ANTHROPOGENIC IMPACTS ON LAKE ECOSYSTEMS: A PALEOLIMNOLOGICAL STUDY

Anthropogenic activities including deforestation, agriculture, and watershed development are known to affect the input rates of nutrients and organic matter into lakes, often increasing the overall productivity of lake biota. Typically, biological techniques are applied to address issues such as degrading lake ecosystem health. However, because the geochemistry of the organic fraction of lake sediments records perturbations to lake ecosystems, proxies such as %C, C/N ratios, and C-isotope composition of lake sediments also provide significant insights into a lake's response to environmental disturbances. An understanding of how human activities impact lake ecosystems is essential for environmental planners to effectively manage a watershed. The aim of this project is to assess to what degree elemental and isotopic analysis of lake sediments can be used as a proxy for specific, historically documented, human disturbances.

We have analyzed short (25-30 cm) sediment cores from three acidic and dystrophic Vermont lakes. %C, %N, C/N ratios, and delta 13-C were measured at 1cm intervals for each core. We have complemented the chemical analyses with a historical records search of the watersheds surrounding the study lakes, attempting to correlate specific human activities with the observed changes in the geochemical records. Additionally, the results of this study were compared to those obtained by a previous study of eleven VT lakes. Our preliminary results indicate an upcore increase in organic matter deposition (as indicated by %C and %N) in all three lakes. This, combined with a decrease in both sediment delta 13-C values and C/N ratios suggest an increase in algal productivity, likely caused by cultural eutrophication. Anthropogenic activities potentially responsible for such an increase in productivity include farming and shoreline development.