Hypoxia in the Mississippi Bight: Understanding Interactions of Circulation and Biogeochemistry in a Complex River-Dominated Coastal Ecosystem

Author(s): Shiller, A.; Sanial, V.; Moore, W.

Coastal areas are key regions between the continent and the open ocean where land-derived chemical elements transported by rivers and groundwater mix with seawater. Coastal areas are very productive regions that are particularly vulnerable to human activities. The coastal waters to the east of the Mississippi River Delta, including the Mississippi Sound and Bight, are relatively understudied compared with the Louisiana Shelf to the west. Nonetheless, the Mississippi Sound and Bight contain productive fisheries, are subject to environmental issues such as oil spills, and experience seasonal hypoxia. The CONCORDE Consortium and other projects have recently been investigating this complex, river-dominated ecosystem. Because the Mississippi Sound and Bight receive fluvial inputs from various states and is comprised of both state and federal waters, potential management efforts are also complicated. In this presentation, we explore the interactions of different source waters with an emphasis on bottom water hypoxia in this system. With oxygen isotopes, we find that outflow from the Mississippi River is typically not the dominant freshwater source to the Mississippi Sound/Bight region. Furthermore, with naturally occurring radium isotopes, we observe a significant influence of submarine groundwater discharge (SGD) in bottom waters that is also correlated with hypoxic conditions. This relationship suggests that "bottom-up" influence of reduced substances on oxygen consumption can be an important contributor to hypoxia.

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