RAPID: Sediment, water, and nutrient flux and fate in Lake Pontchartrain from the 2011 Bonnet Carre Spillway Opening.

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RAPID: Sediment, water, and nutrient flux and fate in Lake Pontchartrain from the 2011 Bonnet Carre Spillway OpeningEAR-1139997Samuel Bentley, Sibel Bargu, Chunyan Li, Nan Walker, John R. WhiteLouisiana State UniversityABSTRACTThe lower Mississippi River Delta (MRD), inhabited by 2 million people, is a critical national resource in terms of maritime transport, fisheries, and energy. MRD wetlands and waters are degrading at alarming rates, losing wetlands equivalent to the area of Delaware since the 1930?s, and more over the next century. The health of coastal waters and the fate of wetlands are strongly governed by the flow of fresh water and accompanying sediments and nutrients, which are now largely controlled by engineered structures along the river. For these reasons, conservation and restoration of the MRD is one of the outstanding environmental and socioeconomic challenges faced by our country over the next century. Understanding and managing water, sediment, and nutrient flux and fate into the MRD coastal zone is central to this challenge. The Spring 2011 hydrograph of the Mississippi River is reaching levels exceeding the Great Flood of 1927 in many locations in Louisiana. To provide relief to river levees, water is being released through the Bonnet Carré Spillway (BCS) into Lake Ponchartrain (LP), a large mostly enclosed estuary within the MRD (Fig. 1). BCS opening on May 9 is now producing record fluxes of water (8800 m3 s-1, 126% of design capacity) into LP, likely along with record fluxes of sediment and nutrients. Understanding the dynamics and impact of this plume in LP is important for several reasons: (1) nutrient loading to the lake will produce potentially toxic algal blooms; (2) fresh water flux will cause strong exchange of the fresher lake with the saltier coastal ocean; and (3), measurement and study of sediment supply and deposition will provide important information for use of sediment in engineered diversions for delta restoration. PIs will sample water, sediment, nutrients, and plankton over time to understand impacts to the lake, in order to better understand impacts from future manmade diversions for delta restoration. Because LP has strong similarities to other MRD estuaries, and engineered diversions of river water and sediment are primary tools planned for MRD conservation and restoration, results of this work will be directly applicable to large regions of the MRD in need of conservation and restoration.