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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. Wetland Management Reduces Sediment and Nutrient Loading to the Upper Mississippi River. Dennis Corwin (ed.), JOURNAL OF ENVIRONMENTAL QUALITY. American Society of Agronomy, MADISON, WI, 42(2):573-583, (2013).
Our objectives were to determine 1) the effectiveness of a restored wetland to meet management goals of sediment and nutrient retention under a range of hydrological conditions, 2) the effectiveness of a restored wetland to retain sediment and nutrients compared to an adjacent natural wetland, and 3) the effectiveness of removal of nitrogen and phosphorus by way of soil excavation compared to natural biogeochemical processes.
Restored riparian wetlands in the Upper Mississippi River basin have the potential to remove sediment and nutrients from tributaries before they flow into the Mississippi River. For 3 yr 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 Upper Mississippi. We measured sediment, N, and P 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 y-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 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.