MP6 Mercury in Stream Ecosystems
202 Oregon Ballroom
1:20 PM - 4:40 PM, Monday
() Enhanced Methylmercury Export from an Experimental Wetland Following Sulfate Addition.
Monson, Bruce1, Swain, Edward1, Engstrom, Daniel2, Almendinger, James2, Jeremiason, Jeff3, Kolka, Randy4, Nater, Edward5, 1 Minnesota Pollution Control Agency, St. Paul, MN, USA2 Science Museum of Minnesota, St. Croix Watershed Research Station, Marine on the St. Croix, MN, USA3 Gustavus Adolphus College, St. Peter, MN, USA4 USDA Forest Service - North Central Research Station, Grand Rapids, MN, USA5 University of Minnesota, St. Paul, MN, USA
ABSTRACT- Wetlands are sites of mercury methylation and sulfate-reducing bacteria are considered the primary methylators of mercury. Previous laboratory and field mesocosm studies have demonstrated an increase in methylmercury (MeHg) levels in sediment and peatland porewaters following additions of sulfate. In this ecosystem-scale study, sulfate was sprayed onto half of a 2-ha experimental peatland at the Marcell Experimental Forest in northeastern Minnesota (USA), increasing the annual sulfate load by approximately four times relative to the control half of the wetland. Sulfate was added on four separate occasions during 2002 and delivered via a sprinkler system constructed on the lower half (1.0 ha) of the wetland. MeHg. total mercury, and other water chemistry analyte levels were monitored in porewater and at the outflow from the wetland. In addition, adjacent watersheds were monitored for mercury and other ancillary water chemistry. MeHg concentrations in flow from the wetland increased following each addition. Prior to the first sulfate addition, porewater MeHg concentrations (filtered, 0.45 
m) were not statistically different between the control (0.47 ± 0.10 ng/L, n=12; mean ± one standard error) and experimental 0.52 ± 0.05 ng/L, n=18) halves. Two weeks after the first addition in May 2002, MeHg porewater concentrations in the control half had not changed significantly, while the treated half increased to 1.63 ± 0.27 ng/L, a three-fold increase. Subsequent additions of sulfate in 2002 did not raise porewater MeHg, but MeHg in the treated half remained elevated relative to the control. Over the six months (May through September, 2002) when three sulfate treatments were applied to the peatland, MeHg export increased 23 to 34 percent over the predicted export if additional sulfate had not been added. These results demonstrate that sulfate increases MeHg concentrations within the wetland and in outflow from the wetland.
Key words: sulfate, methylmercury, wetlands, Minnesota