A look at why lakes are green

By Jason Schoonover, special to the Tribune

Published Tuesday, September 2, 2008

The Shell Rock River Watershed District board has come out with a list of prioritized plans to improve water quality and algae levels in the lakes and waters of Freeborn County, a process leading to the dredging of Albert Lea Lake and Fountain Lake.

Clayton Petersen, a board member of the Shell Rock Watershed District board and an agronomist, said he sought to be on the watershed board because he comes from a background based in science and feels he can use this knowledge to help the watershed board.

A major step by the watershed board has been to make a list of their projects through 2015 available to the public. The board compiled all issues, prioritized them and put a dollar amount to each issue to show how it will be taken out of the sales tax each year. This gives the public a plan as to when each project will be dealt with and where the money is going.

“That allows us to know how many projects a year we’re going to get done and which ones,” Petersen said. “Everybody has a date of when the project will get done. They have the cost — what it’s going to cost to do it. Everything is open. What this does is give us a strategic plan.”

Petersen said one of the biggest challenges they’ll face is how to adjust the projects to the fact that the sales tax comes in increments from year to year. While he said Fountain Lake could be dredged in one year, they wouldn’t be able to pay for it in one year.

The watershed board is working with the county and other local agencies to advance the project list to 2012 or 13 when Fountain Lake will be dredged. Albert Lea Lake will be dredged a few years after that. But before that can happen, Petersen and the watershed board are working with the county and other local agencies to correct issues upstream and in the city, such as installing rock dams to slow the velocity of the water, so that when the lake is finally dredged, it will hopefully not fill back in.

“If we’re going to dredge, take what’s in the lake, you need to not let it fill back in,” Petersen said. “Fountain Lake has been dredged three times. It fills back in and we’re back to where we are. We don’t want to have that happen again.”

According to Petersen, the biggest factor affecting water quality and causing algae to form in the lakes may be how the lakes were formed. After the glaciers receded to form the lakes of Minnesota, some believe southern Minnesota’s lakes filled back in with some sediment, making them shallower than the lakes of northern Minnesota.

Shallower lakes are more prone to see a mixture of the two things that cause algae in lakes: phosphate and nitrogen. While phosphates are not soluble and sink to collect on the bottom, nitrogen reaches the water naturally through things like thunderstorms. Nitrogen is soluble in water so it mixes throughout the water. Nitrogen and phosphate mix when the phosphate is stirred up and mixes with the water, this is usually done by boats. Since the lakes of southern Minnesota are naturally shallow and have a buildup of phosphates at the bottom, Petersen said there are two solutions to this issue: deepen the lakes through dredging or stop boating on the lakes.

A common belief is the phosphates in the lakes often come from fertilizers used on farms. Petersen said this is not the case because these phosphates bind with the soil and can only move through soil erosion.

According to Petersen, the only way field soil can reach lakes is through soil erosion, and there are already safeguards in place to ensure that rarely happens. Petersen said Freeborn County has one of the highest sign up rates in the county for ditch-bank erosion control, a Natural Resource Conservation Service program where farmers are paid to leave about 30 feet of grass between a field and a body of water so eroding particles are captured by the grasses.

“What happens then is any sediment will hit that grass and won’t get to the lake,” Petersen said. “The banks are usually the part that washes out so now those are pretty well-stabilized. In Freeborn county, most of their ditch banks and things have some type of grass barrier around them. That type of pollution has been pretty much taken care of in Freeborn County.”

Along with those ditch banks, the county is working to make the slopes along waters less steep, to further thwart the chances of erosion.

Another major source of phosphate in the lakes is animal waste, particularly from geese and ducks. Petersen said seven geese in a week’s time produce about two pounds of phosphate. Take that in account with the number of ducks and geese on the lakes over a number of years and other sources of phosphate, Petersen said that every lake in Minnesota has about two feet of phosphate that sinks to the bottom, but differences in the depth of lakes affect how easily the phosphate can be stirred up.

“Why (is it) in southern Minnesota they have algae and in northern Minnesota they don’t have any?” Petersen said. “If you have an eight-foot depth and you have a motorboat go across it, it will stir up as much phosphate as you need for algae to form. In northern Minnesota, their lakes are 40 feet deep. There’s probably two feet of phosphate at the bottom of their lakes too but it never gets stirs up so it doesn’t mix with the nitrogen.”

Geese and ducks are not the only source of phosphates in the lakes, trees take nutrients out of the ditch banks and leaves then fall or blow into the lakes. So phosphates will naturally enter the lakes; however, Petersen said even if no new phosphates could enter the lakes, there would still be enough to affect the lakes for years.

“Once you fix the ditch banks and the soils erosion, after that it’s nature. You can’t really stop some of it. You’re not going to kill all the geese. You’re not going to kill all the trees,” Petersen said. “You’ve got two feet (of phosphates) in the bottom of your lakes. Albert Lea (Lake) is shallow, so every year it doesn’t matter what comes into the lakes, we’ve got more than enough for a million years to stir up. So we could have zero coming in and we’d still have the problem. The biggest point source contamination is in the lake. It’s at the bottom sitting there.”

Like Petersen said, the only way to correct this problem is through dredging the lakes to remove the materials at the bottom of the lake. Before the lake can be dredged, certain steps have to be taken. Petersen said sonar testing will determine the original bottom of the lake to set how deep dredging is allowed to go. Core samples are also taken to determine what is on the bottom. Petersen said these steps are already underway. Even the material removed from dredging can be beneficial. It is removed from the lake and taken to a field, as long as it does not contain heavy metal or other pollutants and works as a fertilizer.

The Department of Natural Resources has already classified both Fountain Lake and Albert Lea Lake as recreational lakes, so this allows certain things to happen that could not happen to a wildlife lake.

“With Fountain Lake being strictly recreational, you’d like to dredge the depth to 15 ft. deep and 20 would be better but this is dictated by the sonar readings,” Petersen said. “Normal motor boats won’t stir up the bottom of the lake at the 8- to 10-foot range. Twelve is usually what they aim for.”

A misconception Petersen mentioned is that shallow lakes to attract ducks. He said this is not true, because deeper lakes in northern Minnesota have ducks. In fact, Petersen said lakes with varying structures are preferable to keep the shallower areas from filling in.

“Like Albert Lea Lake, if you dredged the west basin, basically west of the freeway, the east side wouldn’t fill back in the west side because it moves to the east,” Petersen said. “You can have all types of environment. The best lakes are the kind that have both. They have some shallow and some depth. It creates ideal situation for fish. It creates ideal situation for geese, ducks.”

While there have been misperceptions about the issues concerning the lakes, Petersen said the steps that have been taken are not necessarily widely known in the community, but Petersen said he is ok with that as long as the problem is fixded.

“It’s like the ditch banks with a 30- to 60-foot buffer,” Petersen said. “No one really knows about them. They’re not flashy. Nobody knows Freeborn County has one of the highest sign ups in the nation concerning this. It’s not flashy. We fixed the ditch bank north of Interstate 90. The watershed and county worked together there. How many people know we did it? It’s not in your face. Dredging, when the machine’s out there, people are going to go, ‘Wow! There’s something going on.’ What the people ask us to do is take care of the problem long term. I don’t care if it’s flashy or not. Here’s the process we need to do. Here’s what has to get done to get it done right for future generations. That’s really the concern.”