ISOTOPIC ANALYSIS OF SEDIMENTS AS A PROXY FOR ENVIRONMENTAL QUALITY IN TEMPERATE LAKES OF WISCONSIN

There is an increasing need for humans to address anthropogenic changes such as deforestation, eutrophication, and water pollution in our ecosystems. Stable isotopes preserved in lacustrine sediments are one way of reconstructing the environmental history of a region. Using this geochemical tool to better understand how humans affect lacustrine environments can facilitate management strategies for restoring biodiversity and essential ecosystem services lost due to human activity in the biosphere. Here, we use stable isotope analysis from temperate lakes in Wisconsin to highlight paleolimnological changes in response to increasing stress due to human activity.

Cores from Lake Monona and Shadow Lake provide a record of lacustrine responses to increased nutrient loading and other changes in the biogeochemical cycle after human settlement began in the mid-1800’s. We measured ¹³C/¹²C and ¹⁸O/¹⁶O ratios of organic and inorganic C (calcite) in the core sediments to infer decadal trends in nutrient loading and primary production at these sites. Our preliminary results indicate that d¹³C values from Lake Monona sediments 50-140cm below the sediment water interface oscillated in a natural pattern before decreasing sharply between 50cm and the surface of the lakebed. d¹⁸O values follow a similar, variable pattern until above 50cm, where values remain relatively constant. We hypothesize that the changes in d¹³C values are linked to increased nutrient loading and eutrophication from agricultural and urban development of the area. Changes in d¹⁸O values point to disruption of thermal stratification in the lakes and suggests a link to sudden climatic changes in the last century. These changes indicate that ecological stresses of anthropogenic origin warrant renewed management strategies that can return lacustrine environments to their natural state.