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In their element

August 09, 2019 by Jacob Friede


Most visitors view the Northwoods and it’s plethora of pristine lakes as the ideal setting for a temporary life of leisure. For the researchers at Trout Lake Station, it’s anything but.

Trout Lake Station is a University of Wisconsin (UW) field research facility on the south shore of Trout Lake in Vilas County, and when the crew of scientists from the UW’s Center for Limnology hit the lakes, they enter a laboratory.

As limnologists, they study inland waters, and since Wisconsin’s Northwoods possesses one of the highest concentrations of inland lakes in the world, they are right at home when they visit. 

Last week an open house was held at Trout Lake Station and scientists were on hand to talk about their research. Here’s a brief glimpse of some of what was going on there this summer.



2,4-D 

Graduate student Amber White is studying what happens to the chemical 2,4-D once it enters a lake system.  The herbicide is often used to combat eurasian water milfoil, an aquatic invasive species.

“I’m specifically interested in where does the chemical go and what happens to it after it’s added to the lake,” White said. “Is it breaking down and how is it breaking down. So I’m looking at how does the sun break it down.”

She’s also trying to find out if the concentration of the chemical stays consistent across the entire lake and if it leaves the lake through inlets and outlets, and she tracks it through the different depth layers of the lake and samples the sediment to see if it settles there. 

“We don’t have results yet,” White said. “I’m still doing monitoring on a lot of the lakes because they had late May or early June treatments, but I’m looking forward to having results hopefully by the winter to know what’s happening.”



Ground water

Undergraduate researcher Mike Krellwitz, under the direction of PhD student Dom Ciruzzi, is involved in a study measuring ground water and lake water levels — through trees.

“We can take cores from trees near lakes and use some models and relationships that we developed to estimate the lake levels for however old the tree is,” Krellwitz said.   

“What we see is that there’s a close relationship between tree growth and the ground water level and then in these really sandy soils water moves very freely so the water level of the lake and the water level of the ground water move at the same elevation. So we go from the tree growth, to the ground water, which we say is the same as the lake level.”

If the ground water level is too low, below three meters, trees can’t access it and will grow less during that period. However, when a tree does have access to the ground water, it grows up to two times larger in a year.    

Those years can be detected by large gaps between the tree rings and thereby give an indication of where the ground water, and also lake water level, was at that particular time.

“It gives us a prediction of ground water level,” Krellwitz said. “But they’re just predictions. Growing season. Disease. There’s a lot of other things impacting the growth of a tree, but we see that water is really the driving force.”



Bass/walleye relationship

Associate research specialist Aly Andersen, along with undergraduate researchers Matt Chotlos and Levi Feucht, have been studying the relationship between bass and walleye.

Natural reproduction for walleye has been on the decline for years up north and they are looking to see if that is due to predation by or competition with bass and other members of the centrarchid, or sunfish family of fish.

“We don’t really understand why walleye are declining so we’re just looking at different possibilities and one of the thoughts is maybe panfish and bass are competing with walleye,” Chotlos said. 

To test this theory they have been removing all the bass and other sunfish from McDermott Lake, a lake in Iron County which used to have a good walleye population, but is now down to about 40 adults.

After two years of bass and sunfish removal, they have one more to go and then they will monitor the walleye population to see if it recovers in any way.

“The one thing that we can change is the competition that they’re having, so we’re removing the centrarchids to try to give the walleye more of an outlet for them to bounce back so they have more resources,” Feucht said.

The diets of hundreds of those captured bass and sunfish have been analyzed by the team but no concrete evidence of predation has been found.

“We checked the diets of a few hundred of them and we haven’t seen that they’re actually eating on the walleye or not,” Andersen said. “Mainly just finding that they’re eating zooplankton or bugs or crayfish.

However, Feucht noted that even if partially digested flesh and bones are found in a sunfish or bass, it is difficult to determine what specific type of fish was eaten.

“We can tell that it is a fish but not necessarily what kind of fish it is,” she said. “So that’s where it gets kind of difficult.”



Coarse, woody habitat

Graduate student Quinn Smith is studying fish response to the addition of coarse, woody habitat on Sanford Lake in Vilas County. Trees were dropped into the northern part of the lake and using radio telemetry he is tracking fish to see if and how they react.

“We are monitoring not only the fish, their movement throughout the system, the preferred habitat and their home range, but also their exchange rates between different portions of the lake,” Smith said.

Smith is tracking nine smallmouth bass, eight walleye, and four muskies.

To track them he inserted radio telemetry tags, which look like a AAA battery, into the fish. A small antennae then hangs out of the fish and is picked up by a receiver when Smith is out on the lake. By following the increased volume of the signal he knows when he is exactly over the fish and then marks the GPS coordinates. He does this twice a week all season and therefore can map out the movements of each fish.

The tags, which do not harm the fish, were first inserted in 2017 and they have a battery life of about 2-3 years and are constantly broadcasting.

“Over time we can figure out, are they more likely to move from the near shore habitat that has wood, to the off shore area, or to the near shoreline that does not have wood,” Smith said. “On a kind of broader scale we can figure out how their home ranges change as the study continues.”



Zooplankton under moonlight

Gretchen Gerrish is Trout Lake Station’s new director, who started June 1. She is a former professor of biology at UW-La Crosse where she was also a member of the River Studies Center, a large research group that works on the Mississippi River.

She arrived this year when the students did and like them, she jumped right into a study.

“Specifically I work on invertebrates, so insects in the water or a group called zooplankton which are microscopic little bugs that live in the water,” Gerrish said. “Right now I’m looking at how light impacts their behaviors. So these guys go down in the water column during the day to avoid fish predation and they come up to feed on the algae at the surface at night and we’re looking at how the moonlight impacts their distribution in the water column.”

Trout Lake Station is home to some exciting and cutting edge work, but don’t tell the researchers they’re working because from the enthusiasm with which the limnologists all spoke of their studies, it was clear they were simply doing what they love. And though they may be visiting, that sort of passion for the lakes is another reason they’re right at home in the Northwoods.

For more information about these and other studies happening at Trout Lake Station visit limnology.wisc.edu.

Jacob Friede may be reached at [email protected] or [email protected]

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