Scientists examined the effectiveness of recent wetland restorations and land use conversions (set-asides) for reducing nutrients in agricultural runoff into the Iowa Great Lakes.
What are the results when scientists monitor nutrient concentrations in the inputs and outputs of restored wetlands and also monitor nutrient concentrations in the outflows of sub-watersheds differing in number of restored wetlands and acreage in set-aside programs?
Although 278 wetlands have been restored, runoff from only 20 percent of the upland areas in the Iowa Great Lakes watershed passes through these wetlands before it reaches the lakes. Wetland restorations were concentrated in areas that are no longer cultivated and consequently, most restored wetlands do not receive agricultural runoff. Where they do, restored wetlands were effective sinks for total nitrogen (TN), but their effectiveness as sinks for total phosphorous (TP) is less clear. Although the vegetation of restored wetlands is not as abundant as that in natural wetlands, this does not seem to affect their nutrient removal capacities. Concentrations of total nitrogen in outflows from sub-water-sheds with the highest number of restored wetlands and most land in set-aside programs were significantly lower than from those that were mostly crop fields. Total phosphorus concentrations in outflows, however, were highly variable, and more detailed studies are needed to determine how effective restored wetlands and set-aside programs are for reducing phosphorus in outflows.
Arnold G. van der Valk
William G. Crumpton
Year of Grant Completion
van der Valk, Arnold G. and Crumpton, William G., "Evaluating the effectiveness of restored wetlands for reducing nutrient losses from agricultural watersheds" (2004). Leopold Center Completed Grant Reports. 224.