Data from 24 lakes across state measure evolving eco-systems.
A species of cold-loving fish has died in large numbers in northern Minnesota lakes this summer -- putting it at the center of a study looking at the effects of a warming climate on the state's lakes.
Tulibee -- a key food fish that thrives in cold water -- have died in batches before in warm summer weather, said Peter Jacobson, fisheries research supervisor with the Minnesota Department of Natural Resources (DNR). But the die-offs have been occurring more frequently in recent years, Jacobson said. Figuring out why will be part of a detailed look at what's been happening in Minnesota lakes, and how the lakes might respond in the future to warmer summers and shorter, thinner-ice winters.
The Sentinel Lakes project, funded by an $825,000 grant from the Legislative Citizens Commission on Minnesota Resources and involving the DNR and the Minnesota Pollution Control Agency (MPCA), is looking at the effects of a warmer climate on the relationships among fish, aquatic plants and invasive species as well as at water chemistry and quality in 24 lakes across the state.
The project also will look at effects of residential development, agriculture, aquatic plant removal and such invasive species as Eurasian water milfoil and curly leaf pondweed. Results, along with ongoing monitoring, could help officials change how they manage lakes as the climate warms.
Four ecological zones
The 24 lakes being studied are sprinkled across four distinct ecological zones, from the cold, deep lakes of the Arrowhead to the shallow, soupier lakes of southern Minnesota. The aim is to collect extensive information on lakes that are representative of the state's more than 15,000 lakes.
"We have a little bit of information on a lot of lakes," said Steve Heiskary, an MPCA research scientist who is also working on the study. But Heiskary said that only the state's marquee lakes -- Mille Lacs, Minnetonka, Vermilion and a few others -- have ever been studied in great detail, yielding information that might not be applicable to other lakes.
In most Minnesota lakes, for example, little is known about water temperatures at varying depths and over time. Anglers and fishing guides might test for those, but not in any consistent way. Probes in the Sentinel project's lakes have been measuring water temperatures every 30 minutes.
The study is in its third year, and the DNR and the MPCA will be seeking funding for another three years during the 2013 legislative session.
Tulibee, also known as cisco, are an important food source for some of Minnesota's iconic and trophy fish such as walleye, northern pike and muskie, Jacobson said. Monitoring so far has found not only some declines in the tulibee population over several years on some lakes, but a simultaneous increase in panfish more suited to warmer water, such as bass and sunfish.
Meanwhile, research has also shown an apparent relationship between winter conditions and curly leaf pondweed, a Minnesota resident plant for more than a century but still regarded as an exotic invasive. Snowy winters, which limit sunlight penetration through ice, inhibit its winter growth, but winters like that of 2011-12, with little snow and early ice-out, trigger explosive growth, Heiskary said. Warmer winters could either resemble last winter, or be very snowy, as the winter before last was.
"Climate warming leads to higher variability," Heiskary said.
The Sentinel Lakes project is also measuring pesticides and nutrients in participating lakes. In addition, researchers will track the effects of zebra mussels, a more recent invader, in Lake Carlos near Alexandria, in hopes of predicting what might happen as it spreads to other lakes.
Bill McAuliffe • 612-673-7646