Before the treatment started, Barr Engineering collected water samples from Spring Lake and measured total phosphorus and Chlorophyll-A. Monitoring chlorophyll levels is a way to track algae blooms. Surface waters with lots of algae are typically high in nutrients, like phosphorus and nitrogen; that’s why it’s also important to measure phosphorus, because phosphorus drives algal growth. For reference, lakes like Spring are not supposed to exceed 40 micrograms per liter (µg/L) for total phosphorus and 14 µg/L for Chlorophyll-A in Minnesota.
Prior to the treatment, Barr recorded 220 µg/L of total phosphorus and 45.5 µg/L of Chlorophyll-A for Spring Lake. On November 1st, following the alum treatment, Barr measured 59 µg/L of total phosphorus and Chlorophyll-A concentrations of 4 µg/L, which indicate a significant drop in phosphorus and chlorophyll concentrations. While these initial results are positive, the real test will come next spring when the lake has to compete with spring runoff and warming temperatures.
PLSLWD staff will continue monitoring Spring Lake in the spring once conditions allow, since our monitoring program has wrapped up for the season. We have a long way to go to clean up Spring Lake, but it looks like this big first step went well.