Are wetlands really the “Earth’s kidneys”?

Yes they are!

Healthy kidneys filter wastes and water from your body 24 hours a day. They never take a break. Soil works the same way for the earth – at least when it’s healthy.

Water from rain and snowmelt moves through the soil. When there is a heavy rainfall that water runs across the soil surface and downstream. Gentle rains soak into the soil where it is available for plant roots to take it up. But in most climates, some of that water eventually flows through the soil to the groundwater or to a stream.

stream in foreground, mountain with snow in background
Streams, like this one in the Rockies, accept snowmelt year-round. Credit: SV Fisk

As the water moves over or through the soil, it can pick up particles or chemicals present in the soil. For example, excess fertilizers from lawns or farms might be picked up. Bare soils are a big source of soil particles. Extra silt particles might get into a river from a downpour flowing over the landscape. The streaming water picks up the particles and keeps them in suspension as they flow downstream. When the water slows down – perhaps in a slow river or lake – the suspension settles out.

Even when water moves slowly, it still carries some of the smallest solids and anything that dissolves in it. If this water gets into the streams and rivers it will continue flowing and transporting its contents to lakes. It can even ultimately get to the ocean. An example of contaminants flowing over the land, into rivers, and then the oceans is the “dead zone” in the Gulf of Mexico.

Wetland in spring with hill and stream
Wetland soils and plant life are uniquely suited to help capture and filter water. Shown, Pheasant Branch Conservancy. Credit: SV Fisk

How does the environment cope with sediments and dissolved nutrients so they don’t accumulate in our rivers, lakes, and ocean? Well, just as our body cleans waste out of our blood by passing it through our kidneys, the Earth has wetlands. Wetlands are unique formations that clean solids and nutrients out of the water in our environment.

In wetlands areas, like marshes or swamps, water naturally accumulates long enough to keep the soil saturated. Wetland soils occasionally form pools as well. The vegetation of these wetlands is adapted to these saturated conditions.

The vegetation and soils work with microorganisms that naturally live in the soil. The plants and microbes often use excess nutrients as their food source. In addition, nutrients such as nitrates are converted to nitrogen gas through a microbial process called denitrification. And phosphates are absorbed by growing plants and organisms or trapped in the sediment as these plants decay.

The function of a kidney is to trap and remove waste from our bodies. Then the waste is flushed out with all the water we drink. A wetland also traps and removes waste coming to it from the environment. The water released by wetlands is cleaner than what flowed into it!

Wetlands are so effective at nutrient reduction that several states along the Mississippi River and its tributaries are working to restore wetlands. Research in Iowa says that wetlands can remove at least half of the nitrate transported to it from farms upstream.

Sandhill cranes in pond
Sandhill cranes rely on wetlands as their habitat. Shown, a pair visiting a wetland pond in Wisconsin. Credit: SV Fisk

Not only are wetlands natural filters in the environment, they also provide habitat for wildlife and areas for recreation. Because they act as these filters, they can become degraded if they are loaded with too much sediment or nutrients in the water. Restoring a degraded wetland is expensive, and creating or re-creating a watershed often means other activities, such as farming, can no longer be done.

Each of us benefits from wetlands and we can each do our part to protect them by reducing erosion and nutrient runoff in our own environments. Slowing down the storm water that runs off our houses by diverting downspouts into rain gardens will reduce erosion. Making sure your soil is covered – with plants or mulch – will reduce erosion. Cutting back on the fertilizer we use on our lawns will help keep nutrients out of the storm water that does run off our lawns and into the streams. We can do something to help our environment make the best use of the water that flows through it.

Answered by Jim Friedericks, Outreach and Education, AgSource Laboratories

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