WILLISTON, N.D. — A United States Geological Survey study published in May examined how historic oil and gas production in a portion of the Williston Basin has affected native amphibians there.
The Prairie Pothole Region of eastern Montana, western North Dakota, South Dakota and southern Saskatchewan is pocked with small, shallow wetlands that offer important ecosystems for aquatic species and migratory birds.
The USGS scientists, led by research hydrologist Kelly Smalling, went beyond merely measuring the levels of various metals in the water — they also evaluated buildup in sediment and in several amphibian species, including the barred tiger salamander, the northern leopard frog and the boreal chorus frog.
According to the study, saline wastewater, or brine, created during energy production often contain elevated concentrations of toxic metals, hydrocarbons, volatile organic compounds, ammonium and radionuclides, which can alter water quality and accumulate in sediment, resulting in negative consequences for wildlife.
“We focused on larval amphibians in this study, and some frog species like leopard frogs and chorus frogs spend a lot of time at the bottom of the wetlands feeding,” Smalling said in an email. “During feeding they have the potential to take up metals directly from the sediment, so it's another important route of exposure. Water-only exposure to metals ignore the feeding component and just look at exposure across the gills and through the skin.”
Smalling said amphibians were chosen as the focus because current research suggests amphibians are especially sensitive to changes in the salinization of wetlands due to their permeable skin.
“Amphibian species are declining worldwide and habitat loss and fragmentation are some big drivers, so preserving quality habitat is important in maintaining populations,” she said.
Ultimately, the study sampled wetlands across a range of brine contamination histories and a range of low to moderate contamination levels, and did not find a strong association between contamination in larval amphibian tissue or in sediment with brine contamination.
Smalling pointed out that although the study was not able to correlate the metals detected with oil and gas production, those substances are still present at Williston Basin.
“Based on our results from this and other studies, there are multiple interacting stressors from varying sources that could result in effects on the amphibians,” Smalling said. “Understanding these multiple stressors is complicated, but one of the keys in preserving habitat and maintaining healthy populations.”