Wetlands and Water Quality

Wetlands are often viewed as filters, or kidneys of the landscape, and that’s for good reason as they have great potential for improving water quality!  Today let’s dig in and investigate how wetlands help to improve water quality and the mechanisms at work to make that happen.

Denitrification
Wetlands can be strategically placed to improve water quality through the removal of nutrients, specifically nitrate, like the wetlands in the Conservation Reserve Enhancement Program (CREP). Water enters these nutrient removal wetlands coming from a series of tile drains, often carrying a substantial load of nitrogen in the form of nitrate.

As water moves slowly through the wetland, microbes breathe in and consume nitrate (NO3), the way humans use oxygen when we breathe and respire, converting the nitrate to inert N2 gas (comprising 80% of the atmosphere).  This process is called denitrification. In turn, cleaner water is sent downstream. 

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Put simply, these wetlands are strategically designed and placed to allow the natural microbiology to happen – the microbes are doing all of the heavy lifting! These nitrate removal wetlands are ideal locations for denitrification to occur because they provide saturated anaerobic soil conditions, and the system is supplied with a source of nitrate from agricultural drainage water. Aquatic plants and wetland soils provide surfaces on which those microbes live, in addition to providing organic carbon to help maintain growth and metabolism of the denitrifying microbes. Strategically designed and sited wetlands can reduce nitrate loads to downstream water bodies by 40-70%.

Hear more about this process from Dr. Bill Crumpton and others in our award-winning video Incredible Wetlands:

Sediment Capture
Wetlands can also improve water quality by slowing the flow of water and capturing sediment, if the contributing water is coming from overland flow.  When the velocity of water slows down, as in wetlands, sediment is unable to stay suspended.  Think of it like a salad dressing with herbs and spices … when you give it a good shake, it gets well mixed throughout, but after letting it sit for some time, the herbs/spices sink to the bottom.

The same thing happens in wetlands.  When the speed of the water slows down, the suspended sediment (soil) particles gradually settle to the bottom where wetland plants hold the accumulated sediment in place, again sending cleaner water downstream.

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Role of Wetlands in Nutrient Reduction Strategy
Iowa’s Nutrient Reduction Strategy lays out several different scenarios of conservation practices in which the targeted 45% reduction in nitrogen and phosphorus can be achieved.  Wetlands play a really key role in reaching those goals, particularly on the nitrogen side of things!  One of the combined scenarios of practices calls for ~7,600 wetlands strategically placed for nitrate removal.  There are currently 77 CREP wetlands across the state of Iowa, with others in the works.

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The amount of human and financial capital to reach these goals is huge, but we continue to make forward progress in increasing the number of wetlands acres (see last week’s blog post, Wetlands: By the Numbers, for more information about ongoing wetlands restoration efforts).

Check out our previous posts celebrating American Wetlands Month:

Stay tuned next week for the fun tools and techniques we use to help teach young people about the amazing benefits of wetland ecosystems on our landscape!

Ann Staudt

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