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 Ontario contribute to the record of changes in the lake watersheds and aquatic ecosystems which have resulted from European settlement and cultural eutrophication of these systems over the past two centuries. Compositions of n-alkanes and n-alkanoic acids extracted from lake sediments track the clearing of the original natural forests and the appearance of agriculture in the watershed areas beginning about 1820. Aquatic productivity increased as runoff of soil nutrients increased. Cultural eutrophication in the 1950s is recorded in increases in organic C and in n-C-17 alkane concentrations. Diagenetic effects overprint source changes as shorter chain length and unsaturated lipid components are preferentially removed from the sedimentary record.