Water Levels May Impact Mercury Cycling in Upper St. Lawrence River Riparian Wetlands

Session: 30. - Ecosystem Impacts of the Lake Ontario-St Lawrence River Flood of 2017

Evie Brahmstedt, Clarkson University, [email protected]
Hao Zhou, Clarkson University, [email protected]
Erin Eggleston, Middlebury College, [email protected]
Thomas Holsen, Dept. Civil & Environ. Eng., Clarkson University, [email protected]
MacKenzie E. Waller, St. Lawrence River Institute of Environmental Sciences, Cornwall, Ontario, [email protected]
Matthew Windle, St. Lawrence River Inst., [email protected]
Jeff Ridal, St. Lawrence River Institute, of Environmental Sciences, [email protected]
Michael Twiss, Clarkson University, Dept. of Biology & Great Rivers Center, [email protected]

Abstract

The International Joint Commission has enacted Plan 2014, in order to improve biodiversity in the Upper St. Lawrence River (USLR). If the dominant macrophyte, Typha, is reduced in abundance, there is potential for wetland hydric soils, containing mercury (Hg), to become mobilized into the food web. Hg becomes hazardous if mercury-methylating microbes (MMMs) are present. The USLR has historically been impacted by sulfur and Hg deposition and accumulation of P. Here, the capacity of USLR wetlands to support MMMs was determined by quantifying total mercury, organic matter, C, N, S, P, and microbial communities in wetland soils in a 2016 preliminary study.  We estimate mobilization of 87 kg of Hg will result from the expected 29% loss of Typha marsh. To refine the prediction of the Hg threat, the project expanded to include 80 wetlands along the US and Canadian shoreline from the Thousand Islands region to fluvial Lake St. Lawrence in the summer of 2017 during a period of flooding. The comparison between flood and non-flood years illuminates impacts to wetland Hg cycling, which may influence biodiversity. Potential impacts to fish populations and other wildlife from enhanced Hg bioaccumulation need to be considered.

1. Keyword
mercury

2. Keyword
wetlands

3. Keyword
St. Lawrence River

4. Additional Keyword
Hydric soils