Connecting Water Levels to Water Quality: The Case of Mercury

By Michael Twiss, Clarkson University

Graduate student Evie Brahmtsedt of Clarkson University
Graduate student Evie Brahmtsedt of Clarkson University (left) and summer intern Jaycee Hall of the Akwesasne Mohawk Nation sample wetland soils at Brandy Brook, New York, during the flood year of 2017. Credit: Michael Twiss

The creation of the Moses-Saunders hydropower dam across the St. Lawrence River in the late 1950s provided an ongoing abundant supply of electricity, but the regulation of river flows it allowed constrained water levels on Lake Ontario and the upper St. Lawrence River unnaturally. As a consequence, cattail marshes proliferated at a time when atmospheric deposition of contaminants such as mercury was rampant. Cattail wetlands can purify waters, so their ecosystem service has been to accumulate mercury and other contaminants across the region.

The mercury present in river shoreline wetlands is a legacy of past coal burning for electricity generation and industry, which deposited this toxin across the landscape. The latest water level regulation plan for Lake Ontario and the St. Lawrence River seeks in part to restore a more natural diversity of plants in cattail-dominated wetlands. Since mercury is a harmful neurotoxin and can bioaccumulate in fish and humans, the key to understanding the impact of changing water levels on water quality will be to determine how fast mercury is released, where it goes, and in what form.

Researchers at Clarkson University in Potsdam, New York, in collaboration with scientists at the St. Lawrence River Institute of Environmental Sciences in Cornwall, Ontario, are investigating how changing water levels could impact water quality. As a Ph.D. student in the Environmental Science and Engineering program of Clarkson’s Institute for a Sustainable Environment, graduate student Evie Brahmstedt seeks to bridge the gaps in knowledge between environmental change and environmental policy.

“The new water level management plan for the St. Lawrence River is designed to reduce the extent of cattail wetland area by 29 percent with concomitant gains in wetland meadow and submerged aquatic vegetation. This will increase biodiversity in the river and support greater fish production,” Brahmstedt said.

Her 2016 study estimated that about 87 kilograms (190 pounds) of mercury will be mobilized with this change in wetland community structure. Changing water levels change the type of bacteria that are active in the wetland soils: some bacteria are able to convert mercury into methlymercury, the chemical form of this toxin that accumulates in higher organisms. Stimulating these bacteria may accelerate mercury moving from soils into the aquatic food chain.

With funding from the Great Lakes Research Consortium in New York and the Ontario Ministry of the Environment and Climate Change, the project was expanded in 2017 with Canadian partners to measure the threat of mercury in 80 wetlands in the river from Lake Ontario to the Moses-Saunders power dam.

Once researchers have a firm understanding of the extent of mercury content in these wetlands and the mechanisms by which it is mobilized, they can work with hydrologic engineers and ecosystem modelers to predict how much mercury will be mobilized and estimate if new fish guidelines need to be put in place. The project ends in 2019.

The work by Clarkston University and its partners seeks to know what the impact will be in the future so people can plan and adapt for it ahead of time. Informing the public of the risk is essential to limiting the damage from mercury exposure so that appropriate actions can take place, such as increased monitoring of fish mercury levels and revised fish consumption guidelines if necessary.

thousands islands lake ontario
Thousand Islands archipelago looking west to Lake Ontario. Due to more stable water levels following the regulation of flows through the Moses-Saunders hydropower dam in 1958, extensive cattail marshes have filled in shallow areas normally occupied by wetland meadows and submerged aquatic vegetation. Credit: Michael Twiss

Michael Twiss supervised the Brahmstedt study and is a Great Lakes limnologist in the faculty of Clarkson University, in Potsdam, New York, and a member of the IJC’s Great Lakes Science Advisory Board.

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