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Floodplain restoration enhances denitrification and reach-scale nitrogen removal in an agricultural stream
Citation:
Roley, S. S., J. L. Tank, M. L. Stephen, L. T. Johnson, J. J. BEAULIEU, AND J. D. Witter. Floodplain restoration enhances denitrification and reach-scale nitrogen removal in an agricultural stream. ECOLOGICAL APPLICATIONS. Ecological Society of America, Ithaca, NY, 22(1):281-297, (2012).
Impact/Purpose:
To inform the public.
Description:
Streams of the agricultural Midwest export large quantities of nitrogen, which impairs downstream water quality, most notably in the Gulf of Mexico. The two-stage ditch is a novel restoration practice, in which floodplains are constructed alongside channelized ditches. During high flows, water flows across the floodplains, increasing benthic surface area and stream water residence time, as well as the potential for nitrogen removal via denitrification. To determine two-stage ditch nitrogen removal efficacy, we measured denitrification rates in the channel and on the floodplains of a two-stage ditch in north-central Indiana for one year before and two years after restoration. We found that in-stream rates were similar before and after the restoration, and they were influenced by surface water NO3 - concentration and sediment organic matter content. Denitrification rates were lower on the constructed floodplains, and were predicted by soil exchangeable NO3 - concentration. Two-stage ditch restoration contributed significantly to NO3 removal, especially during storm events. Because of the high NO3 loads at our study site, the increase in NO3 - removal still translated to less than 10% of the NO3 - load, with the highest percent removal occurring at the lowest loads. Therefore, the two-stage ditch’s effectiveness at reducing downstream N loading will be maximized when the practice is coupled with efforts to reduce N inputs from adjacent fields.
