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Estimation of a Historic Mercury Load Function for Lake Michigan using Dated Sediment Cores
Citation:
ROSSMANN, R. Estimation of a Historic Mercury Load Function for Lake Michigan using Dated Sediment Cores. Presented at 52nd Annual Conference on Great Lakes Research (IAGLR), Toledo, OH, May 18 - 22, 2009.
Impact/Purpose:
To research results
Description:
Box cores collected between 1994 and 1996 were used to estimate historic mercury loads to Lake Michigan. Based on a kriging spatial interpolation of 54 Pb-210 dated cores, 228 metric tons of mercury are stored in the lake’s sediments (excluding Green Bay). To estimate the time variation of mercury flux to the lake, a core from one of the stations was selected to represent the time variation of mercury loads to the lake. Selection was based mixed layer thickness, sedimentation rate, location relative to major mercury sources, and a time variation of flux representative of that seen in all cores. For the selected core, the sum of the mercury mass within the core between 1850 and 1994 was set equal to the mercury storage in the lake. The kg/y for each dated interval of the core was then calculated. Missing years were obtained by linear extrapolation between the core intervals. The load calculated for 1994 was 1157 kg/y. This was significantly higher than the observed load of 768 kg/y. The observed mercury loads are believed to be biased low due to the sparse number of atmospheric deposition stations and lack of shoreline erosion fluxes. The flux in 1994 was the lowest it has been since 1892.