Twin Cities WRS Seminar

Land Management and Phosphorus Budget in Wisconsin's Big Green Lake Watershed


Anita Thompson
University of Wisconsin, Madison

November 20, 2020


Big Green Lake (BGL) is the deepest natural inland lake and holds the second largest volume of freshwater in Wisconsin. The BGL HUC 10 watershed covers 277 km2 spanning Green Lake (58%), Fond du Lac (41%), and Winnebago (1%) Counties and drains through seven major tributaries and two major wetlands before discharging to the lake. Land use in the watershed is primarily agricultural (65%) with the balance in forests, wetlands, open water, and urban areas. In 2014, the WI Dept. of Natural Resources (WDNR) listed BGL as a 303(d) impaired water body because it fails to meet water quality criteria for dissolved oxygen caused by phosphorus (P) loading associated with agricultural runoff. Major watershed management efforts to reduce P loading to the lake have included BMP implementation, wastewater treatment plant upgrades, and restoration activities in the two major wetland systems. Despite these extensive efforts, BGL is now eligible to be impaired also for P based on the WDNR criteria of 15 mg/L. To guide lake and watershed management, we are conducting a P mass balance for the BGL watershed for the past 30 years combined with paleolimnological analysis to quantify amounts and locations of “legacy P” which may be acting as diffuse and long-term sources of P to the lake.

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Meeting ID: 943 2193 2246
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