On February 13, 2018, 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 at the regular board meeting of the GLSD. A summary of the USGS’s key updates are provided below.
USGS general conclusions for 2017:
• On a positive note, over the past twenty years, the percentage of phosphorus coming into our lake via various forms (streams,
runoff, etc) has decreased by 25% from 0.134 mg/L (1997-1998) to 0.103 mg/L (2013-2017).
• On a negative note, the last two years have been two of the wettest years on record, the heavy rainfall and subsequent runoff have had a negative impact on water quality (sediment and phosphorus loading) to all Wisconsin water bodies, including Big Green Lake.
• In late 2017, the GLSD Board of Commissioners approved changes to install monitoring stations on both White Creek and Hill Creek in addition to the existing monitoring stations for Silver Creek, Dakin Creek, Spring Creek, Roy Creek and Wurches Creek. These upgrades will allow us to use actual monitoring data/information for over 90 percent of the tributary waters coming into Big Green Lake on an ongoing basis. This data and information is critical to making important lake management decisions as well as measuring changes to the lake over time.
By way of background information, the USGS, in cooperation with the Green Lake Sanitary District (GLSD), has monitored Big Green Lake dating back to 2004 and its tributaries dating back to the 1980s. The USGS evaluates Big Green Lake’s tributaries to the lake to quantify nutrient loading to the lake. The USGS uses very consistent and rigorous sampling protocols that enable the water quality of the lake and its tributaries to be regularly evaluated and examined for short and long-term trends. GLSD’s annual contract with the USGS comes to just under $100,000 per year, twenty five percent is paid for by the federal government. Tributary monitoring identifies total phosphorus and suspended sediment concentrations entering the lake; while lake monitoring includes measurements for total phosphorus, dissolved nitrate plus nitrate-nitrogen, dissolved ammonia nitrogen, total Kjeldahl nitrogen, chlorophyll a, secchi (water clarity) and depth profiles for water temperature/dissolved oxygen/pH/specific conductance.