LAND USE AND URBANIZATION: CONTAMINANT TRENDS IN LAKE CORE SEDIMENTS OF LAKE PALMER AND LAKE HARRIET IN MINNEAPOLIS, MINNESOTA

The U.S. Geological Survey (USGS) is working with the National Water Quality Assessment program to complete a national study on lakes, reservoirs, and their watersheds. For over 10 years the USGS in Austin, Texas, has been studying the effects of urbanization on watersheds. Lake coring and paleolimnology have been used to better understand how water quality has changed within watersheds. This project focused on two lakes in Minneapolis, Minnesota: Lake Palmer and Lake Harriet. Each lake has very different land usages and urban development impacting its watershed. Lake Palmer is composed of two lobes, referred to as the east and west lobe. The east lobe has a pristine watershed with no urban development; this lobe represents a “reference” lake. In contrast, the watershed of the west lobe has undergone rapid urban sprawl over the past 50 years, representing “new urban”. Lake Harriet was urbanized in the early 20th century; this watershed represents “old urban”. The two lakes are used in this study to compare the impact of different amounts and timing of urbanization. Lake cores were retrieved from Lake Harriet and both lobes of Lake Palmer in 1997. The deposited sediment was analyzed for organochlorine compounds (OCs), metals, radionuclides, and polycyclic aromatic hydrocarbons (PAHs) to investigate trends with land use and urbanization. The results demonstrate that water quality in Lake Harriet and the west lobe of Lake Palmer have been impacted by urban growth. Levels of DDT, PCBs, and lead increased with urbanization. The decrease in concentrations resulted from bans on leaded gasoline and use of DDT and PCBs. In contrast, concentrations of metals and chemicals in the east lobe of Palmer are low and unchanging, correlating to the lack of urbanization in the watershed. A more complex relationship is seen with PAHs, which have been steadily increasing. The increase is still being researched, but results have shown a clear correlation with increased urban sprawl.