Nutrient retention on the Upper Mississippi River Floodplain

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Nutrient Cycling in Aquatic Ecosystems

Rivers have a natural capacity to improve water quality when they are connected to their natural floodplains and are not overloaded with sediment and nutrient runoff. Where rivers have been disconnected from their historical floodplains and channelized to eliminate backwater areas, increased flow and nutrient loads have contributed to local and downstream problems of excessive nutrient enrichment. For example, high nutrient loads from the Upper Mississippi River have contributed to a large hypoxic zone in the Gulf of Mexico each summer. Allowing rivers to flood their historical floodplains may reduce the nutrient loads by trapping sediment and nutrients on the floodplain. Understanding how the reconnection of rivers with their floodplains affects nutrient cycling is important for managers trying to improve water quality.

USGS scientists measuring sand deposition from a summer flood on the Upper Mississippi River near La Crosse, Wisconsin

USGS scientists measuring sand deposition from a summer flood on the Upper Mississippi River near La Crosse, Wisconsin

(Credit: Lynn Bartsch, USGS - Upper Midwest Environmental Sciences Center. Public domain.)

The goal of this research is to quantify the retention of sediment, nitrogen, and phosphorus on floodplains in the Upper Mississippi River System. Studies have been conducted on the floodplain of the Mississippi River and in small tributaries in Wisconsin and Iowa to measure the potential to remove these pollutants before they enter the main Mississippi River channel.

USGS scientist collecting a soil sample on the Upper Mississippi River floodplain near La Crosse, Wisconsin.

USGS scientist collecting a soil sample on the Upper Mississippi River floodplain near La Crosse, Wisconsin.

(Credit: Rebecca Kreiling, Upper Midwest Environmental Sciences Center. Public domain.)