A few years back, a pilot project called the Integrated Wetland Landscape Systems Initiative, a.k.a. the “Iowa Plan,” was set up to study a potential strategy for improving water quality. Its driving question: how effective are wetlands in reducing nitrogen loads from upgraded drainage systems?
Results are in, and here to present and explain them is Dr. William Crumpton, wetland ecologist at Iowa State University, with this week’s webinar: “Integrating Drainage Improvements and Wetland Restoration in Iowa: Environmental Impacts of Improved Drainage and Targeted Wetland Restoration.”
Dr. Crumpton begins by reviewing the urgency behind this work: due in part to the nutrients that end up in Iowa’s agricultural drains, the state has high nitrate concentrations in its surface waters. This makes Iowa a major contributor to gulf hypoxia; the Iowa Nutrient Reduction Strategy goal is a 45% reduction in N loads (41% from non-point sources).

At five agricultural sites, the Iowa Plan redesigned and upgraded tile such that, instead of water draining to an off-site mitigation bank, it went instead through an on-site, permanently protected wetland. Five reference sites, without drainage upgrades but with CREP wetlands, were also included for comparison. Nutrient concentrations were measured using automated samplers at the inflow and outflow, sampling the water every six hours.
The findings, now brought together after some years of data collection, are promising for wetlands. On the pilot sites, improved drainage led to less drowned-out soil than the reference sites suffered from, but did not significantly increase N export, P export, nutrient concentrations, or mass loads. The wetlands on these sites continued to successfully intercept whatever was thrown at them, reducing nitrate and total N loads downstream by about 30%, just as would be expected for an Iowa CREP wetland.
Notably, the five pilot project wetlands cover just 68 acres together, but intercept more than 9,000 acres of agricultural drainage. So, given the 30% decrease they provide, those 68 acres are doing the nitrogen reduction work we’d get by retiring some 2,700 acres of cropland.
For the fully nuanced data, further details, and a lively Q&A session, you can watch the recording of Dr. Crumpton’s webinar here, and catch up with all our previous webinars on the ILF website.