Building wetlands along waterways best option to deter runoff from Midwest crop fields
by Tim Carpenter
The most cost-effective method of responding to chemical and sediment runoff from intense agriculture production is development of large-scale wetlands in watersheds feeding rivers and large streams, a University of Kansas researcher said in a new study.
Findings of research published in Proceedings of the National Academy of Sciences indicated the most effective environmental intervention should be concentrated at the watershed level rather than on individual farms. Conclusions were dawn from computer modeling of the Sueur River Basin in Minnesota, which is subject to runoff from corn and soybean fields.
Excess nitrogen and phosphorus can wash from fields and into waterways by rain or melting snow and can leach through the soil to groundwater. Typically, a farmer in Kansas or another Midwest state who is striving to deter soil loss and protect water quality would plant cover crops, reduce tillage, adopt high-precision fertilizer application, or add modest water retention ponds.
Amy Hansen, assistant professor of civil, environmental, and architectural engineering at KU and lead author of the study, said these useful methods of intervention relied on voluntary participation of farmers and a patchwork of government agencies. However, she said, it wasn’t as effective environmentally and less attractive economically than constructing wetlands feeding into a common waterway.
She said wetlands were beneficial because they slowed movement of water heading to streams, rivers, or lakes and contained microbes or vegetation that processed nutrients used as fertilizer on crops.
“Microbes and plants within wetlands are actually removing the nitrate from the water,” Hansen said. “With sediment, on the other hand, what the fluvial wetlands are doing is holding water back during these high flows — and by holding that water back, you’re getting lower peak stream flows, which is reducing the amount of near channel sediment that’s being transported downstream.”
Grappling with an entire watershed requires combining funds from different agencies and pinpointing locations where wetlands offer the greatest reduction in nitrates and sediments reaching waterways, said Jacques Finlay, a professor of biological sciences at the University of Minnesota.
“This work shows that we can’t make real progress toward our goals for improving water quality in agricultural areas with more of a business-as-usual approach,” Finlay said.
The proof-of-concept research funded by the NSF and involving the universities in Kansas and Minnesota as well as University of California-Irvine relied on multidisciplinary expertise of social scientists, hydrologists, ecologists, and environmental economists, said Efi Foufoula-Georgiou, of UC-Irvine.
“The sustained NSF support allowed us to take a fresh view of the problem and take the time needed to collect extensive field data, build new models, and engage with stakeholders,” Foufoula-Georgiou said.
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