Because of human intervention, the amount of atmospheric nitrogen deposited into alpine lakes has doubled in the last century. This alteration in aquatic nutrient concentrations may have been accelerated by increased precipitation in these regions. This study investigates the effects of nitrogen deposition and climate change on the community composition of sedimentary diatoms in montane lakes of Colorado and Montana. The interactions between anthropogenic nitrogen and precipitation are complex and their effects on diatom communities probably vary regionally. This project will use in situ experiments and field surveys to test the hypothesis that changes in the ratios of nutrients (e.g., nitrogen, phosphorus) have altered the structure of aquatic communities. Furthermore, the research will integrate paleobiology of fossil diatoms and elemental analysis, to reconstruct the composition of ancient communities, and the resources available to them. This study has potentially broad implications for understanding global change, and the mechanisms causing rapid shifts in the community structure of aquatic ecosystems.
