The Department of Ecology and Pacific Northwest National Laboratory evaluated future dissolved oxygen scenarios within the Salish Sea using a circulation and water quality model of Puget Sound, the Strait of Georgia, and the Strait of Juan de Fuca. A recently published report summarizes relative contributions of human nutrient sources, the Pacific Ocean, and climate factors on dissolved oxygen both now and through 2070. Human nitrogen contributions from the U.S. and Canada to the Salish Sea have the greatest impacts on dissolved oxygen in portions of South and Central Puget Sound. Marine point sources cause greater impacts on oxygen than human influences on river inflows now and into the future. Most of the Salish Sea reflects a relatively low impact from human sources, although that will increase as loads increase. The Pacific Ocean strongly influences dissolved oxygen concentrations under both current and future conditions. If 50-year declining trends in North Pacific Ocean dissolved oxygen continue, Salish Sea dissolved oxygen would decline far more than from human nutrient loads. Climate change will alter the timing of freshwater flow reaching the Salish Sea, as provided by the University of Washington Climate Impacts Group. This would alter estuarine circulation patterns, potentially worsening impacts in some regions but lessening others. Future air temperature increases would further decrease dissolved oxygen, particularly in shallow inlets. This is the first assessment of how Salish Sea dissolved oxygen concentrations respond to population increases, ocean conditions, and climate change. Additional analyses are needed to link sediment-water interactions and increase scientific certainty
