Engstrom, D. R.. St. Croix Watershed Research Station, dre@tc.umn.edu
Swain, E. R.. Minnesota Pollution Control Agency, edward.swain@pca.state.mn.us
Balogh, S. J.. Metropolitan Council Environmental Services, steve.balogh@metc.state.mn.us

 
ELEVATED MERCURY INPUTS TO URBAN LAKES FROM LOCAL EMISSION SOURCES AND WATERSHED RUNOFF: EVIDENCE FROM DATED SEDIMENT CORES FROM 50 MINNESOTA LAKES
 
Increased mercury inputs to lakes may result from changes in atmospheric Hg deposition, land-use changes that alter Hg retention in the watershed, or both factors simultaneously. In this study we analyzed historical Hg accumulation rates in lead-210 dated sediment cores from 50 Minnesota lakes to determine whether Hg loading to lakes in urban areas has increased more than in rural areas, and if so whether because of (1) proximity to local Hg emission sources or (2) enhanced delivery of atmospheric Hg in runoff from urbanized watersheds. Present-day Hg accumulation and Hg-flux ratios (modern:preindustrial Hg accumulation) increased with the proportion of watershed area under urban or agricultural land-use, and Hg-flux ratios were tightly correlated with erosional intensity as measured by the accumulation of detrital silicates in the sediment cores. Hg loading to urban lakes is thus enhanced by soil erosion and possibly runoff from impervious surfaces. Present-day Hg loading from direct atmospheric deposition, calculated by normalizing Hg-flux ratios to silicate accumulation, is about 35% greater in urban than rural areas. Hg loading to urban lakes was about 40% higher than present during the 1970s, and much of the ensuing decline can be attributed to elimination of local Hg emission sources.
 
Day: Friday, Feb. 5
Time: 03:30 - 03:45pm
Location: Sweeney Center
 
Code: CS63FR0330S