Painting a more complete picture of water quality in one Minnesota lake
Ann Lake, located in Kanabec County in east central Minnesota, is one of several problem lakes in the state due to excess nutrients and high algae abundance.
In 2022, the Minnesota Pollution Control Agency (MPCA) called upon the scientists at the Science Museum’s St. Croix Watershed Research Station (SCWRS) to conduct research on the lake to better understand its current condition in the context of its history. Was it always nutrient-rich? Has it been worse in the past? Is it improving? And what does the future hold for Ann Lake?
Sediment cores tell the story of a lake’s history
For their Ann Lake study, SCWRS staff conducted sediment coring, a sampling method that allows them to go get a more detailed picture of the lake's history.
Every year at the bottom of a lake, a new layer of muddy sediment forms on top of the old layers. This creates a record of everything that’s ever drifted to the bottom of the lake — including fish, algae, and even pollen from thousands of years ago. To conduct sediment coring, researchers drive a special tool into the lake bottom to extract a column of this sediment, which they then analyze to get a better picture of the lake’s ecological history.
In addition to sediment coring, SCWRS scientists conducted a study of Ann Lake’s modern nutrient dynamics, using a buoy full of instruments to take readings every 30 minutes. They collected more than 50,000 data points over the course of the summer study.
What did the data tell us?
The combination of the mud and data collected told SCWRS scientists what has happened to Ann Lake and why it is suffering. The lake became more nutrient-rich after Euroamerican settlement, but has gotten markedly worse since the lake was dammed in 1965. That flooding of new land has led to a nutrient-rich brew in the sediments that can cycle into the water column several times a year following the dog days of summer. Those nutrients fuel algae in the water, creating poor water quality in some summers.
Meeting Kanabec County residents
Research Station scientists travel all over the region (and the world!) to study water quality. But just as important as their fieldwork and lab analyses is sharing what they’ve learned. SCWRS staff spent time talking with area residents and regulatory agencies about their research and what it revealed about the condition of the lake.
The MPCA captured footage of that season-long research and outreach, which it shared at a stakeholder presentation earlier this summer in Ogilvie, Minnesota. See Science Museum researchers at work on the water and in the community as they searched for clues about Ann Lake’s past, present, and future.
