Characteristics of the Carbonate System in a Semiarid Estuary that Experiences Summertime Hypoxia
In oceanic environments, two sources of CO2 have been found to contribute to acidification of stratified water bodies, i.e., CO2 invasion due to anthropogenic atmospheric CO2 increase and respiration-produced CO2 from organic matter remineralization. Acidification caused by these CO2 sources has been observed frequently in numerous environments spanning from open continental shelves to enclosed estuaries. Here, we report observations on carbonate system dynamics in a relatively well-buffered lagoonal estuary, Corpus Christi Bay (CCB), in a semiarid subtropical region that is influenced by summertime hypoxia as well as strong evaporation and seagrass vegetation in the vicinity. While the relationship between dissolved oxygen (DO) and pH in the bottom waters of CCB was positive as in other coastal and estuarine environments prone to hypoxia, the slope was significantly less than in other systems. We attribute the high buffering capacity in CCB to the presence of abundant seagrass meadows adjacent to CCB and strong evaporation-produced density flow that delivers low CO2 waters to the bottom of CCB. Thus, despite the occurrence of hypoxia, neither bottom water carbonate saturation state with respect to aragonite (Ωarg) nor CO2 partial pressure (pCO2) reached critical levels, i.e., undersaturation (i.e., Ωarag<1) or hypercapnia (pCO2>1000 µatm), respectively.
KeywordsHypoxia Estuarine acidification Ocean acidification Seagrass CO2
We thank H. Wang, H. Yao, R. Kalk, L. Hyde, T. Palmer, and E. Morgan for their help with field sampling, and L. Adams for her help with nutrient analysis. We also acknowledge NSF (OCE no. 1654232) for the support during the development of this manuscript. Two anonymous reviewers offered critical comments that helped to improve the quality of this manuscript.
Texas Research Development Fund from the Office of Research, Commercialization, and Outreach of Texas A&M University – Corpus Christi sponsored our initial exploratory work in 2015. The 2016 study was funded by NOAA’s NOS National Center for Coastal Ocean Science (Contract No. NA15NOS4780185).
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