SOURCES, DEGRADATION AND RECYCLING OF ORGANIC-MATTER ASSOCIATED WITH SINKING PARTICLES IN LAKE-MICHIGAN

Sediment trap material collected at five depths from two locations in Lake Michigan has been studied to determine the sources of particulate organic matter and the early diagenetic changes which occur during sinking of particles. Aquatic material dominates in shallower depths whereas land-derived material is more important in near-bottom depths. Organic carbon concentrations decrease with depth as a result of remineralization of organic matter by microbial activity and dilution by resuspended bottom sediments. Preferential remineralization of algal organic matter and downslope transport of particulate matter from coastal areas create differences in the lipid biomarker characteristics of settling particles found at different depths in the water column. Calculations of apparent decomposition rate constants from lipid distributions at different depths show that shorter chainlength n-alkanoic acids are degraded faster than longer components. Carbon and nitrogen isotopic compositions of total organic matter are nearly unaffected by large-scale amounts of remineralization during sinking.