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Barbara J Mahler

Research Hydrologist

Oklahoma-Texas Water Science Center

Office Phone: 512-927-3566
Fax: 512-927-3590
ORCID: 0000-0002-9150-9552

Texas Water Science Center - Austin
1505 Ferguson Lane
Austin , TX 78754-4501

Supervisor: Jennifer T Wilson
Temporal patterns in glyphosate and atrazine concentrations were measured weekly by the U.S. Geological Survey (USGS) during the 2013 growing season in 100 small streams in the Midwestern United States. Concentrations also were measured every 2 days at a subset of 8 of the sites, all located in Missouri. Glyphosate was detected more frequently in urban streams than in agricultural streams, and at concentrations similar to those in streams with high agricultural land use in the watershed. In contrast, atrazine was detected more frequently and at higher concentrations in agricultural streams than in urban streams. This data release provides watershed characteristics and 2013 glyphosate and atrazine compound concentrations...
These data present chemistry and toxicity results from freshwater stream sediments collected from 99 wadable stream sites across eleven states in the Midwestern U.S. as one component of a larger USGS study in the summer of 2013. This data presents a selected suite of chemistry collected at these sites (PAHs, Organochlorines, PCBs, Trace Elements, and current use pesticides) used in calculating a Probable Effect Concentration-Likely Effect Benchmark quotient mixture score for contaminants measured in sediments. The toxicity data presents results of toxicity tests following ASTM and US EPA standard methods for sediment toxicity tests with the amphipod Hyalella azteca (28-d exposure), the midge Chironomus dilutus (10-d),...
Webinar Summary: One-half of North American imperiled species live in subterranean habitats, which largely are associated with karst (a type of landscape underlain by limestone that has been eroded over time, producing caves, sinkholes, towers and other formations). Further, karst aquifers provide a unique opportunity to investigate the effects of climate change on groundwater at timescales of human interest because these aquifers exhibit large variability in hydrologic responses, such as springflow (i.e. groundwater discharge) and water-table level (i.e. level below which the ground is completely saturated with water), at short timescales. By linking a global climate, regional climate, and hydrologic model, researchers...
The Edwards aquifer is a karst aquifer system that is a primary water source for a large part of central Texas including the city of San Antonio, Texas. These vector geospatial data represent the geographic extent of the contributing zones for the Northern, Barton Springs, and San Antonio segments of the Edwards aquifer. The contributing zone is defined as the drainage area of the Edwards Plateau that contributes surface water to the Edwards aquifer recharge zone. The recharge zone is where surface water and precipitation infiltrate into the outcrop of the rocks that compose the aquifer (see Ashworth and Hopkins, 1995, and George and others, 2011). References Ashworth, J.B., and Hopkins, Janie, 1995, Aquifers of...
Dissolved pesticides were measured in weekly water samples from 482 wadeable streams in five regions of the United States during 2013-2017, as part of the U.S. Geological Survey's (USGS) Regional Stream Quality Assessment (RSQA). One study was conducted each year, starting with the Midwest (2013), followed by the Southeast Piedmont (2014), Pacific Northwest (2015), Northeast (2016), and Central California Coast (2017). Within each region, 77-100 streams were sampled over 6-14 weeks, followed by ecological surveys of fish, invertebrate and fish communities. The first study (Midwest) is an agricultural-gradient study, where the majority of sites were located along a gradient from undeveloped to 100% agricultural land...
Types: Map Service, OGC WFS Layer, OGC WMS Layer, OGC WMS Service; Tags: Alabama, California, Central California Foothills ecoregion, Coastal Mountains ecoregion, Connecticut, All tags...
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