Depositional controls on lacustrine sedimentary organic geochemistry

This study was designed to examine the relationship between depositional environment and sedimentary organic geochemistry in modern lacustrine systems, and to identify the relative significance of the various processes that control sedimentary organic matter (OM). The most significant difference in total organic carbon (TOC) content in surface sediments (∼15%) was observed between two lakes, which is interpreted to be primarily the result of higher levels of productivity due to highly efficient nutrient recycling. Intra-basinal effects of primary productivity on sedimentary OM within the basins examined in this study were much less pronounced than the inter-basinal differences (∼1%). Enhanced preservation of detrital OM may increase sedimentary TOC content by approximately 0.5--1.5% and have a minor effect on the type of OM preserved. Dilution of sedimentary OM by inorganic material may account for approximately 0.5--2.0% of the TOC range found in surface sediments of the lakes studied. The effect of inputs of terrestrial sediment on the organic character of surface sediments in these lakes is highly variable, and is most significant at the depositional environment level. The resuspension and redeposition of terrestrial sediment may account for significant amounts of OM deposited in offshore regions of lacustrine basins. This process effectively separates denser mineral sediment from less dense OM and allows terrestrial OM to preferentially be transported farther offshore. The net result for the sedimentary organic geochemistry in these regions is to maintain relatively high TOC contents with a mixed terrestrial-lacustrine geochemical. This hydrodynamic separation of mineral and organic constituents is most pronounced in regions with shallow bathymetric gradients.; Aliphatic biomarker concentration and compound-specific stable carbon isotopic composition data from surface sediments in Lake Bosumtwi were used to quantitatively constrain the sources of sedimentary OM in this system. Principal component analysis (PCA) was performed on these data, and synthetic chromatograms were constructed from the PCA results combined with the raw data to identify the chemical parameters that contribute most significantly to the variance of the dataset. Although this approach failed to produce a more reliable indicator of OM source in the lake sediments, the method was validated and suggestions for improvements are proposed.