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Cleaning Up Lake Pepin

by Dean Rebuffoni

The year was 1988, and Lake Pepin — one the biggest, most scenic, and most popular waters in the Upper Midwest — was a smelly mess.

The Mississippi River flows through the 25,000-acre lake, and a prolonged summer drought had greatly reduced the flow, dropping water levels in Pepin. The result, a Metropolitan Council report stated, was "severe nuisance algal blooms [that] caused unsightly surface scum, obnoxious odors, low oxygen levels, and localized fish kills" in the lake.

It also caused a loud outcry. Do something, the public said, to prevent a recurrence of the mess of 1988.

Several major efforts have since been launched to help do that, including studies of the lake and projects to reduce the volume of algae-promoting nutrients — most notably phosphorus — discharged into the Mississippi from sewage-treatment plants upstream of Pepin.

Pepin continues to suffer from high levels of nutrients, however, and a new effort is underway to improve the lake's lot. It is officially an "impaired" water, and the federal Clean Water Act requires states to evaluate such waters to determine the sources of pollution and reduce the harm.

The effort is a bureaucratic mouthful: the Lake Pepin Watershed Total Maximum Daily Load Project for Eutrophication and Turbidity Impairments. Informally, its the Lake Pepin TMDL. The North Star Chapter of the Sierra Club is among three dozen private and public stakeholder organizations advising the new effort.

A TMDL is an estimate of the largest amount of a pollutant that a waterbody can assimilate without violating water-quality standards. That includes pollutants from point sources — the end of a sewage-discharge pipe, for example — and nonpoint sources such as the tainted runoff from farm fields and city streets.

Although the effort focuses on Pepin, it includes the 60 miles of the Mississippi between Pepin and the Minnesota River, a stretch of the Minnesota, and Spring Lake, an 1,800-acre river backwater at Hastings.

However, improving water quality in Pepin will require corrective action at sites throughout a huge watershed that drains into the lake. That means the drainage basin of the Mississippi upstream from Pepin, the entire basin of the Minnesota and St. Croix rivers, and several lesser streams that flow directly into Pepin.

All told, the lakes watershed covers more than half of Minnesota and a big chunk of northwestern Wisconsin. The TMDL effort will study a lot of territory before actual on-the-ground work is begun.

"We have a four-year timeframe," said the project's coordinator, Norman Senjem of the Minnesota Pollution Control Agency. "That's how long we have to complete the study and to determine pollution-load allocations for point and non-point sources of [algae-promoting nutrients] as well as sediment."

Although Pepin is shared by Minnesota and Wisconsin, most of its nutrient and sediment problems originate in the former. Some scientists estimate that 80 to 90 percent of the sediment entering the lake comes from the Minnesota River's heavily farmed watershed.

As Senjem put it, "a plume of sediment extends from the Minnesota into Lake Pepin," which acts as a sink for much of the sediment and for phosphorus that is naturally fixed to the sediment. That's bad news for the lake but, without Pepin, those materials would be carried much further down the Mississippi.

A key component of the TMDL study is an advisory panel of 18 scientists from state and local governments and colleges in Minnesota and Wisconsin. They include experts in soil science, erosion processes, nutrient cycling, aquatic life, drainage and lake monitoring.

While the TMDL process is directed at reducing the influx of phosphorus and another nutrient, chlorophyll-A, sedimentation poses a more serious threat to Pepin's long-term health.

According to a study by the St. Croix Watershed Research Station, part of the Science Museum of Minnesota, Pepin is filling with sediment at 10 times its natural rate, and will be completely filled within 340 years. The upper end of the 22-mile-long lake is expected to be filled in about 100 years.

By "natural" rate, researchers mean the rate before European settlers arrived in large numbers in the early 1800s. They also estimate that phosphorus is accumulating in the sediment on the lake's bottom at 15 times the natural rate.

The most dramatic increases in both sediment and phosphorus loading began in the 1940s. Those increases are related to, among other causes, increases in the planting and fertilizing of row crops, largely corn and soybeans, particularly in the Minnesota Rivers drainage basin. Land planted in row crops is more vulnerable to erosion from storm runoff and snowmelt that, in turn, carry the sediment into streams.

"We need to take steps to extend the life of Lake Pepin," said Gary Wege, who represents the U.S. Fish and Wildlife Service on the stakeholder advisory committee. "That means we need to decrease the loading of sediment to Lake Pepin."

Another committee member, Kris Sigford of the Minnesota Center for Environmental Advocacy, put it this way: "Ultimately, the goal of the TMDL is to prevent Lake Pepin from being covered with algae and dead fish. We need to reduce the volume of phosphorus thats being carried into Pepin in sediment and, simultaneously, reduce sedimentation of the lake."

She also wants to accelerate the overall TMDL effort. "I want clean water in my lifetime," said Sigford, who is 51.

More information about Lake Pepin and the TMDL study can be found at these Web sites:

Dean Rebuffoni can be reached at drebuffoni@mn.rr.com or (612) 920-9632.