the following. First, flow in many of the Nation’s streams and rivers is different from what it would be under natural conditions. In particular, low flows are more frequent, are of shorter duration, and vary less from one year to the next than they would naturally. In addition, high flows have been reduced in magnitude, are of shorter duration, are less frequent, and vary less from one year to the next than they would naturally. Other characteristics of natural flows also have been modified. Second, over the last 60 years (1955–2014), climatic trends have caused a change of 50 percent or more in one or more streamflow attributes at two-thirds of climate-sensitive streamgaging sites. However, these climate-induced changes have been less influential on streamflow modification than have land and water-management practices. Third, in every region assessed, streamflow modification was associated with reduced ecological health, as indicated by two biological communities—invertebrates and fish. Biological communities were increasingly likely to be impaired (defined as having lost a statistically significant number of species) in streams with flows most different from natural conditions. Finally, several case studies are presented that illustrate viable management strategies for balancing the water needs of people and ecosystems.

Circular↗
USGS2019

Projected urban growth in the Southeastern USA puts small streams at risk

Future land-use development has the potential to profoundly affect the health of aquatic ecosystems in the coming decades. We developed regression models predicting the loss of sensitive fish (R2=0.39) and macroinvertebrate (R2=0.64) taxa as a function of urban and agricultural land uses and applied them to projected urbanization of the rapidly urbanizing Piedmont ecoregion of the southeastern USA for 2030 and 2060. The regression models are based on a 2014 investigation of water quality and ecology of 75 wadeable streams across the region. Based on these projections, stream kilometers experiencing >50% loss of sensitive fish and invertebrate taxa will nearly quadruple to 19,500 and 38,950 km by 2060 (16 and 32% of small stream kilometers in the region), respectively. Uncertainty was assessed using the 20 and 80% probability of urbanization for the land-use projection model and using the 95% confidence intervals for the regression models. Adverse effects on stream health were linked to elevated concentrations of contaminants and nutrients, low dissolved oxygen, and streamflow alteration, all associated with urbanization. The results of this analysis provide a warning of potential risks from future urbanization and perhaps some guidance on how those risks might be mitigated.

PLoS ONE↗
USGS2019

Emerging contaminants in groundwater, karst, and the Edwards Aquifer

Karst aquifers have hydrogeologic characteristics that render them uniquely vulnerable to contamination from emerging contaminants (ECs). ECs comprise numerous chemical groups, including pharmaceuticals, personal-care products, flame retardants, perfluorinated and polyfluorinated compounds, nanoparticles and microplastics. Many ECs have sources, transport pathways, and chemical characteristics that facilitate their infiltration into groundwater, either indirectly from surface water or directly from sources such as landfill leachate and septic systems. What little is known about the occurrence, fate, and transport of ECs in the Edwards aquifer indicates that the aquifer might be increasingly vulnerable to this type of contamination. The natural physical characteristics of this karst aquifer and anthropogenic sources of ECs associated with increased urbanization in central Texas contribute to this vulnerability. In this chapter, we review groups of ECs and their sources, occurrence of ECs in groundwater and karst, and what is known about occurrence of ECs in the Edwards aquifer. We conclude by discussing specific factors, such as rapid flow and contaminant sources, that contribute to the vulnerability of the Edwards aquifer to contamination by ECs.

Texas↗
USGS2018

Water-quality observations of the San Antonio segment of the Edwards aquifer, Texas, with an emphasis on processes influencing nutrient and pesticide geochemistry and factors affecting aquifer vulnerability, 2010–16

