The objective of this investigation is to determine the role of diagenesis in controlling the accumulation of carotenoid and chlorophyll pigments in lake sediments. The research plan includes both field data collection and laboratory experiments. The field approach involves measuring the concentrations of parent pigments and their derivatives in sediment traps and sediment cores from a group of contrasting lakes. Comparisons of sediment trap material and surface sediment cores from a group of contrasting lakes. Comparisons of sediment trap material and surface sediments will be used to evaluate the importance of oxygen status, sediment mixing, detritivore activity, and organic matter content in controlling diagenesis rates. Laboratory experiments involve production of 14C-labelled pigments using algal cultures, incubation of labelled pigments in sediments under aerobic and anaerobic conditions, and measurement of the rates and pathways of pigment degradation by sediment bacteria (aerobic and anaerobic) and a detritivore (chironomids). Methodology will include analysis of pigments and degradation products by HPLC and mass spectrometry and use of 210Pb to determine sedimentation rates, sediment mixing, and sediment focusing. Information on pigment diagenesis in lake sediments will facilitate using sediment pigment profiles to determine organic matter sources, changes in algal types and primary production, and to evaluate the role of organic matter cycling in controlling the chemical composition of lakes, all of primary importance to paleoenvironmental reconstruction of lake history and to understanding of how biomolecules develop into geomolecules.
