Examining the Impact of Bonnet Carré Spillway Opening on Hypoxia Evolution in the Mississippi Sound and Bight: A 2019 Case Study

<p>In 2019, the Bonnet Carré Spillway (BCS) was opened twice, releasing unprecedented volumes of low-salinity, highly polluted water from the Mississippi River into the Mississippi Sound and Bight (MSAB). These events dramatically altered the region's salinity, circulation, and ecological conditions, raising concerns about their role in hypoxia formation. This study uses a high-resolution, coupled physical-biogeochemical component of the Mississippi Sound and Bight Coupled Ocean Atmosphere Water Sediment Transport (msbCOAWST) model to explore how BCS discharges influence the development and distribution of low-oxygen waters in the MSAB. Two model scenarios were simulated, which include a baseline with natural riverine inputs only (RO) and a second incorporating both riverine and BCS freshwater inputs (RO+BCS). The model’s accuracy was evaluated using in situ observations of temperature and salinity, showing strong agreement, particularly for temperature (r² > 0.9). Results indicate that BCS inflows enhanced stratification within the MSAB and strengthened two-layer circulation, rapidly freshening surface waters while isolating oxygen-poor bottom layers. Biogeochemical responses showed increased nitrate import from the shelf and greater export of ammonium, detritus, and phytoplankton from the Sound to the shelf, reflecting intensified nutrient cycling and oxygen demand. Biweekly flux analyses through key tidal inlets such as Cat Island Channel, Ship Island Pass, and Dog Key Pass revealed amplified shelfward transport of organic matter and low-oxygen water during peak discharge. Spatial and vertical patterns of bottom dissolved oxygen and detritus demonstrated that BCS effects were time-dependent, with enhanced mixing and re-oxygenation during openings followed by renewed hypoxia as stratification re-established. So, the BCS acted as both a ventilator and amplifier of hypoxia, showing how episodic diversions can simultaneously enhance productivity and degrade oxygen conditions.</p>

Name thesis:degree_name

Master of Science (MS)

Level thesis:degree_level

Masters Thesis

Year dc:date.available

2026

Author dc:creator

• Ajibade, Hameed Jimoh

Contributors dc:contributor

• Dr. Jerry Wiggert
• Dr. Mustafa Kemal Cambazoglu
• Dr. Scott P. Milroy

• BONNET CARRÉ SPILLWAY
• BCS
• msbCOAWST
• ROMS
• BGC
• Hypoxia
• Mississippi Sound and Bight
• nGOM
• NPZD
• Biogeochemistry
• Dissolved Oxygen
• DO
• Earth Sciences
• Environmental Health and Protection
• Environmental Monitoring
• Environmental Sciences
• Geochemistry
• Geology
• Geomorphology
• Oceanography
• Oceanography and Atmospheric Sciences and Meteorology
• Other Oceanography and Atmospheric Sciences and Meteorology

Repository record dc:identifier

https://aquila.usm.edu/masters_theses/1178

OAI identifier oai:identifier

oai:aquila.usm.edu:masters_theses-2272