The diversion of nutrient-rich water through forested wetlands--especially within the Lower Mississippi River Basin?is one proposed approach to reduce nutrient export to coastal estuaries. The primary objective of this research is to quantify nutrient retention and carbon mineralization as river water is transported through the Atchafalaya Basin Floodway System (ABFS). By characterizing water transported via channelized sections of the basin in contrast to the un-channelized spillway including the forested swamps, the research team expects to find enhanced nutrient removal within water diverted through the spillway due to increased residence time and enhanced contact with floodplain sediments. Samples will be collected across the basin over the flood period (12 weeks). Water isotopes and conservative anions will be measured to quantify water sources and infer water residence time. Nutrients (phosphorus and nitrogen species) will be measured to quantify system processing and delineate spatial differences across the ABFS.
Although diverting water is a proposed approach to reduce nutrient export, and associated hypoxic zone extent, in the Gulf of Mexico, the effect of very large-scale diversion on the magnitude of nutrient reduction is not well understood. The current flooding in the Lower Mississippi (highest levels since 1927) has resulted in the Army Corps of Engineers opening the Morganza Spillway into the ABFS for the first time since 1973. The opportunity to explore the fate of the nutrient-rich Mississippi water through the ABFS is unprecedented and will provide valuable insight into the coupling of hydrology and biogeochemistry of the Atchafalaya River and Floodplain. This study will provide insights on nutrient reduction associated with large scale diversion of spring runoff water.
Floodwater diversions are used to mitigate property loss to downstream communities, but are also another approach to mitigate excess nutrient delivery to coastal estuaries. Although this approach has been proposed as one option to reduce nutrient export from the Mississippi River basin, few observations have been made to determine the effectiveness of large-scale diversions. We found during an unprecedented flood the effects of transported riverine water into a large swamp. Our findings support this approach in addressing excess nutrients, and alleviated fears severely low oxygen induced by nutrient rich river water within backwater regions of the swamp. Results from the project are being shared with the state of Louisiana for decision management within the Atchafalaya flood basin. Our results will contribute to understanding the impacts of floodwater diversions, which can alleviate flooding and reduce nutrient export to sensitive coastal areas which large numbers of people rely on for the livelihood. The 2011 flood in the Lower Mississippi (highest levels since 1927) resulted in the opening the Morganza Spillway into the Atchafalaya Basin Floodway System (ABFS) for the first time since 1973. This event provided the opportunity to examine nutrient cycling during the hydrologic transport of nutrient-rich Mississippi River water throughout the ABFS. Samples were collected across the basin over the flood period (12 weeks). Conservative (water isotopes and anions) and non-conservative solutes (carbon and nitrogen) were analyzed to quantify water sources, infer water residence time, and quantify nutrient retention. The opportunity to explore the fate of this nutrient-rich water through the ABFS was unprecedented, and is expected to provide valuable insight into the hydrology and biogeochemistry of floodplains such as the ABFS and ultimately the potential for reducing nutrient export to the Gulf of Mexico.
