Dissolved Oxygen Study for Green Lake
Green Lake is a treasured lake of statewide significance. Measuring 236 feet at its greatest depth, it is the deepest natural inland lake in Wisconsin whose pristine waters and diverse ecology have been revered by many.
But with great depth, comes great responsibility.
In 2014, the Wisconsin Department of Natural Resources (WDNR) classified Green Lake as an impaired waterway due to a band of low dissolved oxygen at certain lake depths—the likely but unproven culprit being high concentrations of phosphorus.
“Green Lake was listed as impaired [because] the thermocline, which is about 30 feet from the water surface, goes without oxygen for 7-10 feet within the summer months,” explained Ted Johnson, Lake Biologist with the WDNR and member of the Lake Management Planning (LMP) team.
It takes approximately 21 years for one drop of water to circulate throughout Green Lake. With such a slow retention time, phosphorus, sediment and other nutrients can exist within Green Lake for long periods of time, making water quality improvements a slow and steady process.
Since Green Lake’s impairment classification, the Green Lake Association (GLA) and members of the LMP team have been working in a proactive, meaningful way to address and reverse Green Lake’s water quality issues before they become a critical issue over the long-term.
Together, they are taking a science-based approach to understand Green Lake’s water quality issues before tackling them with long-term, science-based solutions.
In 2015, the GLA funded a Phase I research study to better understand the issues pertaining to Green Lak
e’s impaired status. Continuing this lake management momentum, the GLA was recently awarded a $200,000 WDNR grant to conduct Phase II of this rigorous effort. The ultimate goal is to improve the lake enough to meet optimal water quality goals and to be able to declassify it as an impaired water body.
Set to begin in the fall of 2016, the Dissolved Oxygen Study will be conducted in partnership with the United States Geological Survey (USGS), the WDNR, and the GLA with significant contributions from the Green Lake Sanitary District.
Beginning in 2017, those recreating near Daychola on the north side of the lake will notice two buoys taking continuous lake health readings. “This study will take into account the biological and chemical factors contributing to this phenomenon of low dissolved oxygen,” said Johnson.
While Green Lake’s band of low dissolved oxygen is linked to high nutrient concentrations, primarily phosphorus, the size and scale of these reductions are unknown.This research will develop evidence-based management strategies and phosphorus reduction requirements to achieve Green Lake’s water quality goals.
“This is a very important first step to understand the mechanisms that cause this band of low oxygen to exist. It’s a multi-year study at a PhD level and just a very exciting time to be conducting a study of this type,” remarked Johnson.
Understanding that Green Lake’s water quality issues will not be fixed overnight, the GLA and its lake partners are anxious to embark on this first step in addressing the complex issues related to Green Lake’s impairment and restoring it to meet water quality standards once again.