LIPID CLASS AND ALKANE DISTRIBUTION IN SETTLING PARTICLES OF THE UPPER LAURENTIAN GREAT-LAKES

Sediment traps were deployed at up to 6 depths at seven stations in Lakes Superior, Michigan, and Huron for 2 months during the summer of 1984. Total organic carbon, total lipid, lipid classes, and alkanes were measured in the collected material to gain information on the composition, sources, and fate of particulate organic matter in the Great Lakes. Total aliphatic hydrocarbon was a large component of all samples, accounting for more than 15% of the extractable lipids. Particles collected at 10-m depth in Lake Huron had especially high relative contributions (more than 65% of total lipids) of total aliphatic hydrocarbons at the three stations examined. The high proportion of aliphatic hydrocarbon appears not to have originated from customary pollution sources. The alkane distribution was strongly dominated by even-numbered carbon chains of unknown origin. Algae are a possible source for the unsaturated hydrocarbons that were present at relatively elevated levels in settling particles. Botryococcus braunii, sampled from Lake Michigan had as much as 80% of its lipids in the form of hydrocarbons. Wax and sterol esters constituted less than 10% of the lipids in trap material except in samples from mid-depths in Lake Huron where high levels of these compounds may have resulted from elevated amounts of calanoid copepod debris or swimmers entering the traps.