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Tuesday, January 26 • 11:00am - 11:20am
Quantifying The Effect of Floodplain-River Connectivity: Sediment, Nitrogen, Phosphorus and Carbon Removal Via Flooding on The Maquoketa River Floodplain, Iowa

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AUTHORS: W.B. Richardson*, US Geological Survey, Upper Midwest Environmental Sciences Center; G. Nalley, USGS Iowa Water Science Center; L. Bartsch, US Geological Survey, Upper Midwest Environmental Sciences Center; R. Kreiling, US Geological Survey, Upper Midwest Environmental Sciences Center; J. Garrett, USGS Iowa Water Science Center; S. Bailey, US Geological Survey, Upper Midwest Environmental Sciences Center

ABSTRACT: Ecosystem services provided by floodplains include removal of nitrogen, phosphorus, and sediments, and sequestration of carbon. Effectiveness of floodplains in providing these services is dependent on the extent and location of the connection between floodplain and river. Tributary loading of sediments, nitrogen, and phosphorus to the Upper Mississippi River contributes to the development of river and coastal eutrophication as well as hypoxic conditions in the Gulf of Mexico. Recent research has shown that management of river connectivity of channels to floodplains is an effective mitigation strategy to remove nutrients, sediment, and carbon from rivers. Here, we measured deposition of nitrogen, phosphorus, carbon and sediment with clay marker horizons in a recently reconnected floodplain of the Maquoketa River, IA, near the confluence with the Mississippi River. We also measured ambient denitrification and potential denitrification on the floodplain prior to and after flooding, beginning in October 2014 and in March and May 2015. There was one inundation event during this period with relatively short duration (days). Load of nitrate was also estimated during the year beginning October 1, 2014. Total annual nitrate load was 8,450 Mg NO3--N and peak transport during the inundation event was 110 Mg/d (+/- 8.0% SE). On this 93 ha floodplain, 700 Mg sediment, 12.0 Mg carbon, 1.16 Mg nitrogen, and 0.51 Mg phosphorus were deposited over the study period. River derived N deposited on the floodplain represented ~0.015 percent of the annual N load, or ~0.39% of the event transport (3 days). Denitrification removed NO3--N ranged from 250 kg d-1 (March 2015) to 668 kg d-1 (October 2014). This study highlights the nutrient and sediment removal capacity of a single, relatively small connected floodplain – higher removal rates would result from larger floods of longer duration or larger breaks in surrounding levees. Nitrate loss via floodplain denitrification, while highly variable represents a permanent loss of nitrogen from this catchment.

Tuesday January 26, 2016 11:00am - 11:20am EST
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