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Watershed Controls of Acidification Dynamics in Estuaries of the United States: from Case Study to National Assessment
Citation:
Pacella, S., Cheryl A. Brown, Jim Kaldy, R. Labiosa, B. Hales, TChris MochonCollura, AND G. Waldbusser. Watershed Controls of Acidification Dynamics in Estuaries of the United States: from Case Study to National Assessment. 5th International Symposium on the Ocean in a High CO2 World, Lima, N/A, PERU, September 12 - 16, 2022.
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 estuary pH in Tillamook Estuary, OR. Tillamook Estuary has been identified as an estuary of national significance as part of the US EPA’s National Estuary Program, and is home to extensive shellfish aquaculture and agricultural industries. Our estimates of the watershed’s role in altering estuary pH will help inform the effectiveness of potential nutrient and co-pollutant management strategies on improving water quality in the estuary. We also outline how methods developed in this case study are being utilized in a new nationwide assessment of U.S. estuaries’ vulnerability to land-based drivers of acidification.
Description:
The human modification of carbon and nutrient transport from land to sea is recognized as an important driver of acidification in coastal and estuarine systems. However, there are few studies quantifying these land-based impacts on space and time scales relevant for informing: 1) likely impacts to endemic organisms, and, 2) the potential efficacy of management actions operating at local versus global scales. To address these questions, we present a case study of Tillamook Estuary, OR (USA), a small open-coast estuary in the northern California Current Large Marine Ecosystem subject to coastal upwelling and river discharge from an agriculturally-developed watershed. From July 2017 through July 2018, we conducted a series of sampling cruises to characterize the CO2 biogeochemistry of the estuary, coastal ocean, and riverine end-members. We quantified the roles of allochthonous input of oceanic and riverine dissolved inorganic carbon (DIC), as well as autochthonous estuary carbon cycling, in controlling the seasonal pH, CaCO3 saturation state, and pCO2 dynamics of the estuary. Variability in the ocean and riverine end-members was the primary control on estuarine CO2 chemistry, while autochthonous cycling acted as a seasonally variable sink and source of DIC. Riverine DIC levels were highest in areas of increased agricultural activity and hypothesized to be driven by human land use change. Observed riverine DIC enrichments were combined with published estimates of oceanic anthropogenic carbon burdens to estimate the magnitude and timing of human changes to present-day CO2 chemistry in the estuary. Most of the perturbation in estuarine chemistry was due to ocean acidification-driven changes in the ocean waters advected into the estuary. We also present an overview of a new project aimed at assessing the relative vulnerability of United States estuaries to these anthropogenic changes in coastal watershed carbon and nutrient delivery.