Citation:

Pacella, S., C. Brown, Jim Kaldy, J. Stecher, TChris MochonCollura, R. Labiosa, B. Hales, AND G. Waldbusser. Interactions amongst local and global drivers of coastal acidification in estuarine habitats of the northern California Current. MBARI Lecture Series, Monterrey, CA, November 07, 2018.

Impact/Purpose:

Coastal acidification is broadly defined as the lowering of pH in coastal ocean and estuarine waters as a result of human activities, including fossil fuel combustion, land use change, and eutrophication. Water quality impacts due to eutrophication-enhanced coastal acidification have been studied in a variety of coastal systems, including the Chesapeake Bay, the Gulf of Mexico, the northeast coast of the United States, but little work has been done to understand the dynamics of this process in west coast estuaries. This is despite the large documented impacts of coastal acidification on the productivity of the west coast shellfish aquaculture industry, where over half of surveyed industry stakeholders have expressed that coastal acidification is currently affecting their business. Therefore, there is a need to understand the role of watershed delivery of nitrogen and co-pollutants in current coastal acidification. This project estimates the contributions of human-driven changes in ocean and watershed chemistry to quantify the magnitude and timing of changes in pH in two seagrass habitats of Puget Sound, WA. Our analysis estimates present-day departures in pH driven by local versus global anthropogenic drivers, and therefore provides constraints on the relative effectiveness of local water quality management to mitigate coastal acidification in these habitats.

Description:

Recent studies have begun to explore physical and biogeochemical mechanisms of carbonate chemistry variability in a variety of coastal habitats, including coral reefs, upwelling margins, and inland seas. To our knowledge, there have been limited mechanistic studies of annual carbonate chemistry variability in nearshore estuarine environments. Here, we present autonomous sensor and grab sample data of carbonate chemistry from a 10-month period within two subtidal seagrass beds in Possession Sound, WA. Simple mass balance stoichiometric models were used to evaluate seasonal drivers of carbonate system parameters in the seagrass beds. Simulations of increasing anthropogenic carbon (Canth) burdens in the habitats revealed seasonal differences in the magnitude of carbonate system responses. The addition of Canth alters the thermodynamic buffer factors (e.g., the Revelle factor) of the carbonate system, decreasing the system’s ability to buffer natural variability in the seagrass habitat on high-frequency (e.g., tidal, diel) and seasonal timescales. As a result, the most harmful carbonate system indices for many estuarine organisms (minimum pHT, minimum Ωarag, and maximum pCO2(s.w.)) change rapidly with increasing Canth. We highlight how the observed seasonal climatology and non-linear response of the carbonate system to increasing Canth drive the timing of the crossing of established physiological stress thresholds for endemic organisms, as well as thresholds relevant for water quality management. In this system, the relative benefits of the seagrass beds in locally mitigating ocean acidification during the growing season increase with the higher atmospheric CO2 levels predicted toward 2100. Presently, however, these mitigating effects are mixed due to intense diel cycling of CO2 driven by community metabolism.

Record Details: