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Short-term pain for long-term gain: seagrass communities increase short-term extremes and long-term offset of CO2 under future ocean acidification
Citation:
Pacella, S., C. Brown, G. Waldbusser, R. Labiosa, AND B. Hales. Short-term pain for long-term gain: seagrass communities increase short-term extremes and long-term offset of CO2 under future ocean acidification. 2017 Coastal and Estuarine Research Federation Conference, Providence, Rhode Island, November 05 - 09, 2017.
Impact/Purpose:
The impacts of ocean acidification in nearshore estuarine environments remain poorly characterized, despite these areas being some of the most ecologically important habitats in the global ocean. Here, we quantify how rising atmospheric CO2 from 1765 to 2100 alters high-frequency carbonate chemistry dynamics in an estuarine seagrass bed. We find that increasing anthropogenic carbon reduces the ability of the system to buffer natural extremes in CO2. This reduced buffering capacity leads to preferential amplification of naturally extreme low pH and high pCO2(s.w.) events above changes in average conditions, and also outpace rates published for atmospheric and open-ocean CO2 change. Seagrass community metabolism drives these short-term extreme events, yet ultimately reduces organismal exposure to harmful conditions in future high-CO2 scenarios. Results of this study highlight challenges for water quality management related to ocean acidification.
Description:
The impacts of ocean acidification in nearshore estuarine environments remain poorly characterized, despite these areas being some of the most ecologically, economically, and culturally important habitats in the global ocean. Here, we quantify how rising atmospheric CO2 from 1765 to 2100 alters high-frequency carbonate chemistry dynamics in an estuarine seagrass bed. We first reconstructed the full carbonate system of an estuarine seagrass bed for a summer period of 2.5 months utilizing a combination of time-series observations and mechanistic modeling, and quantified the roles of community metabolism, mixing, and gas exchange in the observed dynamics. Utilizing this time series of carbonate chemistry, we then simulated the anthropogenic CO2 burden in the habitat through equilibration with atmospheric CO2 concentrations from 1765-2100. The addition of anthropogenic CO2 alters the thermodynamic buffer factors (e.g. the Revelle factor) of the carbonate system, decreasing the carbonate system’s ability to buffer natural variability in the seagrass habitat. As a result, the most harmful carbonate system indices for many estuarine organisms (minimum pHT, minimum Ωarag, and maximum pCO2(s.w.)) change up to 1.8x, 2.3x, and 1.5x more rapidly than the medians for each parameter, respectively. In this system, the relative benefits of the seagrass bed in locally mitigating ocean acidification 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. We highlight how the non-linear responses of coastal carbonate parameters to ocean acidification are relevant for water quality management.