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Snohomish RARE summary slides for Interagency Working Group on Ocean Acidification
Citation:
Pacella, S. Snohomish RARE summary slides for Interagency Working Group on Ocean Acidification. Interagency Working Group on Ocean Acidification, Washington, DC, March 06, 2017.
Impact/Purpose:
This study is part of a RARE project with Region 10 focused on the role of local drivers (natural and anthropogenic) in controlling the carbonate chemistry dynamics in a nearshore estuarine environment. Multiple processes, including primary production and respiration, river runoff, cultural eutrophication, oceanic upwelling, and atmospheric exchange contribute to the characteristically dynamic carbonate conditions in these habitats, with potential interactions amongst these processes leading to coastal acidification. As a result, the impact of coastal acidification to productive, nearshore estuarine environments remains poorly characterized, despite these areas being some of the most economically, ecologically, and culturally important habitats in the marine waters. Local nutrient inputs have the potential to exacerbate coastal acidification by stimulating enhanced production of organic matter, and subsequent increases in local respiratory CO2 release. Quantifying baseline biological rates and habitat-specific carbonate chemistry dynamics is necessary to attribute any additive/synergistic effects of anthropogenic nutrient inputs to the system in contributing to coastal acidification. This study provides the first baseline estimates of how high-frequency pH, aragonite saturation state (Ωaragonite), and pCO2 dynamics are altered by local production, respiration, and exchange with the atmosphere in an estuarine habitat. Our study utilized a combination of high-resolution observations, mechanistic modeling, multiple techniques for estimating anthropogenic carbon loading into the system, and hindcasting/forecasting models to determine the impacts of altered local biological rates with changing atmospheric exchange rates in a seagrass habitat in Puget Sound, WA, USA. We find that as anthropogenic carbon continues to increase in the atmosphere and enters coastal waters, the carbonate system of an estuarine seagrass bed becomes less able to buffer natural sources of CO2 variance, causing non-linear amplification of naturally extreme events. Net community metabolism of the seagrass bed is found to currently increase the incidence of both harmful and favorable bio-calcifying conditions, while ultimately reducing organismal exposure to harmful conditions in future high-CO2 scenarios. This presentation contributes to SSWR 4.02B.
Description:
Rising atmospheric CO2 due to anthropogenic emissions alters local atmospheric gas exchange rates in estuaries, causing alterations of the seawater carbonate system and reductions in pH broadly described as coastal acidification. These changes in marine chemistry have been demonstrated to negatively affect a variety of coastal and estuarine organisms. The naturally dynamic carbonate chemistry of estuaries driven by biological activity, hydrodynamic processes, and intensive biogeochemical cycling has led to uncertainty regarding the role of rising atmospheric CO2 as a driver in these systems, and the suggestion that altered atmospheric exchange may be relatively unimportant to estuarine biogeochemistry. For this study, we estimated how rising atmospheric CO2 from 1765 through 2100 interacts with the observed local carbonate chemistry dynamics of a seagrass bed, and calculated how pHT, pCO2, and Ωaragonite respond. We find that as anthropogenic carbon continues to increase in the atmosphere and interact with local estuarine biogeochemical processes, the carbonate system of an estuarine seagrass bed becomes less able to buffer natural sources of CO2 variance, causing non-linear amplification of naturally extreme events. Model results indicate net community metabolism within the seagrass bed increases the exceedance of carbonate chemistry thresholds for both positive and negative effects on resident organisms in the present and near-future, while ultimately reducing organismal exposure to harmful conditions in a future, high CO2 world. Despite increasingly variable and extreme carbonate weather in these productive habitats with increasing anthropogenic CO2, net autotrophic habitats will potentially act as chemical refugia when compared with more heterotrophic habitats at future higher atmospheric CO2 levels.