Jim Leverance turns the key in the ignition. The engine grumbles. He backs the boat away from the Olin Park launch and points it south toward Turville Bay. It is a few minutes past 8 on a Tuesday morning. The sky is the pale blue tone of a day still getting under way, yet the climbing sun is already radiating heat off the surface of Lake Monona.
A retired team leader for Wisconsin Department of Natural Resources water programs in the lower Rock River basin, Leverance now works part-time as an aquatic plants specialist for Dane County's Office of Lakes and Watersheds. Steering the boat past Turville Point at a slow/no-wake speed, he launches into an explanation of what's going on in the far southwest corner of Lake Monona.
A five-year science experiment. This may be the simplest way to put it. In collaboration with the DNR and the Army Corps of Engineers, the county is investigating strategies for controlling invasive Eurasian watermilfoil. But the full explanation is as complex as the problem itself.
Since its first appearance in the Yahara chain of lakes circa the 1960s, Leverance says, Eurasian watermilfoil has thrived at the expense of native species. "The problem is that it gets so dense and grows so early that it forms a canopy on top of the water, which shades out the native plants - the ones that we'd like to have here. It's a competitive disadvantage for the native plants."
Not to mention a nuisance for swimmers and boaters. Twice during this morning foray, Leverance will throw the engine into reverse to untangle the propeller. "Recreation becomes very difficult," he continues. "Watermilfoil often facilitates filamentous algae, that stringy hairlike algae growth on top of it. And when you've got birds walking around on it, it isn't very conducive."
Eurasian watermilfoil can also hurt fisheries, Leverance adds, because it can grow "so thick and so dense that it makes it very difficult for the large fish to eat the little fish. So you end up in some lakes with a lot of little fish. They get in the vegetation, they hide out, but the big fish can't get at them. You end up with stunted panfish and poor growth in your gamefish."
The density of Eurasian watermilfoil also can stall the movement of water through the lower Yahara lakes. "Particularly in the area below Lake Waubesa down to Lake Kegonsa, there is not a lot of gradient in that stream," Leverance observes.
Mechanical harvesting has been the traditional method of mitigating these problems, but research into alternative strategies is ongoing.
The first three years of the five-year study will involve what Leverance calls "active management" early in the season, when Eurasian watermilfoil starts to grow but before native plants flourish.
"We have seven five-acre parcels," Leverance says. Three will serve as reference sites and remain undisturbed throughout the study. Two will be harvested early in the season in an effort to open up the Eurasian watermilfoil canopy for native species. Two more will be treated early in the year with small concentrations of 2,4-D, an herbicide Leverance describes as "very selective toward the type of plant that Eurasian watermilfoil is."
Leverance says aspects of the Turville Bay project were precipitated by a study at Fish Lake that "looked at harvesting with aquatic plant cutters that could cut deep, and see if you could cut Eurasian watermilfoil at the sediment's surface to create, basically, fish highways. The fish highways would facilitate the gamefish to cruise up and down."
The results were "heartening," Leverance says. "They found increased growth of both the panfish population and largemouth bass, the primary predator. And they also saw that with cutting deep on the Eurasian watermilfoil, they had control for about two to three years.
In aerial flights, they could see remnants of the channels that they had cut through the vegetation. "So that was one reason we looked at deep harvesting as part of the Turville Bay project in conjunction with the 2,4-D treatment."
The last two years of the five-year Turville Bay project will involve continued monitoring of plant communities in the seven five-acre parcels.
If the results at Turville Bay prove favorable, they may hold lessons applicable to what Leverance calls "the continual parade of aquatic invasive species that come into the state. The easiest way to deal with new aquatic invasive species," he says, "is generally to get a handle on them right away before they get to be to the point that they have in the Madison lakes, where they're very thick and very problematic."
