Freshwater Endmembers Impacting Carbonate Chemistry in the Mississippi Sound

• Main Author: Savoie, Allison
• Format: Text
• Language: unknown
• Published: The Aquila Digital Community 2020
• Subjects: ocean acidification; carbon chemistry; rivers; oyster reefs; carbonate system; Biogeochemistry; Environmental Chemistry; Oceanography; Ocean acidification
• Online Access: https://aquila.usm.edu/masters_theses/761; https://aquila.usm.edu/context/masters_theses/article/1812/viewcontent/auto_convert.pdf

Coastal ecosystems are highly dynamic areas for carbon cycling and are likely to be negatively impacted by increasing ocean acidification. This research focused on dissolved inorganic carbon (DIC) and total alkalinity (TA) in the Mississippi Sound in order to understand the influence of local rivers that supply alkalinity to the area and buffer against ocean acidification. This area receives large fluxes of freshwater from local rivers, in addition to episodic inputs from the Mississippi River through a human-built diversion, the Bonnet Carré Spillway. Sites in the Mississippi Sound were sampled monthly during August 2018 to November 2019 and at weekly frequency during June–August 2019 in response to an extended spillway opening. Prior to the 2019 spillway opening, the contribution of the local, lower alkalinity rivers to the Mississippi Sound may have left the system more susceptible to ocean acidification during winter months, with aragonite saturation states < 2. After the spillway opened, despite a large increase in TA throughout the Mississippi Sound, aragonite saturation states remained low, likely due to hypoxia and increased CO2 concentrations in subsurface waters. Throughout the study period, the Mississippi Sound generally acted as source for CO2 to the atmosphere, with decreased flux after periods of increased river discharge. Increased Mississippi River input could represent a new normal in the Mississippi Sound’s hydrography during spring and summer months as the spillway has been utilized more frequently in recent years. The observed fluctuations in saturation states and alkalinity conditions may be detrimental to future oyster stocks along the Mississippi coastline.