Barbara Mahler
Barbara Mahler is a Research Hydrologist and Communications Coordinator for the USGS National Water Quality Program. Her research interests include fate and transport of contaminated sediment, and karst hydrology and water quality.
Mahler 2017 CV
Biography
Barbara has Masters and doctoral degrees in Geology from the University of Texas, where she studied with Dr. Philip Bennett. The emphasis of her graduate research was the geochemistry of karst aquifers. Her doctoral research focused on sediment transport through karst aquifers and its potential to serve as a vector for contaminant transport. After completing her Ph.D. in 1997, she spent 1 year as an NSF/NATO International Postdoc in Montpellier, France, studying transport of sediment and bacteria in karst.
Currently Barbara is a geochemist with the NWQP Regional Stream Quality Assessment (RSQA) study, and the Communications Coordinator for the USGS National Water Quality Program (NWQP). Her research has highlighted the role played by coal-tar-based pavement sealants in contributing polycyclic aromatic hydrocarbons (PAHs) to the environment, for which was was awarded the USGS Meritorious Service Award in 2017. Her publications in the field of karst have included analysis of pesticide breakthrough curves in spring flow, use of nitrate as a tracer of recent recharge, and use of principal components analysis to investigate nutrient dynamics in karst. She is an Associate Editor for the Journal of Hydrology, and a member of the IAH Karst Hydrogeology Commission.
Barbara is a Research Fellow at the University of Texas Jackson School of Geosciences. She regularly serves on the committees of Masters and Ph.D. students and teaches courses at the university. She is a regular reviewer for numerous scientific journals, including Journal of Hydrology, Hydrogeology Journal, Environmental Science and Technology, and Journal of Contaminant Hydrology.
Science and Products
USGS Streamgaging Network
The USGS Groundwater and Streamflow Information Program supports the collection and (or) delivery of both streamflow and water-level information for more than 8,500 sites and water-level information alone for more than 1,700 additional sites. The data are served online—most in near realtime—to meet many diverse needs.
Urban Land Use and Water Quality
Wherever you live, there’s a creek or stream near you. The eighty percent of Americans who live in metropolitan areas are often unaware of the network of urban creeks—many teeming with life—that weaves through our cities and town. Nowhere are the environmental changes associated with urban development more evident than in urban streams.
NWQP Water-Quality Topics
From chloride to corrosivity, from pesticides to PAHs, find the most recent National Water Quality Program (NWQP) science on these topics and effects on surface water, groundwater, and ecology. Informative web pages provide an overview and links to related web pages, publications, maps, news, and data.
Coal-Tar-Based Pavement Sealcoat, PAHs, and Environmental Health
Sealcoat is the black, viscous liquid applied to many asphalt parking lots, driveways, and playgrounds in North America to protect and enhance the appearance of the underlying asphalt. Coal-tar-based pavement sealcoat is a potent source of polycyclic aromatic hydrocarbon (PAH) contamination in urban and suburban areas and a potential concern for human health and aquatic life.
Water-Quality Quick Links
Looking for data? Maps? Use the links below to quickly access some of the most frequently visited USGS web pages on water quality.
National Water-Quality Project Sampling Methods
USGS National Water Quality Assessment (NAWQA) studies require analyses of stream and bed-sediment samples for major ions, nutrients, sediments, and organic contaminants that are consistent across time and space. Procedures have been designed specifically to produce...
Water-Quality Trends
Is water quality getting better or worse? Answering this deceptively simple question has been a fundamental objective of the USGS National Water-Quality Assessment Project’s research. Learn about trends in contaminants in the nation’s streams and rivers, trends in contaminants that collect in the bed sediment of streams and lakes, and changes in the quality of the nation’s groundwater.
Sediment-Associated Contaminants
Stream, river, and lake bed sediment are reservoirs for many contaminants. These contaminants include some “legacy” contaminants, like DDT, PCBs, and chlordane, and chemicals currently in use, like the insecticide bifenthrin and many flame retardants. Learn about techniques used to study sediment-associated contaminants and their importance to aquatic biota.
Webinar: Karst, Critters, and Climate Change: A Multidisciplinary Evaluation of Karst Species Vulnerability to Climate Change
View this webinar to learn how scientists are exploring the vulnerability of karst species to climate change.
Evaluating the Impacts of Climate Extremes on Karst Hydrology and Species Vulnerability
Karst aquifers—formed when the movement of water dissolves bedrock—are critical groundwater resources in North America. Water moving through these aquifers carves out magnificent caves, sinkholes, and other formations. These formations are home to high concentrations of rare and endangered species, but the hydrological conditions that support these species can change rapidly. Managing these...
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...
Mahler, Barbara; Schmidt, Travis S.; Nowell, Lisa H.; Qi, Sharon L.; Van Metre, Peter C.; Hladik, Michelle; Carlisle, Daren; Munn, Mark D.; May, Jason 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...
Norman, Julia E.; Mahler, Barbara; Nowell, Lisa H.; Van Metre, Peter C.; Sandstrom, Mark W.; Corbin, Mark A.; Qian, Yaorong; Pankow, James F.; Luo, Wentai; Fitzgerald, Nicholas B.; Asher, William E.; McWhirter, Kevin J.
