On April 11th, Dr. Dale Robertson of the U.S. Geological Survey (USGS), presented the USGS’s annual “State of Big Green Lake” to the GLSD Board of Commissioners and the Lake Management Planning (LMP) Team. The purpose of the meeting was for Dr. Robertson to provide an overview of the recent water quality in Green Lake, nutrient loading (specifically phosphorus) into the lake from the watershed, as well as provide an overview of his conclusions from the Lake Study recently completed by the USGS, Green Lake Association, and Michigan Technological University.
Approximately 70% to 90% of the tributary flow into Green Lake is monitored annually to determine nutrient loading. Utilizing monitoring data from 2012 to 2021, the GLSD has worked closely with our Lake Management Team partners to help fund over 140 BMPs throughout the watershed. These efforts, while costing upwards of $2 million dollars, have stopped approximately 5,800 lbs of phosphorus from entering Green Lake. Unfortunately, against the best efforts of the GLSD and our Lake Management Partners, weather and climate continue to be two of the main drivers behind nutrient loading into the lake. The following points were made by Dr. Robertson.
• Rainfall in the watershed in 2021 was back to normal after 5 successive years of very high levels. Precipitation in 2021 was roughly 20% less than during 2016-2020.
• However, the loading of phosphorus into the lake only decreased by roughly 10%, illustrating the impact that the timing, intensity of the rainfall, and antecedent soil moisture can have. This can be seen in runoff from spring rains on bare soil as well as the runoff from an intense rainfall event (2”+ rain events in 1 hour vs. ¼” rainfall over 1 hour).
• Modeling results from the Lake Study illustrated a need to reduce non-point source phosphorus loading to Green Lake to about 12,000 lbs/yr, which is a roughly 50% reduction from that in 2014-2018. This reduction is necessary for Green Lake to reach the midsummer total phosphorus goal of 15ug/L set forth by the Wisconsin DNR for a 2-story fishery lake.
• Based on USGS monitoring through 2021, the in-lake midsummer phosphorus concentration has averaged 18.2 ug/L over the past 5 years, with 2021 having a midsummer total phosphorus concentration of 18.9 ug/L.
Based on the results of this study and ongoing monitoring, there is much more work to do in the watershed. These activities will take millions of dollars provided by the Lake Management Partners and will take time to move the in-lake phosphorus levels down to 15 ug/L.
What is being done to help the water quality of Green Lake? The GLSD along with our Lake Management Planning (LMP) Team partners are working with the Wisconsin Department of Natural Resources (DNR) and local farm community to continually add best management practices (BMPs) to the watershed which are designed to keep phosphorus-laden soil out of the lake. To this end, the GLSD (in partnership with the Green Lake and Fond du Lac Counties’ Land Conservation Departments as well as the Green Lake Association) just applied for a $600,000 grant from the DNR to significantly ramp up our efforts in the watershed. This includes increased outreach into our agricultural community as well as funding new and critical programs such as our Green Lake Watershed Soil Health Program and our upcoming Watershed Buffer Program. Participation in these practices is voluntary for the agricultural community; we cannot be successful without their support. A big thank you to the Green Lake County Land Conservation Department staff for their assistance in shaping the grant application priorities and potential projects.
You can help be part of the Lake Management Process. The GLSD, along with our Lake Management Partners, are starting the multi-year process of updating our 2015 Big Green Lake Management Plan. This document is critical to the planning and prioritization of the work to be done in the lake and watershed. Components of this plan include critical issues such as aquatic plant and fisheries management strategies, protection of sensitive habitat areas, and goals for managing nutrient loading into the lake. As part of this 2-year process, the DNR requires lake managers to actively solicit public input and participation. This public outreach is a priority for the GLSD and our partner, the Green Lake Association. Please watch social media and/or our local paper for opportunities to provide your lake
management opinions.