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Wetland management reduces sediment and nutrient loading to the Upper Mississippi River

Kreiling, R. M., J. P. Schubauer-Berigan, W. B. Richardson, L. A. Bartsch, P. E. Hughes, J. C. Cavanaugh, and E. A. Strauss.  2013.  Wetland management reduces sediment and nutrient loading to the Upper Mississippi River.  Journal of Environmental Quality 42:562-572.

Abstract

Restored riparian wetlands in the Upper Mississippi River basin have potential to remove sediment and nutrients from tributaries before they flow into the Mississippi River. For 3 years we calculated retention efficiencies of a marsh complex, which consisted of a restored marsh and an adjacent natural marsh that were connected to Halfway Creek, a small tributary of the Mississippi. We measured sediment, N, and P removal through a mass balance budget approach, N removal through denitrification, and N and P removal through mechanical soil excavation. The marsh complex had average retention rates of approximately 30 Mg sediment ha−1 yr−1, 26 kg total N ha−1 yr−1, and 20 kg total P ha−1 yr−1. Water flowed into the restored marsh only during high-discharge events. Although the majority of retention occurred in the natural marsh, portions of the natural marsh were hydrologically disconnected at low discharge due to historical over-bank sedimentation. The natural marsh removed >60% of sediment, >10% of P, and >5% of N loads (except the first year, when it was a N source). The marsh complex was a source of NH4+ and soluble reactive P.  The average denitrification rate for the marsh complex was 2.88 mg N m−2 h−1. Soil excavation removed 3600 Mg of sediment, 5.6 Mg of N, and 2.7 Mg of P from the restored marsh. The marsh complex was effective in removing sediment and nutrients from storm flows; however, retention could be increased if more water was diverted into both restored and natural marshes before entering the river. Partial funding by UMRR-EMP LTRMP leveraged with funding by an Interagency Agreement between the USEPA and the USGS (DW14996301)

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