One of the biggest threats to MN’s water is one you’ve probably never heard of

By Leigh Currie, MCEA Chief Legal Officer

The “Dead Zone” in the Gulf of Mexico. Nitrate-contaminated drinking water. Fish kills. Algal blooms. These are some of the environmental issues you’ve likely heard of, but what do all of these things have in common? An environmental issue you probably haven’t heard of: agricultural drainage. So, what is it, why do we care, and what can we do about it?

What is it?

Maybe you haven’t heard about agricultural drainage, but maybe you’ve heard that Minnesota has “lost” half of our wetlands. In southern Minnesota, the percentage of lost wetlands is more like 80. But to be clear, these wetlands weren’t “lost;” they were drained to increase crop yields. It turns out that some crops, especially corn, don’t like wet roots. 

When Minnesota was first being settled, farms were preferred over “swamps.” Our once-bountiful wetlands were not seen for the benefits that we now know they offer; benefits like filtering pollutants, protecting us from floods, and storing way more carbon than all of the world’s forests combined. Instead, they were seen as mosquito factories limiting otherwise rich, available cropland. So Minnesota passed laws that created pathways to drain the wetlands and plant crops instead. 

These pathways allowed farmers to install “drain tiles” under their fields that would shunt excess water on their fields to ditches –- either human-made ditches or natural streams that could be dredged or straightened to act as a ditch. Initially these drain tiles were made of clay and laid down under fields where they would collect rainwater or groundwater invading root zones and drain it away. We still call them “drain tiles,” but today they are black plastic tubes with perforations designed to allow the water to filter into them and then flow away. In some watersheds, up to 85% of the land may have this hidden network of plastic pipes lurking beneath the surface, sometimes amounting to more miles than the roads above ground. And most of us don’t even know they’re there.  

 A sign warns swimmers to be aware of the risks of blue green algae at popular swimming beach

Lake Nokomis July 24, 2024.

Why do we care?

Increased crop yields are good, right? Well, yes, but we’re doing it in a way that is wreaking unnecessary havoc on our water quality. It’s why we’ve seen algal blooms tank the swimmability of more and more of our lakes; why an increasing number of fish kills are found in our streams; why homes on the banks of the Minnesota River have collapsed; and why more of our drinking water is impaired by nitrates and other contaminants that have been linked to health harms such as blue baby syndrome and cancers. Because here’s what happens when you accelerate the removal of water under farm fields: the soil and microbes in the soil don’t have time to work their magic.      

Soil can be a very effective filter for things like nutrients and pesticides. When you short-circuit that process, those pollutants don’t get filtered out. Instead, they run straight into our streams, rivers, and ultimately to the Gulf of Mexico. This short-circuiting has significantly contributed to excess nutrients in our water (like nitrate), excess sediment in our water, and just excess water itself. 

We’ve been trying to decrease the concentration of nitrate in our water for decades by asking the agricultural industry to change practices. But it’s not working. Nitrate in our water comes almost entirely from fertilizer applied to crops, either in the form of manure or commercial fertilizer. Pretty much every study that looks at the problem points to agricultural drainage systems as a major contributor. That means we can’t fix our nitrate problem, or the havoc it's wreaking both in and outside Minnesota, without dealing with drainage. 

A fish kill in a stream

What can we do about it?

The good news is that it doesn’t have to be this way. There are ways that agriculture can be productive and waters can be protected. The solutions mostly involve slowing the water down. Slowing it down gives the pollutants and sediment in the water time to filter out before the water hits our streams and rivers. You can add storage features to drainage systems that hold the water back, for example, or allow the system to widen out into a floodplain so more manageable quantities of pollutants, sediment, and water hit our streams and rivers at any one time. There are also storage systems with “bioreactors” that help remove nutrients like nitrates before the water filters out. The bioreactors are essentially woodchip-filled underground storage areas where the water makes a pit stop before continuing its journey. 

So why doesn’t every drainage system just add more storage? It’s the usual answer when it comes to placing a value on natural resources: money. It’s cheaper to just trench a straight line from a drain tile outlet to the stream than it is to add a storage pond or a bioreactor. And our drainage laws don’t have a mechanism to account for the damage caused downstream, meaning farmers aren’t incentivized to choose a different option. 

We need drainage authorities—the government bodies - mostly at the county level - in charge of approving drainage projects—to include the cost to our shared public resources in their calculations. The analysis shouldn’t just be “will this ditch allow the farmers to produce more bushels of corn?” but rather, “is this ditch worth it when you balance the additional bushels of corn against the harm it poses to our water?” 

Unfortunately, drainage authorities don’t feel empowered to ask this latter question because of how the law is written. That needs to change. Until it does, we need to continue to subsidize and encourage good drainage features and discourage harmful ones. 

MCEA has been working on agricultural drainage for years and is well aware of this stubborn roadblock. We have some exciting and innovative strategies in the works aimed at finally knocking it down. Stay tuned!