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...
Carlisle, Daren M.; Wolock, David M.; Konrad, Christopher P.; McCabe, Gregory J.; Eng, Ken; Theodore E. Grantham; Mahler, Barbara 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...
Van Metre, Peter C.; Waite, Ian R.; Qi, Sharon L.; Mahler, Barbara; Terando, Adam; Wieczorek, Michael; Meador, Michael R.; Bradley, Paul M.; Journey, Celeste A.; Schmidt, Travis S.; Carlisle, Daren M. 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,...
Mahler, Barbara; Musgrove, Marylynn
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...
Opsahl, Stephen P.; Musgrove, MaryLynn; Mahler, Barbara; Lambert, Rebecca B.
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...
Van Metre, Peter C.; Mahler, Barbara; Carlisle, Daren M.; Coles, James F. Complex mixtures of dissolved pesticides show potential aquatic toxicity in a synoptic study of Midwestern U.S. streams
Aquatic organisms in streams are exposed to pesticide mixtures that vary in composition over time in response to changes in flow conditions, pesticide inputs to the stream, and pesticide fate and degradation within the stream. To characterize mixtures of dissolved-phase pesticides and degradates in Midwestern streams, a synoptic study was...
Nowell, Lisa H.; Moran, Patrick W.; Schmidt, Travis S.; Norman, Julia E.; Nakagaki, Naomi; Shoda, Megan E.; Mahler, Barbara; Van Metre, Peter C.; Stone, Wesley W.; Sandstrom, Mark W.; Hladik, Michelle L. Influence of sediment chemistry and sediment toxicity on macroinvertebrate communities across 99 wadable streams of the Midwestern USA
Simultaneous assessment of sediment chemistry, sediment toxicity, and macroinvertebrate communities can provide multiple lines of evidence when investigating relations between sediment contaminants and ecological degradation. These three measures were evaluated at 99 wadable stream sites across 11 states in the Midwestern United States during the...
Moran, Patrick W.; Nowell, Lisa H.; Kemble, Nile E.; Mahler, Barbara; Waite, Ian R.; Van Metre, Peter C. Complex mixtures of Pesticides in Midwest U.S. streams indicated by POCIS time-integrating samplers
The Midwest United States is an intensely agricultural region where pesticides in streams pose risks to aquatic biota, but temporal variability in pesticide concentrations makes characterization of their exposure to organisms challenging. To compensate for the effects of temporal variability, we deployed polar organic chemical integrative samplers...
Van Metre, Peter C.; Alvarez, David; Mahler, Barbara; Nowell, Lisa H.; Sandstrom, Mark W.; Moran, Patrick W. Coal-tar-based pavement sealants—a potent source of PAHs
P avement sealants are applied to the asphalt pavement of many parking lots, driveways, and even playgrounds in North America (Figure 1), where, when first applied, they render the pavement glossy black and looking like new. Sealant products used commercially in the central, eastern, and northern United States typically are coal-tarbased, whereas...
Mahler, Barbara; Van Metre, Peter C. Similarities and differences in occurrence and temporal fluctuations in glyphosate and atrazine in small Midwestern streams (USA) during the 2013 growing season
Glyphosate and atrazine are the most intensively used herbicides in the United States. Although there is abundant spatial and temporal information on atrazine occurrence at regional scales, there are far fewer data for glyphosate, and studies that compare the two herbicides are rare. We investigated temporal patterns in glyphosate and atrazine...
Mahler, Barbara; Van Metre, Peter C.; Burley, Thomas E.; Loftin, Keith A.; Meyer, Michael T.; Nowell, Lisa H.
A slimy source of information on pesticides in streams
Analysis of stream biofilms reveals the presence of a wider array of pesticides than analysis of bed sediment, reports a new study by the U.S. Geological Survey Regional Stream Quality Assessment. Biofilm analysis may also be a better predictor of potential adverse effects on the community...
Daily sampling of pesticides in streams
When scientists collected samples every day from 14 streams and analyzed them for pesticides, they found more pesticides and higher concentrations than when only weekly samples were analyzed. A new study reports that samples collected daily detected twice as many different pesticides over the 10–12-...
What's In Your Stream? Get Online to Find Out!
A new update to an online interactive tool for learning about pesticides, nutrients, and overall stream health in major regions of the U.S. is available from the U.S. Geological Survey’s Regional Stream Quality Assessment.
Midwest US: What’s in Your Stream? Get Online to Find Out!
An online interactive tool for learning about pesticides, nutrients, and the overall health of Midwest streams is now available from the U.S. Geological Survey. This information can be used by the public and resource managers to better understand the relative effects of these stressors on aquatic organisms in streams.
Coal-Tar-Sealant Runoff Causes Toxicity and DNA Damage
Runoff from pavement with coal-tar-based sealant is toxic to aquatic life, damages DNA, and impairs DNA repair, according to two studies by the U.S. Geological Survey published in the journals Environmental Science and Technology and Science of the Total Environment.
The Quality of the Nation’s Groundwater
About 115 million people—more than one-third of the Nation’s population—rely on groundwater for drinking water. As the Nation’s population grows, the need for high-quality drinking-water supplies becomes even more urgent.