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COASTAL AND MARINE SYSTEM SCIENCE PROGRAM
DEPARTMENT OF PHYSICAL AND ENVIRONMENTAL SCIENCES
TEXAS A&M UNIVERSITY-CORPUS CHRISTI
SUBJECT: Spatial and temporal trends and controlling factors of carbonate chemistry in the estuaries of the northwestern Gulf of Mexico
MAJOR ADVISOR: Dr. Xinping Hu
ABSTRACT
Estuarine carbonate chemistry is an important field of study because of its ties to coastal acidification (and associated ecological and economic impacts) as well as regional carbon budgets. This dissertation investigated the temporal and spatial variability in carbonate chemistry in estuaries of the northwestern Gulf of Mexico (nwGOM) as well as the relationships between the carbonate system and other environmental parameters. First, a four-decade dataset that spans seven estuaries along a latitudinal gradient was used investigate long-term trends in calculated carbonate system parameters. Partial pressure of CO2 (pCO2) was generally increasing, and rates indicated that the estuaries have become an increasing source of CO2 to the atmosphere. Saturation state of aragonite (ΩAr) was generally decreasing across the region, suggesting that carbonate chemistry has become less suitable to calcifying organisms. Next, diel and seasonal variability in pH and pCO2 at a tidal inlet was assessed; variability was substantial over both timescales, though fluctuations were smaller than many other regions. Data from co-located environmental sensors suggested that temperature, net community metabolism, tidal fluctuations, and freshwater inflow all exerted important controls on the carbonate system, and pCO2 was among the most important of many environmental parameters to distinguish between seasons and between day/night conditions. Finally, the last chapter investigated carbonate system dynamics in an estuary that experiences periodic summertime hypoxia. There was a positive relationship between pH and dissolved oxygen; however, hypoxic conditions did not result in critically low pH as it has in other systems. The high buffer capacity was attributed to strong evaporation and high productivity in adjacent seagrass meadows, highlighting the importance of intrinsic buffer capacity on the extent of hypoxia-induced acidification. Together, the work of this dissertation demonstrates that the carbonate chemistry in the nwGOM estuaries is more suited to support calcifying organisms than many other estuarine environments, but reduction in freshwater inflow and rising ocean acidification could both lead to estuarine acidification, hence mitigation efforts may be needed in the future.
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