Ecological (biogeochemical) Predictions for the Inner Salish Sea given Warming Temperatures and Increasing Nutrient and Carbon Levels in Upwelled Ocean Waters

Prior biogeochemical assessments of the Salish Sea estuarine system have shown that the Pacific Northwest coastal waters will be subjected to changing ocean states which will be considerably warmer (approx.+2.63 deg.C), lower in dissolved oxygen (approx.-1.73 mg/L), more acidic (approx. -0.36 pH units), and will in general carry higher concentrations of nutrients and dissolved inorganic carbon in year 2095 (based on one realization of IPCC future high emissions scenario RCP8.5). These altered future projected conditions from a global climate model in the upwelled shelf waters were shown to propagate into the inner Salish Sea and impact biogeochemistry, resulting in higher predicted algal biomass and a potential species shift from diatoms towards dinoflagellates, and increased regions of hypoxia and acidification. However, these predictions were limited due to simplifications associated with predation, light availability, and submerged aquatic vegetation (SAV) terms in the original Salish Sea model. To improve ecological response predictions, micro- and meso-zooplankton kinetics were incorporated along with SAV which competes with phytoplankton for available nutrients in the photic zone. Seasonal controls on phytoplankton growth were improved with a better prediction of turbidity and light availability and with explicit simulation of zooplankton growth and predation. We applied the model in a scenario testing mode to re-evaluate future ecological response related to species shift and examined nutrient and carbon pools including the influence of zooplankton production, metabolism and predation-pray interactions. Similarly, the beneficial role of SAV under future nutrient and carbon rich environment was examined with respect to potential for improvements to DO and pH levels. The possibility of increased SAV growth as a mitigation measure against ocean acidification and the feasibility of using strategies such as restoration of eelgrass or tidal marshes and nutrient load reduction as mitigation measures were examined for the Salish Sea waters.