Study Finds Flooding Can Increase Mercury Levels in Some Lakes

Jim Stone, Ph.D. is one of the researchers on this study. He stands next to a fish consumption advisory warning on a lake in South Dakota.

A study by researchers at the South Dakota School of Mines & Technology on the concentration of mercury in the sediments of seven South Dakota lakes found that the pollutant generally enters the water bodies through runoff and can increase during times of flooding and lake expansion. 

The paper, titled “Historical sediment mercury deposition for select South Dakota, USA, lakes: implications for watershed transport and flooding,” was published this year in the Journal of Soils and Sediments.

Emissions from coal fired power plants are the main source of mercury pollution around the world. Mercury is distributed through the atmosphere until it settles on the land. Global deposition of mercury began with the start of the industrial revolution and peaked in the United States in the 1970s. The concentrations have gone down with emission reductions and pollution control in more recent decades. Historic mining and industrial operations are less common sources of mercury pollution.

The objective of the study was to determine the main source of mercury and to understand the history of mercury deposition on a diverse range of lakes in the state. The study included Wall Lake, West 81 Lake, Lynn Lake, Island Lake, Lake Hurley and Lake Sinai in the eastern part of the state, and Lake Isabel in the western part of the state. The study was undertaken during the winter months when researchers drilled through the ice on the frozen lakes and took core samples of the mud on the lake bottom. By carbon dating the layers that were deposited in years past, they were able to look at the history of mercury deposition over the past century. 

Mercury accumulation from the atmosphere on the land is eventually washed into waterways, wetlands and lakes where it can build up in sediment and/or be chemically changed in form to enter the aquatic food chain and then accumulate in fish. The research concludes that, “Mercury in the sampled South Dakota lakes appears to emanate from watershed transport due to erosion from agricultural land use common to the Northern Great Plains.” The research also shows that “For sampled South Dakota lakes, watershed inputs are more significant sources of Hg (mercury) than atmospheric deposition.”  

Two sites, Lake Sinai and West 81 Lake near Brookings, have undergone cycles of flooding and drought in recent decades. “These lakes showed a tremendous increase in mercury following times of lake expansion and flooding,” says Dr. Jim Stone, one of the researchers on the study. The ultimate source of the pollution is the atmospheric deposition of mercury. “But once it falls to the ground the way the watershed is managed can impact how it ends up in these lakes,” says Stone.  

The study was undertaken by Maria K. Squillace, Heidi L. Sieverding and Jim Stone, Ph.D., in the Department of Civil and Environmental Engineering, and Hailemelekot H. Betemariam in the Department of Geology and Geological Engineering at SD Mines. Others at University of Wisconsin-Platteville, North Dakota State University and Michigan Technological University also contributed to the work.

The South Dakota Department of Heath maintains a list of lakes in the state with mercury advisories. 

 

Last edited 8/1/2019 10:37:15 AM

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