Barbara Mahler
Barbara Mahler is a Research Hydrologist and Communications Coordinator for the USGS Water Mission Area. Her research interests include fate and transport of contaminated sediment, and karst hydrology and water quality.
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 has been an Associate Editor for the Journal of Hydrology, and is 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 Science, Nature, 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 at approximately 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.
USGS Research: PAHs and Coal-Tar-Based Pavement Sealcoat
Coal-tar-based pavement sealant is a potent source of polycyclic aromatic hydrocarbons (PAHs), as documented by the USGS and other researchers.
Coal-tar-based sealcoat products typically are 20 to 35% coal tar or coal-tar pitch—these materials are...
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...
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...
Nowell, Lisa H.; Moran, Patrick W.; Bexfield, Laura M.; Mahler, Barbara; Van Metre, Peter C.; Bradley, Paul; Schmidt, Travis S.; Button, Daniel T.; Qi, Sharon L. 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...
Mahler, Barbara; Nowell, Lisa H.; Sandstrom, Mark W.; Bradley, Paul; Romanok, Kristin; Konrad, Christopher; Van Metre, Peter 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,...
Bradley, Paul; Journey, Celeste A.; Romanok, Kristin; Breitmeyer, Sara; Button, Daniel T.; Carlisle, Daren M.; Huffman, Bradley; Mahler, Barbara; Nowell, Lisa H.; Qi, Sharon L.; Smalling, Kelly; Waite, Ian R.; Van Metre, Peter C. Editorial: Advances in hydrology and the water environment in the karst critical zone under the impacts of climate change and anthropogenic activities
No abstract available.
Mahler, Barbara; Yongjun, Jiang; Pu, Junbing; Martin, Jonathan 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...
Waite, Ian R.; Van Metre, Peter C.; Moran, Patrick W.; Konrad, Christopher P.; Nowell, Lisa H.; Meador, Michael R.; Munn, Mark D.; Schmidt, Travis S.; Gellis, Allen; Carlisle, Daren; Bradley, Paul M.; Mahler, Barbara 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 M.; Munn, Mark D.; May, Jason 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...
Gellis, Allen; Fuller, Christopher C.; Van Metre, Peter C.; Mahler, Barbara; Welty, C.; Miller, Andrew; Nibert, Lucas A; Clifton, Zachary; Malen, Jeremy; Kemper, J.T. 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...
Moran, Patrick W.; Kemble, Nile E.; Waite, Ian R.; Mahler, Barbara; Nowell, Lisa H.; Van Metre, Peter C.
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; 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 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
Pesticide transformation products are nearly ubiquitous in small U.S. streams
Pesticide transformation products (TPs) may be a critical missing piece of the toxicity puzzle for aquatic life in small U.S. streams, according to a new study by the USGS.
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.