DNR Drawdowns Let the Sunshine In - from Fist & Wildlife Today, Spring 1998
Biologists replicate drought conditions to improve the ecological health of two shallow southern Minnesota lakes.
NOTE: WE ARE REPRINTING THIS ARTICLE AS A POSSIBLE MODEL SOLUTION FOR THE WHEELER-SCHULTZ-HUBBARD CHAIN OF LAKES NUTRIENT LOADING PROBLEM.
It's been nearly a decade since southern Minnesota had a decent drought, the kind tat drops water levels in large lakes enough to expose the seeds of water plants to sunlight so they can germinate.
Because aquatic plants are essential for keeping shallow lakes clear and able to support healthy wildlife or game fish populations, the DNR is doing on two large lakes what nature isn't; lowering the levels.
Swan Lake in Nicollet County is one of the state's premier waterfowl waters. But according to Dennis Simon, wildlife manager at Nicollet, the lake desperately needs a temporary drawdown to re-establish emergent vegetation (primarily bulrushes and cattails) it has lost during the past several years. The plants provide wildlife habitat and absorb waves, which otherwise stir up bottom sediment that block sunlight from reaching underwater vegetation. Lake plants also deplete the supply of nutrients in the water that can fuel algae infestations. And emergent plants such as bulrushes reduce shoreline erosion by absorbing waves.
"The combination of high water and exploding muskrat populations over the past several years decimate the emergent vegetation at Swan Lake," says Simon.
In addition to the foot of water the DNR drew off Swan Lake last fall, another foot will be dropped during the spring and summer of 1998. The DNR agreed to the drawdown after meeting with hunters and other lake users last fall.
"We're hoping the drawdown will help thicken some cattails and bulrush stands out in the lake that right now are very thing," says Simon, who adds that eventually, the lake will have to undergo a more severe drought or drawdown to significantly increase the amount of emergent vegetation. "But for now, we'll see what we can accomplish with this 2-foot drawdown".
In March, the DNR also began lowering the water level of Lake Hanska in Brown County. The 2.5 foot drawdown, part of an effort to improve water clarity, complements a lake level reduction of 1 foot this past winter. Stop logs now removed from the water outlet structure will be replaced in July so the lake can return to normal level.
This is the first time the DNR has tried lowering water in winter and spring, says Don Schultz, area wildlife, manager at Redwood Falls. "Previous temporary drawdowns in spring and early summer were largely unsuccessful because water levels could not be lowered quickly enough to allow time for plants to grow before we had to raise the level again," Schultz says. "We're hoping that this year we got a jump on things early enough for plants to get a foothold".
Schultz says Lake Hanska currently has virtually no aquatic plants. "The lack of vegetation is a key reason for the continual decline in water quality," he says.
To prevent the 1,844 acre from degrading further, Schultz has been working with Hugh Valiant, fisheries supervisor at Waterville, and local citizens on a plan to expose some lake bottom to promote plant growth in the exposed areas.
Drawdowns should expose roughly 500 acres of lake bottom, Schultz says. In addition to keeping the water cleaner, the plants will provide habitat for waterfowl, fish and other aquatic animals. Additionally, the process will tell biologists about how well the Hanska water control structure works to lower water levels.
Valiant says the lake currently has a fair walleye population but numerous carp and balk bullheads are crippling a lake ecosystem already struggling from a continual influx of pollutants from farm fields and roads. "The current partial drawdown will help improve water quality, but it's not a long-term solution, Valiant says.
Sometime during the next few years, he explains, the lake will need to be lowered even further and then treated with a chemical called rotenone to kill the entire fish population. (Editor's note: See "Making the clean kill," pages 4-5). Valiant says the DNR would then stock the lake with game fish, as it did following the Lake Hanska reclamation in the late 1980's. The rough fish kill and subsequent stocking produced excellent game fish populations during the early 1990's. Anglers throughout the region were catching large numbers of 3 and 4 pound walleyes.
In recent years, carp have returned to the lake, requiring another reclamation.
Thought Valiant said lake reclamations and drawdowns can be "powerful tools" for improving fishing. They are definitely not cure-alls. "Unless major changes are made in land use practices within the watershed of a reclaimed or lowered lake, the lake and its fishery will eventually revert back to the state they were previously in," he says. "That's what's happening at Hanska".
Valiant, Schultz, and others working to restore Hanska believe it can eventually become a superb fishing, swimming, and wildlife lake, but only if citizens team up with private and public conservation groups to get at the root of the lake's water quality problems.
And that, says Valiant, means permanently reducing nonpoint-source pollutants flowing in from the countryside and nearby towns, bot just lowering water levels not and then.