Identification of Methylmercury Export Hotspots in an Industrially-Influenced Great Lakes Coastal Wetland

Abstract

The production and export of methylmercury (MeHg) is a critical first step to accumulation of mercury (Hg) in the lower food web and subsequent magnification in game fish. The purpose of this thesis was to identify areas of MeHg production and export in a freshwater estuary with a history of industrial influence by using ecological boundary delineations. Sediment, porewater and surface water was collected over two seasons from eleven sites encompassing four high-carbon sheltered embayments, two intermediate-carbon clay-influenced bays, and five low-carbon industrially influenced bays in the St. Louis River Estuary (Duluth, Minnesota). Ecologically delineated areas contained characteristically different quantities of Hg and MeHg and appear to be a useful framework for identifying locations likely to experience a net production of MeHg. The results provide a basis for understanding how MeHg can move through freshwater aquatic environments with complex hydrogeochemistry and could form the basis for effective resource management decisions.