USGS and Partners Release Results on Cycles of Mercury and Contaminants in Great Salt Lake, Utah

Scientists are discovering new pathways for toxic mercury to “bioaccumulate” in shrimp and waterfowl dependent upon the Great Salt Lake, Utah. A deep brine layer known to contain elevated levels of toxic methyl mercury has the potential to mix into the biologically active upper layers of the lake during sustained wind events in summer and fall. Brine shrimp and grebes were tested and found to have up to three times the average amount of mercury at these times of year.

Scientific instruments deployed in Great Salt Lake showed that temporary mixing of elevated methyl mercury concentrations in a deep brine layer could occur during sustained wind events. Once in the biologically active parts of the lake, the methyl mercury has the potential to bioaccumulate in the brine shrimp and birds that utilize the lake. Mercury was found to accumulate in brine shrimp, a food source for many of the birds that use Great Salt Lake. Eared Grebes use brine shrimp as their primary food source during the fall molting period when they replace their feathers. During this time (about 3-5 months) the grebes cannot fly and remain on Great Salt Lake. Average mercury concentrations measured in eared grebe livers increased by almost three times during the fall molting period.

The amount of mercury in the brine shrimp and birds varies seasonally as does the type of food that is available to those plants and animals that rely on the lake. Changes in the food supply can be monitored by changes in the chemical signatures of the food. Seasonal changes in the stable isotope ratios of nitrogen in brine shrimp also were observed during the study. “We found that the composition of isotopes found in brine shrimp change in a consistent manner over the growing season, likely reflecting a change in the type of algae that the brine shrimp were eating,” Dave Naftz, principal USGS author of the report said. “During the late spring and summer time periods the isotopic composition of the brine shrimp indicated that they were consuming a different type of algae, likely blue-green algae that obtain nitrogen directly from the atmosphere.”

Scientists at the U.S. Geological Survey (USGS), U.S. Fish and Wildlife Service (USFWS), Utah Division of Wildlife Resources (DWR), and Utah Division of Water Quality (DWQ) used water, brine shrimp, and waterbird samples to evaluate impacts from nutrient and mercury inputs to Great Salt Lake. Their report, entitled “Anthropogenic influences on the input and biogeochemical cycling of nutrients and mercury in Great Salt Lake, Utah, USA” was published this month in the international journal, Applied Geochemistry.

Copies of the report are available free of charge and can be obtained in person or by mail from the U.S. Geological Survey, 2329 West Orton Circle Salt Lake City, Utah, 84119. Electronic mail requests for the report should be sent to dlnaftz@usgs.gov. Funding for this research was provided by the UDWR, UDWQ, USFWS, and USGS.