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Streaming Service
Streaming Service
Oxbow restorations help protect Iowa's water quality
By Darcy Dougherty Maulsby
Peace and quiet define the backroads of the Iowa countryside — until you reach the rolling terrain where Purgatory Creek flows through northern Carroll County between Lanesboro and Lohrville. A robust chorus of chirping birds and croaking frogs echoes through David and Kathy Law’s pastures and fields in Jasper Township.
These creatures abound at the oxbows the Law family restored in the spring of 2022. “The oxbows help remove nitrates and improve water quality,” says Kathy, whose parents purchased the land more than 50 years ago. “We’ve also enjoyed fishing in the creek through the years and are excited to help improve the fish population and diversity in the creek.”
Purgatory Creek is a small tributary that flows into the Raccoon River, which supplies drinking water to Des Moines, notes Darrick Weissenfluh, a private lands biologist with the U.S. Fish and Wildlife Service (USFWS). Like any stream or river, Purgatory Creek is a dynamic feature of the landscape that has changed course over time. This results in U-shaped meanders, known as oxbows, that are cut off from the stream channel.
By some estimates, some individual prairie streams have more than 400 oxbows of varying size and condition. According to the Oxbow Restoration Tool Kit, an online resource funded by the Resource Enhancement and Protection (REAP) Conservation Education Program, it’s conceivable that there are tens of thousands of oxbows across Iowa's landscape. Over time, oxbows naturally fill in with sediment from runoff and stream erosion, leading to barely detectable “scars.”
“While oxbows hold about 1 million gallons of water per acre, once they fill up with sediments, they have no more water-collecting capacity,” Weissenfluh says. “The Law family’s oxbows in the pasture were former creek meanders cut-off naturally from the creek prior to the 1930s, so they’ve been filling in with sediment for a long time.”
Removing that sediment is a vital part of oxbow restoration, allowing water to collect in these areas again. “Restored oxbows are multi-purpose conservation practices that help protect water quality, control flooding, provide wildlife habitat and more,” says Brandon Iddings, a conservation services manager with the Iowa Soybean Association (ISA) Research Center for Farming Innovation.
Restoring Oxbows in Iowa for 20+ Years
The USFWS completed some of the first oxbow restorations in Iowa in 2002. Around 2020, the Law family started to consider restoring their oxbows near Purgatory Creek after they’d agreed to have an Iowa Conservation Reserve Enhancement Program (CREP) easement placed on one of their farms. (CREP provides incentives to landowners who voluntarily establish wetlands for water quality improvement in the ag tile-drained regions of Iowa.)
“The CREP easement was important from an environmental perspective to help reduce nitrates in our water system,” Kathy says. “Agencies were great to work with on that project. We were excited to learn more about the oxbow project when USFWS and ISA presented us with it.”
Restored oxbows can play a crucial role in helping achieve the goals of the Iowa Nutrient Reduction Strategy. This science- and technology-based framework assesses and reduces excess nutrients entering Iowa waters and the Gulf of Mexico. “Oxbows capture nitrates in the water from the fields and reduce those nitrate levels by 35% to 54%,” Iddings says. “Oxbows can also remove up to 100% of nitrates if the oxbows completely dry up.”
Restored Oxbows Teem with Life
Restored oxbows provide vital habitat for fish, amphibians and other wildlife that prefer slow-moving water. This is important to the USFWS, which is trying to help the endangered Topeka shiner, a small, silvery minnow.
“While Topeka shiners are thought to have lived in approximately two-thirds of Iowa streams historically, this fish is now only known to live in the Rock, North Raccoon and Boon river watersheds in Iowa,” Weissenfluh says. “The Topeka shiner is important because it’s a good indicator of a healthy, functioning ecosystem.”
However, Weissenfluh and his colleagues don’t add Topeka shiners to restored oxbows. “We wait for the fish to recolonize the oxbows — and they do,” Weissenfluh says.
Not only do restored oxbows provide essential habitat and water quality benefits, but the organic-rich soil removed during the restoration process can be spread on nearby farm fields. “Last year, our corn yielded 20 more bushels per acre in the areas where we spread soil from the oxbows,” Kathy says.
Iddings enjoys working with conservation-minded landowners like the Laws. “Since Iowa’s land is 97.2% privately owned, leaders like David and Kathy make a huge difference by showing other landowners that conservation practices, like oxbow restorations, are feasible and successful.”
Kathy is excited about the many benefits her family’s restored oxbows provide. “This area of our farm now looks more like it did 50 years ago when my mom and dad bought the property,” she says. “As Iowa farmers, we think it’s essential to preserve and protect the land for the next generation.”
