| Summary: | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Coastal and Marine Systems Science. Increasing global atmospheric CO2 concentrations drive a net flux of CO2 into the oceans, mitigating the impacts of anthropogenic greenhouse gas emissions on the climate. This results in a reduction in pH and carbonate saturation state, a.k.a. ocean acidification, of marine waters. The acidified ocean water may advect into estuaries, leading to estuarine acidification. Many estuaries are highly sensitive to this acidification due to low buffer capacity. Because estuaries provide many important ecosystem services, alterations in their carbonate systems may have significant consequences on ecosystems and the economy. Despite the current understanding that estuaries may play a disproportionately important role in global air-sea CO2 flux, little is known about carbonate systems in subtropical estuaries. Further comprehension of estuarine carbonate systems is vital for quantification of the global carbon cycle. Specifically, subtropical estuaries in the northwestern Gulf of Mexico (nwGOM) exhibit a general long-term decrease in pH and total alkalinity (TA), with lower latitudes experiencing more extreme acidification than higher latitudes. In Chapter II, sediment cores and slurries from the semiarid Mission-Aransas Estuary of the nwGOM were incubated and surface waters were analyzed for contributions of biogeochemical processes to TA change. Changes in total TA as well as calcium and sulfate ion concentration were examined following known reaction stoichiometry. Ratio of TA: ion changes suggested that carbonate dissolution co-occurred with oxidation of reduced sulfur species, and the latter consumed TA during drought periods in Mission-Aransas Estuary. This biogeochemical (sulfide oxidation) TA consumption has been poorly studied yet may affect TA budget in other semiarid estuaries worldwide. In Chapter III, river alkalinity total load and concentration were calculated ...
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