Seasonal Variability of Carbonate Chemistry in a River Influenced Eutrophic Estuary

• Main Author: Gordon, Sean P
• Format: Text
• Language: unknown
• Published: LSU Scholarly Repository 2022
• Subjects: Dissolved inorganic Carbon; Total alkalinity; Spectrophotometric pH; Ocean Acidification; Estuaries; Eutrophication; Oceanography; Ocean acidification
• Online Access: https://repository.lsu.edu/gradschool_theses/5550; https://doi.org/10.31390/gradschool_theses.5550; https://repository.lsu.edu/context/gradschool_theses/article/6630/viewcontent/Gordon_Thesis.pdf

Eutrophication is a growing problem in coastal systems due to anthropogenic activities. The increased respiration of organic matter in the water column and sediments associated with eutrophication results in increased carbon dioxide (CO2) in the water column and lowering of pH. It is well documented that estuaries and coastal waters along the Louisiana shelf in the northern Gulf of Mexico receive large amounts of nutrients from Mississippi-Atchafalaya River system that leads to eutrophication, however, there is limited information on how these processes indirectly effect water column acidification in the estuaries. In this work, we assess the seasonal and spatial variability in carbonate parameters relevant to water column acidification in the Barataria Basin, which is one of the important oyster harvesting grounds in the region. Surface and bottom water samples were collected for dissolved inorganic carbon (DIC), total alkalinity (TA), pCO2, nutrients, and dissolved oxygen (DO) along a salinity gradient across the Barataria Bay during winter, spring, summer and fall of 2021. Large seasonal variability was observed in the carbonate parameters measured. The results showed large ranges in DIC from 1553.26uM ± 381.03uM to 2593.48uM ± 216.96uM, and nitrate+nitrite, 0.2uM ± 0.15uM to 21.81uM ± 2.91uM, concentrations. The concurrent analysis of total alkalinity showed that TA distribution is influenced by various biogeochemical processes such as denitrification, sulfate reduction, and calcium carbonate precipitation that vary seasonally. This study showed that the influence of biogeochemical processes significantly deviates DIC and TA concentrations from conservative mixing processes, described as physical mixing of waves, winds, and tides. The present study also directly compared various pH measurement methodology to determine an accurate representation of pH in estuarine conditions, with spectrophotometric analysis of pH providing most robust measurements with an annual average of 7.7 5± 0.32 with a distinctly ...