Video: How the 'big brown spot' pollutes the Mississippi River

If we want to clean up the Mississippi River, we have to talk about the "big brown spot."

The big brown spot is the predominant source of pollution to Minnesota's groundwater and river systems. It’s a major cause of decline in habitat, soil health and pollinator populations throughout the Midwest.

And it is the biggest obstacle we face to achieving a clean, healthy Mississippi River.

What is the 'big brown spot'?

The big brown spot is, at its simplest, bare soil. And there's a lot more of it than most people realize.

Minnesota has about 21 million acres of cropland. Most of those acres are used for crops such as corn and soybeans. These "summer annual" crops are planted in late spring and harvested in the fall, meaning they're in the ground for about four months.

The rest of the time, many millions of those acres are bare and empty, devoid of living plants and vegetation. This happens every year, lasting from late fall until planting season in spring — a period of about eight months when rain and snowmelt can be heavy.

This recurring expanse of bare soil is the big brown spot.

Why the big brown spot is a problem for the river

While these fields sit empty, there are no living plants in the ground to stop soil and agricultural chemicals from washing off into our lakes and streams. Nor are there living roots to prevent excess fertilizer from seeping into our groundwater. 

This cropland runoff is by far the largest source of pollution to the Mississippi River (a finding FMR detailed in our most recent State of the River Report), and a root cause of unsafe nitrate levels in drinking water wells throughout the state. It's also one of the main contributors to the dead zone, more than 2,000 miles away in the Gulf of Mexico.

And as climate change continues, more intense rain and snow events will only make these problems worse.

How clean-water crops can cover the big brown spot

The best way to address the big brown spot and stop the regular flow of pollutants into our waters is to blanket the big brown spot with green. We can achieve this with what we call "clean-water crops."

Clean-water crops provide continuous living cover for the landscape. This means they either remain in the ground through all four seasons, over multiple years ("perennial" crops); or they are planted in the fall, stay in the soil through the winter, and are harvested in the spring ("winter annuals"). Importantly, there are commercial markets for these crops. Growers will be able to harvest and sell them, creating new economic opportunities and revenue streams from land they already work.

Examples of clean-water crops specially bred for our climate include:

  • Kernza perennial grain
  • Winter camelina
  • Pennycress
  • Hybrid hazelnuts
  • Winter barley
  • Elderberry
  • And more

By integrating these crops into our existing, established farm practices, there will be live plants on the ground and deep roots in the soil all the time, not just during the summer months — covering the big brown spot in green vegetation, providing new revenue streams for farmers and significantly cutting how much agricultural pollution reaches Minnesota's waters.

Help us get to continuous living cover

The power of clean-water crops to help heal the river is why FMR is working to make these crops a reality on the landscape. Getting there requires a collective effort: from the researchers and experts at the U of M's Forever Green Initiative, to the farmers taking early, supported risks; to the businesses that turn these crops into delicious eats or next-gen biofuels, to the consumers that vote with their wallets

FMR and our River Guardian advocates champion these researchers, farmers and businesses each year at the state Legislature — and, increasingly, at the federal level — yielding crucial investments in the advancement of continuous living cover. Make a difference by signing up to be a River Guardian so you can help advocate for the policies we need to make this vision a reality.

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