Measuring coastal acidification using in situ sensors in the National Estuary Program

Estuaries and coastal areas are highly vulnerable to the impacts of acidification on shellfish, coral reefs, fisheries, and the commercial and recreational industries that they support. Yet, little is known about the extent of this vulnerability and the estuary-specific drivers that contribute to acidification, such as nutrient enrichment from stormwater, agriculture and wastewater discharges, upwelling of CO2 -rich seawater, elevated atmospheric CO2 from urban and agricultural activities, benthic and marsh-driven processes, and alkalinity and carbon content of freshwater flows. Comprehensive, high resolution monitoring data are needed at varying spatial and temporal scales to provide actionable information tailored to each estuary. Because carbonate chemistry in the coastal environment can be affected by nutrient dynamics, understanding how nutrient inputs exacerbate acidification impacts is essential for the formulation of estuary-specific actions.

EPA supports coastal acidification monitoring and research in various ways (Table 1). The purpose of this report is to share EPA’s approach to long-term coastal acidification monitoring in which it initiated the use of autonomous monitoring sensors for dissolved carbon dioxide (pCO2) and pH deployed in situ in estuaries across the country through EPA’s National Estuary Programs (NEP) and their partners. This approach captures the high-resolution data that are needed to understand variability associated with acidification and ultimately to inform trends and mitigation and adaptation strategies for these vulnerable systems. This report details the plans and experiences of ten NEPs geographically distributed around the U.S. coast and their partners in conducting this monitoring over the last four years (2015–2019). The report illustrates the monitoring goals, deployment methods, data analysis, costs, preliminary results, and the role of partnerships in their successes. The preliminary results have already improved our understanding of baseline carbonate chemistry conditions in these estuaries, the factors affecting spatial and temporal variability, and the drivers responsible for changes in pCO2 and associated acidification. The sensors are successfully capturing seasonal variability and finer temporal trends that provide information on diel variability, physical processes (e.g., weather, tides), and biological activity which cannot be captured with discrete sampling alone. The preliminary data indicate that there are regional differences in the drivers of acidification, particularly the influence of upwelling events vs. land-based freshwater sources. Several of these NEPs have calculated aragonite saturation state, an indicator of conditions in which mollusk shells begin to dissolve and have identified certain vulnerable conditions for shellfish and other economically-important species in their estuaries.

Galavotti H., Vasslides J., Bohlen C., Hunt C. W., Liebman M., Hu X., McCutcheon M., Ammerman J., O’Donnell J., Howard-Strobel K., Vella P., Lehrter J., Nielsen K., Largier J., Ford T., Steele A., Yates K. K., Johnson Y., Brown C., Pacella S. R., 2021. Measuring coastal acidification using in situ sensors in the National Estuary Program. U.S. Environmental Protection Agency, Washington D. C., Document
No. EPA-842-R-21001. Report.

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