As questions regarding the influence of increasing urbanization on water quality in the Edwards aquifer are raised, a better understanding of the sources, fate, and transport of compounds of concern in the aquifer—in particular, nutrients and pesticides—is needed to improve water management decision-making capabilities. The U.S. Geological Survey, in cooperation with the San Antonio Water System, performed a study from 2010 to 2016 to better understand how water quality changes under a range of hydrologic conditions and in contrasting land-cover settings (rural and urban) in the Edwards aquifer. The study design included continuous hydrologic monitoring, continuous water-quality monitoring, and discrete sample collection for a detailed characterization of water quality at a network of sites throughout the aquifer system. The sites were selected to encompass a “source-to-sink” (that is, from aquifer recharge to aquifer discharge) approach. Network sites were selected to characterize rainfall, recharging surface water, and groundwater; groundwater sites included wells in the unconfined part of the aquifer (unconfined wells) and in the confined part of the aquifer (confined wells) and a major discharging spring. Storm-related samples—including rainfall samples, stormwater-runoff (surface-water) samples, and groundwater samples—were collected to characterize the aquifer response to recharge. Elevated nitrate concentrations relative to national background values and the widespread detection of pesticides indicate that the Edwards aquifer is vulnerable to contamination and that vulnerability is affected by factors such as land cover, aquifer hydrogeology, and changes in hydrologic conditions. Greater vulnerability of groundwater in urban areas relative to rural areas was evident from results for urban groundwater sites, which generally had higher nitrate concentrations, elevated δ 15 N-nitrate values, a greater diversity of pesticides, and higher pesticide concentrations. The continuum of water quality from unconfined rural groundwater sites (least affected by anthropogenic contamination) to unconfined urban groundwater sites (most affected by anthropogenic contamination) demonstrates enhanced vulnerability of urban versus rural land cover. Differences in contaminant occurrences and concentration among unconfined urban wells indicate that the urban parts of the aquifer are not uniformly vulnerable, but rather are affected by spatial differences in the sources of nutrients and pesticides. In urban areas, the shallow, unconfined groundwater sites showed greater temporal variability in both nutrient and pesticide concentrations, as well as a greater degree of contamination, than did deeper, confined groundwater sites. In comparison to that of the shallow, unconfined groundwater sites, the water quality of the deeper, confined groundwater sites was relatively invariant during this multiyear study. Although aquifer hydrogeology is an important factor related to aquifer vulnerability, land cover likely has a greater influence on pesticide contamination of groundwater. Temporal variability in hydrologic conditions for the Edwards aquifer is apparent in data for surface water as a source of groundwater recharge, water-level altitude in wells, spring discharge, and groundwater quality. This temporal variability affects recharge sources, recharge amounts, groundwater traveltimes, flow routing, water-rock interaction processes, dilution, mixing, and, in turn, water quality. Relations of land cover, aquifer hydrogeology, and changing hydrologic conditions to water quality are complex but provide insight into the vulnerability of Edwards aquifer groundwater—a vital drinking-water resource.

Texas↗
USGS2018

The Midwest Stream Quality Assessment—Influences of human activities on streams

Healthy streams and the fish and other organisms that live in them contribute to our quality of life. Extensive modification of the landscape in the Midwestern United States, however, has profoundly affected the condition of streams. Row crops and pavement have replaced grasslands and woodlands, streams have been straightened, and wetlands and fields have been drained. Runoff from agricultural and urban land brings sediment and chemicals to streams. What is the chemical, physical, and biological condition of Midwestern streams? Which physical and chemical stressors are adversely affecting biological communities, what are their origins, and how might we lessen or avoid their adverse effects? In 2013, the U.S. Geological Survey (USGS) conducted the Midwest Stream Quality Assessment to evaluate how human activities affect the biological condition of Midwestern streams. In collaboration with the U.S. Environmental Protection Agency National Rivers and Streams Assessment, the USGS sampled 100 streams, chosen to be representative of the different types of watersheds in the region. Biological condition was evaluated based on the number and diversity of fish, algae, and invertebrates in the streams. Changes to the physical habitat and chemical characteristics of the streams—“stressors”—were assessed, and their relation to landscape factors and biological condition was explored by using mathematical models. The data and models help us to better understand how the human activities on the landscape are affecting streams in the region.

Fact Sheet↗