Wetlands quietly clean up pollution - and save communities millions

When people think of wetlands, they usually picture soggy marshes with tall grass, frogs, and maybe a few ducks. What most don’t realize is that these places are doing serious work behind the scenes.

Wetlands help clean our water, support wildlife, and reduce flooding. Now, new research shows they’re also saving local governments a lot of money.

All along the Mississippi River Basin, farms cover the landscape. They grow the food that feeds millions, but there’s a downside.

When it rains, fertilizers from those fields don’t just stay put – they wash into nearby streams and rivers.

That runoff carries nitrogen and other nutrients that throw water systems out of balance. It can trigger algae blooms, harm fish, and even contaminate drinking water.

Wetlands take on pollution – and win

A recent study shows that wetlands across the Mississippi River Basin are doing a solid job cutting down nitrogen pollution.

This is not just important for the environment – but for people, wildlife, and anyone who relies on clean water.

Instead of only trying to stop pollution at the source, the researchers focused on what happens after nitrogen has already made its way into rivers and streams. That’s where wetlands come in.

They act like filters, helping to break down nitrogen and release it into the air as a harmless gas called N₂.

Measuring real results over time

The study was conducted by teams from the University of Illinois Urbana-Champaign and Montana State University. They looked at wetlands created through a federal program that pays landowners to retire farmland and let those areas return to wetland.

Once restored, the land starts working again – just in a different way. From 1990 to 2018, around 9,000 permanent wetland easements were added to the Mississippi River Basin. That’s a small slice of land – just 0.22% of the region – but the effects were noticeable.

After about three years, restored wetlands lowered ammonia levels by 62% and total Kjeldahl nitrogen (TKN) by 37%.

That means a reduction of 0.08 milligrams per liter for ammonia and 0.20 milligrams per liter for TKN. These are big improvements in water that flows through heavily farmed areas.

The results didn’t just come from small studies. The team looked at large-scale data over decades and controlled for weather patterns and seasonal changes.

Wetlands keep working under pressure

Phosphorus, another common pollutant in farm runoff, didn’t show a strong response in the long term. There were some small improvements downstream, but not the same consistent impact seen with nitrogen.

Still, the nitrogen cleanup alone is a win. It’s a major part of the water pollution problem in the U.S., and fixing it isn’t easy.

Some people worry that wetlands might get overwhelmed when there’s too much fertilizer in the water. But this study found the opposite.

“We might be concerned that these wetlands can be overrun by too many nutrients, so they can’t filter them effectively. But we’re finding a large impact in areas with lots of nutrients,” said Nicole Karwowski, agricultural economist at Montana State University.

“Thus, wetlands are not only able to filter average waters in the Mississippi River Basin; they’re very good at doing it in places that have the biggest problems with nutrients.”

Cost savings for cities

All that nitrogen has another side effect – it costs cities money. Drinking water has to meet federal safety standards, so treatment plants work hard to clean it up before it reaches people’s homes.

When nitrogen levels go up, so do the costs to get that water safe to drink.

According to the study, restoring just 100 acres of wetland in a small watershed could save large public water systems up to $17,000 a year in treatment costs. Spread that across the region, and the savings add up fast.

In total, these wetlands could help local governments save as much as $200 million every year. The federal government covers the cost of restoring the wetlands, but it’s the local communities that end up with the financial payoff.

“The wetland easement programs are essentially a cost transfer from the federal government, who is paying for the restoration, to local communities,” noted Marin Skidmore, assistant professor at the University of Illinois Urbana-Champaign.

That’s a rare win-win. Instead of spending more on expensive filtration technology, cities can let nature take care of part of the problem.

Protecting wetlands, fighting pilgrim

Despite the benefits, many wetlands may not be protected much longer.

A recent Supreme Court decision says that only wetlands next to navigable waters – like rivers and streams – fall under the Clean Water Act. In Illinois, this puts 72% of wetlands at risk of being developed.

Losing these wetlands could take away the clean water and cost savings they provide. Researchers are already looking into whether wetlands still help even if they’re not right next to a water source. So far, the answer seems to be yes.

“Hopefully our results can help policymakers make decisions about wetlands and whether they should be protected. Wetlands can work in tandem with other nutrient reduction strategies, such as cover crops, buffer strips, and more efficient nutrient use,” said Skidmore.

“Different conservation practices complement each other and having them work together is a good path forward for agricultural regions.”

The full study was published in the journal Journal of the Association of Environmental and Resource Economists.

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