Southeastern Section - 66th Annual Meeting - 2017

Paper No. 14-13
Presentation Time: 1:00 PM-5:00 PM


DANNEHL, John1, LEONARD-PINGEL, Jill1, MICHELSON V, Andrew2 and FALLS, Emily3, (1)Washington and Lee University, 204 W Washington Street, Lexington, VA 24450, (2)Division of Science, Engineering, and Technology, Thomas Nelson Community College, 4601 Opportunity Way, Williamsburg, VA 23188, (3)Geology Department, Washington and Lee University, 204 W. Washington St., Lexington, VA 24450,

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.