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Developing nitrogen budgets using an Integrated Biophysical Model to investigate current and future phytoplankton dynamics in a rapidly changing subtropical estuary, Barataria Basin
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  • Hoonshin Jung,
  • Melissa Baustian,
  • Ehab Meselhe,
  • Tim Carruthers
Hoonshin Jung
Water Institute of the Gulf

Corresponding Author:[email protected]

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Melissa Baustian
The Water Institute of the Gulf
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Ehab Meselhe
The Water Institute of the Gulf
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Tim Carruthers
The Water Institute of the Gulf
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Abstract

Louisiana is undergoing rapid change from natural and anthropogenic forces, such as sea level rise, subsidence, and eutrophication. Sediment diversions on the lower Mississippi River are proposed as a large-scale restoration strategy to create new wetlands and sustain existing wetland areas in Barataria Basin, Louisiana. This will introduce a large volume of sediment and nutrient rich freshwater from the Mississippi River to the receiving basins. This will result in, at least, short term changes in light and nutrient dynamics and has potential to alter phytoplankton composition. In order to understand nitrogen dynamics in Barataria Basin due to large scale coastal restoration practices, the nitrogen budgets (including particulate and dissolved forms) were calculated from outputs of the Integrated Biophysical Model, which is based on the existing Delft3D model coupled with a water quality model (D-WAQ). Creating nitrogen budgets in estuarine systems allows for better understanding of the major sources, sinks, inputs and exports across the system, increasing understanding of the amount of nitrogen available to drive estuarine primary production. Quantification of nitrogen inputs, outputs and processes is essential because it is the limiting nutrient for most estuarine primary producers (e.g., phytoplankton and emergent macrophytes). Preliminary model results for the existing conditions suggest that the dissolved inorganic nitrogen in the estuarine waters is mainly derived from diffusional sediment fluxes and mineralization of particulate organic nitrogen. Most of the dissolved inorganic nitrogen was assimilated for phytoplankton growth. A relatively small portion of dissolved inorganic nitrogen was removed from the system through denitrification in the water column. More particulate organic nitrogen originated from emergent macrophytes than from phytoplankton primary production. These model results will help better understand how proposed sediment diversions on the lower Mississippi River may change the future ecological conditions of estuarine open water in coastal Louisiana.