The Delavan Lake Quality Goals - Nutrient and Clarity Measurements

The current goals for Delavan Lake water quality were established as part of a University of Wisconsin Water Resources Management Workshop conducted in 1986. However, they are currently being re-evaluated based on updated conditions. 

Current Lake Quality Metrics - 

Phosphorous - 34ug/L

Chlorophyll - 15ug/L

Secchi Depth - 1.5 Meters

Proposed Lake Quality Metrics - 

Phosphorous - TBD (est. between 24 and 30 ug/L)

Chlorophyll - TBD

Secchi Depth - 3 Meters

Background...

On November 9, 2020, members of the Town of Delavan Lake Committee met to discuss the quality metrics that are used to measure the health of the lake. The current goals that were set back in the late 80’s/ early 90’s when the lake was being rehabilitated. Now that Delavan Lake has established a new equilibrium teetering on impaired, new goals are being explored. Here is a summary of that meeting:

  • Secchi depths averages were reviewed.

  • It was discussed how the June Secchi Depth skews the entire summer’s results and goal evaluation.

  • Dale Robertson (Scientist with the USGS) ran a quick analysis demonstrating the impact of including June in “summer”.

  • The meeting attendees are recommending to the Lake Committee to change the “summer” Secchi depth goal months to be July, August, and September and to increase the Secchi Depth goal to 3 meters.

  • It was discussed how the zebra mussel population, although invasive, does positively impact the Secchi Depth and that zebra mussels are a new normal of the lake.

  • As such, the Secchi Depth goal should be adjusted for this impact, along with the fact that improving Secchi Depth has been shown to increase property values / grow economic activity and is a enjoyed by those using the Lake.

  • Another aspect to look at for Secchi depth would be take measurements closer to the shoreline not just in the deep waters.

  • There was a discussion about algae (how types/sizes have changed) and how the fishery impacts this. •

  • Chlorophyll and Phosphorus goals were reviewed.

  • Robertson estimated that with adjusting the Secchi Depth goal to 3 meters, that the Chlorophyll and Phosphorus targets would then be Phosphorus

Complete Subcommittee Minutes...

November 9, 2020 @ 4pm

Minutes

 

Attendees: Katherine Gaulke (Lake Com Chair), Dan Lemanski (Lake Com), Richard Beers (Lake Com & DLSD), Leo Dietlin (Lake Com), Jim DeLuca (DLSD), Charlie Handel (DLSD), Kim OKeefe (DLSD & DLIA), Sue Heffron (DLIA & Kettle Morraine Land Trust), Justin Poinsatte (SEWRPC), Dale Buser (SEWRPC), Dale Robertson (USGS), Glenn Dickow (Delavan Lake Advocate)

 

The Subcommittee recommends to the Lake Committee to set the Secchi Depth goal at 3 meters. With June being looked at on its own via weekly measurements to identify trends in Algal blooms (weather, heat, wind, etc) and then averaging July, August, and September to align with DNR.  The USGS does one monthly measurement and then uses the DLSD weekly measurements for other data points from the middle of the lake.

 

The Subcommittee further recommends that the Lake Committee / Town contract with USGS to conduct modeling to determine new phosphorus and chlorophyll goals based on the 3 meter Secchi Depth Goal. The hope is that when the new phosphorus goal is achieved it will move Delavan Lake off the impaired list (30 ug/L), and move towards at least 24 ug/L for phosphorus.  SEWRPC requests that the modeling and new goals be set by end of January 2021.  Dale Robertson (USGS) to provide a quote for the Lake Committee to review. 

 

SEWRPC will then use these updated goals to make phosphorus load recommendations and BMP recommendations by municipality and estimate costs and impact of recommendations with the understanding that the Town only has control within its boundaries; divide out the recommendations into each municipality in the watershed - what could each municipality do to improve Delavan Lake Health. SEWRPC will look at storm water, farm, and urban runoff for possible recommendations on where to do BMPs and projects to protect Delavan Lake and achieve the new lake goals. 

 

Additionally SEWRPC will discuss the fishery and carp removal and make recommendations. And will look at boat traffic/capacity. Gaulke to get the buoy maps to SEWRPC pack for analyzing lake capacity. 

END OF MINUTES...

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