SEDIMENTARY GEOLIPID RECORDS OF HISTORICAL CHANGES IN THE WATERSHEDS AND PRODUCTIVITIES OF LAKES ONTARIO AND ERIE

The organic matter contents of sediments deposited in Lakes Erie and O ntario contribute to the record of changes in the lake watersheds and aquatic ecosystems which have resulted from European settlement and cu ltural eutrophication of these systems over the past two centuries. Co mpositions of n-alkanes and n-alkanoic acids extracted from lake sedim ents track the clearing of the original natural forests and the appear ance of agriculture in the watershed areas beginning about 1820. Aquat ic productivity increased as runoff of soil nutrients increased. Cultu ral eutrophication in the 1950s is recorded in increases in organic C and in n-C-17 alkane concentrations. Diagenetic effects overprint sour ce changes as shorter chain length and unsaturated lipid components ar e preferentially removed from the sedimentary record.