By Dan Gunderson

MPR News/90.1 FM

The Red River has more big fluctuations in water level, more sediment that blocks sunlight and more phosphorus to feed big algal blooms downstream. And in a report evaluating the health of major rivers across the state, the Minnesota Pollution Control Agency has identified farmland drainage as a key factor in the Red River’s worsening pollution.

MPCA regional manager Jim Ziegler said the analysis found that “flash flows” are increasing because of more intense rainfall and very efficient farmland drainage.

The result: A surge of water after a rainfall bringing a heavy load of sediment and phosphorus into the river. They’re often followed by low flows that limit oxygen in the water, making it difficult for aquatic life to survive, especially in tributaries.

Fish and other aquatic life are doing reasonably well in the Red River, but Ziegler said aquatic life declines by 40 percent between the headwaters of the Red River in Breckenridge and the Canadian border, an indication pollution is having a detrimental effect. More people are using the river for recreation, and the catfish population is a strong draw for anglers.

But the farm drainage — with its high levels of phosphorus from fertilizer — is causing significant algal blooms downstream in Lake Winnipeg.

“That’s something that we really need to take a close look at. Some of the data indicate that about 60 percent of the phosphorus that goes into Lake Winnipeg comes from the Red River, so that’s a pretty serious issue, I think, for us,” said Ziegler.

The MPCA report said climate change is causing more intense rainfall, but river flow rates have increased five times faster than precipitation. A big reason: The Red River basin is an area that relies on artificial drainage more than any other place in the world.

A vast network of drainage ditches has been in place for many decades, but there’s been a significant increase in underground tile drainage on farmland in the past few years. Ziegler said state officials don’t know enough about the extent of the tile drainage to understand how the expanded use might impact the river.

The report says that key to addressing river pollution is storing more water in wetlands and improving soil health in farm fields, which would slow the surge of water and pollutants from farm fields after a rain.

“The soil with more carbon content stores an incredible amount of water compared to the soil with lower carbon content, and so just simply improving soil health will reduce those high flows off the land,” said Ziegler.

A number of water storage projects are underway across the Red River Valley, but Ziegler said more will need to be done to offset the growing impact of big fluctuations in river levels caused by flash runoff from fields.