Flux of Total and Methyl Mercury to the Northern Gulf of Mexico from U.S. Estuaries

Chad R Hammerschmidt, Wright State University Main Campus, Dayton, OH, United States, Clifton S Buck, Skidaway Institute of Oceanography, Savannah, GA, United States, Katlin L Bowman, University of California Santa Cruz, Santa Cruz, CA, United States, Gary A Gill, Pacific Northwest National Laboratory, Richland, WA, United States and William M Landing, Florida State University, Earth, Ocean, and Atmospheric Science, Tallahassee, FL, United States
Abstract:
To better understand the source of elevated methylmercury (MeHg) concentrations in Gulf of Mexico (GOM) fish, we quantified fluxes of total Hg and MeHg from 11 rivers in the southeastern United States, including the 10 largest rivers discharging to the GOM. Filtered water and suspended particles were collected across estuarine salinity gradients in Spring and Fall 2012 to estimate fluxes from rivers to estuaries and from estuaries to coastal waters. Fluxes of total Hg and MeHg from rivers to estuaries varied as much as 100-fold among rivers. The Mississippi River accounted for 59% of the total Hg flux and 49% of the fluvial MeHg flux into GOM estuaries. While some estuaries were sources of Hg, the combined estimated fluxes of total Hg (5200 mol y-1) and MeHg (120 mol y-1) from the estuaries to the GOM were less than those from rivers to estuaries, suggesting an overall estuarine sink. Fluxes of Hg from the estuaries to coastal waters of the northern GOM are approximately an order of magnitude less than atmospheric deposition fluxes.
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