Author: Lindsay  Starr,  PhD Student (Wright State University)

Description:
Surprisingly little is known about the sources and cycling of bioaccumulative methylmercury (MeHg) in the watershed of Lake Erie, despite the lake having a world-renowned sport fishery.  We examined concentrations and fluxes of total mercury (Hg) and MeHg to western Lake Erie from the Detroit, Sandusky, and Maumee Rivers that drain a mix of urban and agricultural landscapes. We also measured the potential for MeHg production and demethylation in river water with incubation tests of enriched stable Hg isotopes. Average total Hg concentrations were remarkably similar in the Detroit (5.4 ± 0.8 pM) and Sandusky Rivers (5.3 ± 0.9 pM) and less than in the Maumee River (11.6 ± 2.8 pM). Similarly, MeHg was lower in the Detroit (0.38 ± 0.25 pM) and Sandusky Rivers (0.24 ± 0.13 pM) than in the Maumee (0.63 ± 0.46 pM). The mean fraction of total Hg as MeHg in water was comparable among the rivers (~5%), suggesting similar biogeochemical cycling in the three subcatchments. MeHg production potentials ranged from 0.27 to 0.32 day^–1  among rivers and MeHg demethylation potentials ranged from 0.79 to 0.88 day^–1. High potential rates of both transformations imply rapid cycling in river water during the summer. Estimated river fluxes of MeHg were much greater from the Detroit River (200 mmol day^–1) than from either the Maumee (1.5 mmol day^–1) or Sandusky Rivers (0.05 mmol day^–1). These preliminary results suggest that the Detroit River is a large fluvial source of MeHg to western Lake Erie and that much of the MeHg in river water during summer may be derived from in situ transformations. 

Category: Scientific Program Abstract > Special Session > CS07 Trace metals