Kay Stefanik | Assistant Director, Iowa Nutrient Research Center
Happy American Wetlands Month! May is a wonderful time to recognize and celebrate all the benefits that wetlands provide to humans and the environment. Wetland plants are beginning to bring a lush green back to the landscape, complementing the serene blue water that has been present in many areas since late winter. With the new plant growth comes the familiar sights and sounds of increased animal activity. Take a walk around a wetland this month and you are likely to see and hear flocks of migratory waterfowl, red-winged blackbirds, leopard frogs, and maybe even catch a glimpse of a painted turtle.
It is easy to see that wetlands provide wildlife habitat and recreational opportunities, but they also provide benefits that are harder to observe. Wetlands help to retain water after rain and large storm events, which can contribute to a decrease in flooding downstream. Wetlands also help to improve water quality by reducing sediment and nutrient loads. Through a process called denitrification, microorganisms in wetland sediment take up nitrate dissolved in water and convert it to nitrogen gas. This nitrogen gas is lost to the atmosphere, which is about 78% nitrogen, effectively preventing the nitrate from moving into other surface waters where the nitrate could have contributed to increased algal growth or even harmful algal blooms.
For landowners and farmers looking to reduce nitrate loss from their row crop acres, wetlands are an effective practice that not only improves water quality, but also adds beauty, wildlife habitat, and floodwater storage. There are multiple types of wetlands that can be used to reduce nitrates, including the traditional CREP nitrate removal wetlands, multipurpose oxbow wetlands, pothole wetlands in low profitability zones of fields, and tile zone wetlands.
Many people are likely familiar with CREP wetlands. CREP wetlands are constructed in the Des Moines Lobe, an area of land that was once a mosaic of prairie and wetland habitat formed during the last glaciation event. Today, the Des Moines Lobe is predominantly an agricultural landscape underlain with an extensive network of tile drainage. Tile drainage water is diverted into CREP wetlands to reduce nitrate loads leaving the field. Wetlands that receive tile drainage water have been shown to reduce nitrate loads by an average of 52%.
Gaining popularity in Iowa are multipurpose oxbows, a practice approved for nitrate reduction by the Iowa Nutrient Reduction Strategy Science Team in 2019. Oxbows are wetlands that form when a meander of a stream gets cut off, either naturally or artificially, from the main channel. Oxbow wetlands would normally only receive large inputs of water during flood events, when the river overflows its banks and floods the oxbow. Multipurpose oxbow wetlands are a little different as they are restored and designed to have an additional water source, water from tile drainage. This tile drainage water carries dissolved nitrate that is then removed through the process of denitrification within the wetland. In addition to reducing nitrate, the wetlands also serve as important habitat for fish, such as the Topeka shiner, making them multipurpose in the sense that the act as both treatment wetlands and wildlife habitat.
While less common, it is also possible to situate a wetland on row crop acres that are frequently too wet to be considered profitable. These low spots in fields can accumulate higher concentrations of phosphorus and nitrate due to surface runoff and subsurface water flowing into the area. By planting wetland vegetation and converting the land to a wetland, conditions in the soil can favor microbial denitrification, helping to reduce nitrate loss from the field. Nitrate removal of wetlands situated in wet spots can be increased by diverting tile drainage water into them. These wetlands are referred to as tile zone wetlands. As current research improves our understanding and the effectiveness of these types of wetlands, we will likely see more popping up around Iowa.
Wetlands are an effective tool that can help Iowa reach the 45% nutrient reduction goal laid out in the Iowa Nutrient Reduction Strategy. If you are looking for a nitrate reduction practice that also has wildlife habitat, can help with floodwater retention, and increases the beauty of your property, I recommend considering a wetland.
Once again, happy American Wetlands Month. I hope you all get the chance to visit a wetland and enjoy the benefits wetlands provide.
Iowa Learning Farms 