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Global concentrations of atmospheric nitrogen have increased dramatically over the last 150 years.  While the effects of nutrients, particularly phosphorus, on aquatic systems are well known, the increase of atmospheric nitrogen to these aquatic systems remains unclear.  This increased in nitrogen has been attributed to rapids shifts in the biota of aquatic systems across the globe particularly in high latitude regions. We are looking at lakes in Sweden along a nitrogen gradient and examining fossil diatoms to determine the effect(s) of augment nitrogen on these communities Given the sensitivity of diatoms to environmental change, examination of lake sediments can provide clues as to the conditions of the lake at a certain period of time. Environmental reconstructions using diatoms found in lake sediment cores provide valuable information regarding natural fluctuations in the past including nutrients, temperature, pH, lake turbulence and ultra violet light. These paleo analyses allow for comparisons to present conditions and offer predictions of lake conditions under future nutrient scenarios. Preliminary results indicate major shifts in diatom community structure over time and declines in diatom species richness over the last 150 years. These results may provide insight into the trajectory in which these lake communities may proceed as the result of industrialization and a changing climate and may be applicable to other freshwater ecosystems experiencing nutrient shifts.

This work is supported by a New Faculty Grant from UW-SP University Professional Development Committee (UPDC) and a UW-SP Undergraduate Educational Initiative Grant.

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