High Five Project – Mercury in Minnesota Rivers

Fish consumption advisories exist for Minnesota water bodies due to mercury contamination. In this project we are examining hydrologic exchange between rivers and riparian areas in five systems. The five chosen rivers have the highest levels of mercury in game fish in the state of Minnesota. Another system with low levels of mercury in the fish was chosen as a contrasting system. We seek to determine if this exchange could be an important contributor of methylmercury burdens in fish.  We hypothesize that riparian areas may provide ideal conditions for the methylation of mercury and that ground water flow may be a significant input of methylmercury to many riverine systems. To test our hypothesis, we installed wells at multiple riparian locations to determine the direction of ground water flow. We also installed piezometers to allow us to sample water in multiple soil layers to assess methylmercury concentrations. Preliminary data suggest that porewaters in contact with the riverbed may be important areas of mercury methylation. Ground water methylmercury concentrations were highly variable amongst systems and no clear trends were observed to date.