Influence of Stream-Lake Interactions on Nutrient Transport and Function of Aquatic Ecosystems: Modeling, 15N Experiments and Watershed Analyses

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The research will address three hypotheses arising from the spatial pattern of connectivity between streams and lakes: (1) lakes are nutrient sponges, absorbing spring nutrient pulses and then slowly releasing them over the summer, thus stabilizing biological production downstream; (2) lakes reduce biological productivity downstream because nutrients are lost via sedimentation and denitrification; (3) lakes are solar collectors, thus increasing watershed temperatures and the metabolic rates of organisms. These hypotheses will be addressed in sub-alpine watersheds in the Sawtooth Mountains of Idaho using: (a) hydrological and food-web modeling; (b) releases of a tracer nutrient (15NO3) followed through the food webs of a stream-lake-stream linkage, and; (c) analyzing patterns of chemical, thermal and biological activity in three watersheds with and three without lakes. The work will be useful for eutrophication and lake fertilization studies, for the protection of endangered fishes, and for the prediction of production in streams, rivers, and lakes.