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Puget Sound Georgia Basin Model

Ocean Acidification and pH

Background and motivation

Biogeochemical processes such as algal growth and die-off affect total inorganic carbon in the water column and therefore affect pH. We know that shallow sub-basins in Puget Sound and Georgia Basin regions of Salish Sea are highly productive, which results in almost complete depletion of nutrients during the spring and summer algae blooms. Discharge of nutrient pollutants into the Salish Sea during these periods could lead to eutrophic conditions. High levels of algae during the daytime lead to super-saturated dissolved oxygen (DO) levels. The same algae during the nighttime produce copious amounts of carbon dioxide (CO2) through respiration resulting in reduced pH. At the conclusion of the spring and summer blooms, algae die, decay, and settle to sediments, leading to conditions suitable for hypoxia. The decaying algae also release large amounts of inorganic carbon back to the water column. Data from sub-basins of Puget Sound show sharp drops in pH correlated to nighttime respiration. This problem is exacerbated by ocean acidification and upwelling. While we cannot stop the natural events, we can certainly modify our fisheries and water-quality management practices to better plan for these events and minimize their potential impacts. Monitoring and modeling can help forecast conditions and manage and adapt our activities to minimize the adverse effects.

Schematic diagram of the carbon cycle in the coastal and estuarine system.

Key physical and biogeochemical processes and pathways including human contributions in the coastal zone.

The Blue Ribbon Panel of scientists, tribes, and shellfish managers appointed by Governor Christine Gregoire recommended future research, monitoring, and actions to understand, prevent or mitigate, and adapt to the acidification of Washington State marine waters. The panel recommended efforts to quantify how much regional human sources (water nutrients and air emissions) exacerbate the effects of the upwelled Pacific Ocean water and global atmospheric CO2 on the acidification of marine waters. PNNL and Ecology have developed a planning document that summarizes the initial approach recommended to simulate the impacts of regional human sources on acidification. Proposed modeling will depend on funding from the Washington State Legislature.

Salish Sea Model

Ocean Acidification