Proceedings of the 2019 Mississippi Water Resources Conference

Year: 2019 Authors: Swarzenski C.M., Rodgers K.D., Mize S.V.

The U.S. Geological Survey and U.S. Environmental Protection Agency have begun a preliminary assessment of seasonal and annual salinity trends in the Mississippi Sound, an area that extends from Mobile Bay in Alabama to Bayou Rigolettes in Louisiana. On the south, the Sound is separated from the Gulf of Mexico by a series of barrier islands. These islands allow the exchange of water between the Gulf and Mississippi Sound through a series of tidal passes. The Pascagoula and Pearl Rivers along with a few smaller rivers locally introduce the majority of freshwater into the Sound. Freshwater may also enter the Sound through Lake Pontchartrain during openings of the Bonnet Carre spillway. Extreme weather events such as tropical storms and heavy rainfall further influence salinity.

Annual and seasonal trends in salinity and freshwater inflow from local watersheds are being evaluated using Kendall-Tau analysis. Stations from Mobile Bay, the Mississippi Sound and the nearshore waters of eastern coastal Louisiana are included. Not surprisingly, salinity in the Mississippi Sound, and by extension, water-quality are controlled by the timing and quantity of freshwater input and the rate of lateral exchange of water along the coasts of Alabama, Louisiana, and Mississippi. Salinity is a determining factor for productivity in estuarine waters and understanding the factors that control salinity variability are fundamental to understand biological functioning and health, as well as, source water partitioning in the Mississippi Sound.