HISTORY OF THE COMPOSITION AND SEDIMENTATION OF TWO LAKES IN THE COMFORT LAKE FOREST LAKE WATERSHED DISTRICT IN THE LAST 200 YEARS

In the past decade, the Comfort Lake Forest Lake Watershed District (CLFLWD) started conducting lake core studies to understand the long-term health of the lakes in the district. We are collaborating with St. Croix Watershed Research Station and the CLFLWD to examine past and present lake health on multiple lakes of concern. One core was taken from Bone Lake and another from nearby School Lake in March and May of 2019, respectively. Lead-210 age- dating was conducted to determine the age chronologies of the two cores taken. A Loss-On-Ignition (LOI) analysis was conducted to determine the mass accumulation rates of organic, inorganic, and carbonate matter. The accumulation rates for Bone Lake increased nearly seven times their pre-European settlement levels by the 1930s. Meanwhile, School Lake’s accumulation rates doubled from the 1920s to 1950s. There is a clear increase in mass accumulation rates for both lakes in the post European settlement era, but the specific magnitude and timing of these changes differs for each due to the timing of land clearing, farming, and construction of new infrastructure at each lake. In addition to the cores, routine water column monitoring was explored. During summer 2019, School Lake showed a steep drop to low dissolved oxygen levels in fairly shallow water depths, making it harder for aquatic organisms to survive. Bone Lake, in contrast, saw a more normal profile for dissolved oxygen. We will continue to investigate the cores nutrient levels and water quality of Bone, School and other possibly impaired lakes to help the CLFLWD decide where to allocate their resources.