PRE AND POST SETTLEMENT NUTRIENT AND CONTAMINANT LEVELS IN LAKE SEDIMENTS, SPRING LAKE, MN

Humans have a large impact on the environment that surrounds them, including our lakes and waterways. I set out to find how people were affecting the nutrient and contaminant levels that were being introduced into Spring Lake, a hyper-eutrophic lake and part of a large watershed in Prior Lake, MN where water quality is a concern. To measure the amount of environmentally available phosphorus that was locked in the sediments I used a multi-step acid digestion method and then used ICP-AES to determine P, Pb, As and Fe concentrations. I also measured the total organic carbon and nitrogen concentrations in the sediments as well as doing smear slide analysis to figure out what type of environment and water conditions were present during the deposition of the sediments. Pb-210 dating allowed us to make age profiles for our concentrations and we discovered that in the 1920’s there began to be an increase in the accumulation rates of our elements of interest. The depositional rates of all of our elements of interest increased two to five times after the 1920’s. Phosphorus, the main element of focus, had an accumulation rate of .28 µg/cm²yr in 1885 and increased to 1.45 µg/cm²yr in 1982. This discovery correlates to when Europeans began to settle in the area and gives us a better understanding of how the development and growth of the urban area has affected the state of Spring Lake. With all this new information we can now understand how the nutrient and contaminant inputs have been affected in the past which will help the Prior Lake/Spring Lake watershed be able to manage it better in the future.