Diagenesis of Organic Matter in the Sediments of Lakes Ontario,Erie, and Huron

The organic matter in the modern sediments of Lakes Ontario, Erie, and Huron is composed of humic compounds (68 to 83%), amino acids (19 to 20%), lipids (2 to 8%), carbohydrates (2 to 6%), and amino sugars (0.5 to 4%). Amino acid and carbohydrate concentrations are high in plankton samples, which are the primary source of the sedimentary organic matter. These compounds are decomposed during their passage through the food chains and while resting at the sediment-water interface with the concurrent formation of humic compounds. The degree of diagenesis of the modem sedimentary organic matter is related to both the trophic state of the lake and to the water depth, with the greatest amount in the most eutrophic lake basins and in the shallowest water depths. Diagenesis of the organic matter is rapid prior to burial in the sediments and is slow after burial. The decomposition rates of the sedimentary organic matter are in the following order: amino acids>>amino sugars>carbohydrates>humic compounds>lipids.