This RAPID proposal will follow the ecosystem changes that occur as a long-disconnected floodplain of the Mississippi River at the Birds Point Levee becomes inundated with floodwaters from the historic high flows of spring 2011. The researchers will investigate ecosystem metabolism (primary production and respiration) and secondary productivity of the floodplain system during the inundation period (expected to last until end of summer 2011). The researchers will compare their findings with data on ecosystem metabolism of the river from past studies.
An event of the magnitude that is now occurring on the Mississippi River has not been seen since the 1930's (when its ecosystem effects were not studied). Extreme events like these call to question past decisions to constrain the river and prevent floodplain inundation. Research will provide a basis for evaluating alternative management strategies to accommodate extreme flooding events which may occur more frequently under future climates.
Intellectual Merit: Great rivers are the primary drainage systems of the watersheds of the world's continents. However, we know little about their function and contribution to aquatic and terrestrial ecosystems. Rivers promote biodiversity and sequester nutrients. They are intimately linked to dynamics of coastal marine systems. Large, low-gradient rivers like the Amazon, Yangtze, and Mississippi flood regularly, with huge swaths of land being historically inundated. The floodplain has long been hypothesized to contribute to river production and nutrient abatement. However, major rivers such as the Mississippi River have long been isolated by levees. In May 2011, an intentional levee breach near confluence of the Mississippi and Ohio Rivers rapidly flooded about 55,000 hectares of isolated floodplain. Another opening was made downriver. Although retention time in the floodplain was short (< 2 days), biological production, especially of native fishes, was promoted relative to the main river. Although the floodplain was agriculturally dominated, nutrients released from the floodplain were no greater than those in the main river. This research challenges that idea that flooding of farmland in the Mississippi River contributes to nutrient loading and hypoxic events in the Gulf of Mexico. Even marginal flooplain is critical for secondary production. Broader Impacts: The flood control system in the Mississippi River basin is enormous and costly, a result of an Act of Congress in 1938. As part of this system, the Birds Point-New Madrid floodway is opened if overtopping of the levee system is imminent. The activation of this system in 2011 abated flood risk both up- and down-river. However, productive agricultural land was inundated, and the upper section of the 55,000-ha area was scoured and buried by sand. Because of the short retention of water in this area, production was limited, but was stimulated. In contrast to predictions, this area was not a nutrient source nor was it a sink. When valuating these areas for flood abatement versus agricultural production, the contribution to fisheries production and reduced flooding in other portions of the river need to be assessed.
