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Quantifying the combined impacts of anthropogenic CO2 emissions and watershed alteration on estuary acidification at biologically-relevant time scales: a case study from Tillamook Bay, OR, USA
Citation:
Pacella, S., C. Brown, J. Kaldy, R. Labiosa, B. Hales, T Chris Mochon Collura, AND G. Waldbusser. Quantifying the combined impacts of anthropogenic CO2 emissions and watershed alteration on estuary acidification at biologically-relevant time scales: a case study from Tillamook Bay, OR, USA. Frontiers in Marine Science. Frontiers, Lausanne, Switzerland, 11:1293955, (2024). https://doi.org/10.3389/fmars.2024.1293955
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 from these drivers of coastal acidification can impair the fitness of coastal organisms and has negatively impacted commercial fisheries in the United States. This manuscript investigates the effects of ocean acidification and enhanced anthropogenic delivery of riverine carbon on present-day acidification dynamics of Tillamook Bay, OR (USA), part of EPA’s National Estuary Program. The study presents novel methods for parsing out oceanic versus land-based drivers of acidification in estuaries, as well as investigation of the sub-estuary-scale temporal and spatial dynamics of acidification impacts to water quality. We present our findings in the context of potential local management actions to improve riverine water quality and ameliorate coastal acidification via phytoremediation and “blue carbon” strategies. Ocean acidification was found to be responsible for >98% of anthropogenic carbon loading to Tillamook Bay, with land-based sources only contributing <2%, challenging the efficacy of strategies for ameliorating acidification via local water quality management. Our findings in Tillamook are likely relevant for many estuaries on the west coast of the United States, due to their short residence times and exposure to similar oceanic drivers of acidification.
Description:
The impacts of ocean acidification (OA) on coastal water quality have been subject to intensive research in the past decade, but how emissions-driven OA combines with human modifications of coastal river inputs to affect estuarine acidification dynamics is less well understood. This study presents a methodology for quantifying the synergistic water quality impacts of OA and riverine acidification on biologically-relevant timescales through a case study from a small, temperate estuary influenced by coastal upwelling and watershed development. We characterized the dynamics and drivers of carbonate chemistry in Tillamook Bay, OR (USA), along with its coastal ocean and riverine end-members, through a series of synoptic samplings and continuous water quality monitoring from July 2017 to July 2018. Synoptic river sampling showed acidification and increased CO2 content in areas with higher proportions of watershed anthropogenic land use. We propagated the impacts of 1). the observed riverine acidification, and 2). modeled OA changes to incoming coastal ocean waters across the full estuarine salinity spectrum and quantified changes in estuarine carbonate chemistry at a 15-minute temporal resolution. The largest magnitude of acidification (-1.4 pHT units) was found in oligo- and mesohaline portions of the estuary due to the poor buffering characteristics of these waters, and was primarily driven by acidified riverine inputs. Despite this, emissions-driven OA is responsible for over 94% of anthropogenic carbon loading to Tillamook Bay and the dominant driver of acidification across most of the estuary due to its large tidal prism and relatively small river discharges. This dominance of ocean-sourced anthropogenic carbon challenges the efficacy of local management actions to ameliorate estuarine acidification impacts. Despite the relatively large acidification effects experienced in Tillamook Bay (-0.16 to -0.23 pHT units) as compared with typical open ocean change (approximately -0.1 pHT units), observations of estuarine pHT would meet existing state standards for pHT. Our analytical framework addresses pressing needs for water quality assessment and coastal resilience strategies to differentiate the impacts of anthropogenic acidification from natural variability in dynamic estuarine systems.
