Dissolved organic carbon in lakes: effects on thermal structure, primary production, and hypolimnetic metabolism

Watershed characteristics determine the inputs of dissolved organic carbon (D O C) and nutrients into lakes. In-lake processes modify these inputs to determine lake characteristics. I examined the role of allochthonous DOC as a m aster variable that affects the thermal structure of lakes during summer stratification, primary production, ecosystem respiration, and dynam ics of the biota. I combined comparative studies, theoretical modeling, and ecosystem experiments to address the following questions: 1) Is light important in the interactions of algal biomass and DOC concentrations? 2) How does the input of allochthonous nutrients (which affects chlorophyll concentrations) and DOC (which determines water color) affect lake thermal structure? 3) What effect does DOC have on hvpolimnetic metabolism? 4) Do short-term fluctuations in food-web structure have long-term effects on lake nutrient dynamics and primary production?