SPATIAL AND TEMPORAL TRENDS OF POLYCYCLIC AROMATIC HYDROCARBON LOADINGS ACROSS THE STATE OF MICHIGAN

Previous works on large lakes, i.e. for the upper Great Lakes region, indicate atmospheric deposition as the key pathway for PAH loading; greatly influenced by local source emissions, e.g. the Chicago-Gary industrial complex. The underlying hypothesis is that PAH loadings have been reduced with emission legislation, leading to the evolution of a more well-mixed atmospheric system with reflection of a more regional pattern of deposition. Sediments from several inland lakes through Michigan were analyzed temporally for PAHs and Pb-210, attaining inventories and accumulation rates. If the hypothesis is true, (1) during peak concentration of PAH loadings a decreasing industrious south to north spatial depositional gradient will be observed, (2) a consistent regional signature will be observed. Corrected PAH accumulation rates and inventories were used to assess aerial accumulation of the upper Great Lakes region and their subsequent watersheds. The corrected inventories and correlating dates of initial appearance of PAHs show a spatial depositional gradient. The later, suggests northern migration of PAH onset over the region, influenced by local atmospheres rather than a regional pattern. PAH accumulation rates, concentrations and peak historical date trends do not follow the regional pattern indicating local watershed influences.