The Environmental Science class at St. Mary’s High School conducted an aquatic vegetation survey on Sleepy Eye Lake on May 16 and 17.
The Environmental Science class at St. Mary’s High School conducted an aquatic vegetation survey on Sleepy Eye Lake on May 16 and 17. Their teacher, Mary Beth Botz, explained that the purpose of the activity was to involve students in a real world learning experience, to see firsthand the prevalence of the invasive species—curly pond weed, to add to the vegetation data being collected by the DNR and to educate the public by sharing the survey results, thus the lake map included here.
Botz and the class consulted with Allison Gamble, MN DNR Invasive Species Specialist, as they planned the survey activity. The students were ferried around the lake to collect plant species by Wayne and Patti Pelzel on May 16 and by Mike Schauman and his nephew on May 17.
Students sampled 91 designated GPS points. The coordinates were established and used by the DNR for their baseline survey conducted in the summer of 2015. At each sampling site, one student noted the location on the lake map, one cast and pulled in a double sided rake, one student identified the plant species snagged by the rake and one student tallied the species found and how many individual plants of each type were found at that spot.
Botz said that City Manager Mark Kober explained that for the three prior years (2013, 2014 and 2015) beach and other high use areas [designated in red on the lake map] were treated with a granular herbicide to target the invasive species, curly pondweed. Kober said no treatment was done in 2016, but the city will treat again in 2017.
Curly pond weed is an early emerging aquatic plant; therefore, the granules are applied into the lake when the water temperature is between 53 to 60 degrees F, which is usually at the end of April. Permits to treat the lake must be obtained from the DNR. The city then hires a contractor to spread the granules. As an early emerging plant, curly pondweed chokes, or hampers, the growth of the native plants.
“Native plants are necessary to the lake,” said Botz. “People often refer to all the plants in the lake as weeds, but they actually are important to the lake ecology.” The functions supplied by native aquatic vegetation include: 1) Photosynthesis, pulling out carbon dioxide and putting in oxygen. 2) Binding up phosphates and nitrates (there are more phosphates in our lake, some occuring naturally in the soil and some due to run off). 3) Provide habitat for the small invertebrates at the bottom of the food chain.
Botz shared an interesting fact. “Sometimes the lake water has a distinctive musky or musty smell,” she said. “This odor is caused by chara, which is also called muskgrass or skunkweed. Chara is native and is actually a gray-green branched multicellular algae that is often confused with submerged flowering plants.”
Remarking on the vegetation survey map, with only a few spots of water lilies marked, Botz said, “Those who fish or boat in the west end of the lake would probably contest the meager results for white water lilies because the lily leaves and flowers now form a thick mat seemingly covering the entire surface of the lake.” She said they have to remember that the survey was done in mid-May, before the lilies grew and spread to the point they are today.