Lake of the Woods Historical Nutrient Project
Update from Mark Edlund, Senior Scientist, St. Croix Watershed Research Station
Work by partners at the Science Museum of Minnesota's St. Croix Watershed Research Station and the Minnesota Pollution Control Agency continued in southern Lake of the Woods through the summer of 2016. This group has been combining analysis of sediment cores to determine the history of nutrients and algae in Lake of the Woods with high frequency monitoring of water quality in summers of 2015 and 2016. A key part of this research is to find out how "legacy nutrients" from previous decades of pollution, may be stimulating algae blooms today.
Water quality buoys have been deployed in Muskeg Bay and two locations in Big Traverse Bay and are collecting data on water temperature and dissolved oxygen every 30 minutes. Last year's data showed that southern Lake of the Woods stratified 4-5 times during the summer creating a thermocline in the water column and causing dissolved oxygen levels in the bottom waters to plummet. When that happens, phosphorus is released from the sediments into the bottom waters, and when the wind blows strong enough to destroy the thermocline, those nutrients trigger algal blooms that have become commonplace in late summer and fall throughout the lake. This mechanism for triggering blooms had not been documented previously based on standard monitoring approaches that visit the lake at monthly or fortnightly intervals. Other work on the lake by this group included winter limnology to determine temperature and oxygen levels below the ice in Big Traverse Bay. Reduced oxygen levels in the bottom waters came as a surprise as the scientists tried to work in -27C temperatures. For more information see the the Science Museum of Minnesota's Field Notes website: www.smm.org/scwrs/fieldnotes