LAKE CORE HISTORIES OF HUMAN IMPACTS ON TWIN CITIES METRO AREA LAKES OVER THE LAST TWO CENTURIES

Urban and suburban lakes face human impacts in the form of nutrient loading, contamination, and increased sediment levels. As part of a collaborative watershed management project we explored the recent histories of several lakes in the Twin Cities Metro Area (TCMA), Minnesota. The overall goal of this ongoing project is to use the information from these histories to target the lakes with best prospects for restoration. In this presentation we share results of sedimentary geochemical work (X-ray fluorescence (XRF), Loss on Ignition (LOI), Total Organic Carbon (TOC), and Carbon/Nitrogen (CN) analysis) on sediment cores collected from the lakes to explore the change since the time of European settlement (Ca. 1860 A.D.) of the Comfort Lake Forest Lake Watershed District in the northern TCMA. All of the lake core records have detailed age profiles from ²¹⁰Pb age dating. All of the lakes show recognized changes in sedimentation rate and bulk chemistry of the sediments after European settlement, but the timing differs between the different lakes. These lakes vary in size and in the level of development around them, so we also discuss local variability specific to individual lakes in terms of their levels of nutrients and contaminants through time.