Carbonate Chemistry in the San Juan Channel: Characterization and Suggestions for Mitigation

Abstract

Recent attention has been given to the potential vulnerability of coastal zones to ocean acidification. Urban estuaries such as the Salish Sea are strongly influenced by human activities and could be particularly vulnerable to the added stress of ocean acidification. At the same time, very little is known about ocean acidification condition in urban estuaries. To begin to address this need, I sampled seawater and measured carbonate chemistry at two stations and four depths over seven sampling time points during the fall of 2011. pH was variable but in all samples was substantially lower than contemporary values in open-ocean settings. pCO2 was correspondingly high. Aragonite saturation state - a measure of the kinetics of calcium carbonate precipitation - was uniformly undersaturated. Compared to open oceanic values, the relatively wide range in variation of carbonate variables observed could be due to a diversity of influences in this estuarine area, including the intrusion of upwelled waters from the outer coast, local upwelling within the Salish Sea, discharge from rivers, and inputs from human activities other than fossil fuel combustion. This last class of stressors - those that result from regional human activities - can be managed as a transboundary pollution issue. I propose that a regulatory toolkit be developed for use by regulators in the U.S. and Canada to address transboundary pollution issues under existing agreements. The toolkit will allow regulators to ascertain the extent of point-source discharges that can add regional ocean acidification and to develop local mitigation strategies to reduce the negative impacts of OA in the Salish Sea.