SOURCES OF MERCURY TO MICHIGAN'S INLAND LAKES

Limiting the release of mercury from industrial sources and more fully understanding the transport of mercury in the environment are required to improve ecosystem and human health. Lake sediment cores record both release of mercury from industrial sources and the watershed transport of mercury; however, the mixture of sources makes interpretation of the sediment record difficult. Dated lake sediment cores from 28 Michigan lakes were used to test the hypothesis that local sources of mercury, including industrial emissions and watershed disturbances, are significant contributors of mercury to the lake ecosystem. Anthropogenic mercury inventories indicate that inland lakes of Michigan are similar to the North American Great Lakes, evidence of a regional source. However, variability in anthropogenic inventories among geographically proximal lakes suggests a local-scale source. Temporal trends of focusing-corrected anthropogenic accumulation rates suggest sub-regional sources of mercury which may be related to coal combustion in the Great Lakes Region. Superimposed on the sub-regional pattern of mercury accumulation are episodic loading events. Episodic loading events are prevalent in all lakes and often common among lakes. Episodic events that are common among lakes could often be related to historical mercury consumption maxima or natural disasters. Episodic events that are unique to a lake may suggest a local-scale source. In several lakes focusing-corrected accumulation rates are increasing in the last decade. Those lakes in which mercury focusing-corrected accumulation rates are increasing are not located near major coal-burning power-generating facilities. This suggests that the increase may be due to a more local-scale source. Analyses of mercury emission inventory data also support a local-scale source hypothesis. Multivariate statistical models of GIS delineated land use features and land use/land cover provides insight into local-scale sources of mercury. For example, anthropogenic mercury accumulation rates are correlated to watershed:lake area ratio, sulfate deposition, and wetlands within 100 m of the lake.