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Saving Puget Sound

Puget Sound/Salish Sea Model

The Department of Ecology (Ecology) is using a water quality model to evaluate the effects of current and potential future nutrient loads on dissolved oxygen levels in Salish Sea. The Puget Sound/Salish Sea model, a computerized prediction tool, helps us understand:

  • Are human sources of nutrients in and around the Salish Sea significantly impacting water quality?
  • How much do we need to reduce human sources of nutrients to protect water quality in the Salish Sea?

These model findings will help decision-makers use resources wisely and guide where additional study or action is necessary.

Project Status

Ecology, in collaboration with Pacific Northwest National Laboratory, completed the report: Dissolved Oxygen Assessment for Puget Sound and the Straits: Impacts of Current and Future Human Nitrogen Sources and Climate Change through 2070.

The study found human nutrient sources impact South and Central Puget Sound more than other areas of the Salish Sea. The Pacific Ocean has the largest overall influence. More work is needed to improve our computer prediction models over the next few years. We will continue to coordinate with cities, counties, tribes, and other stakeholders through the Advisory Committee. Next steps include modifying sediment-water interactions.

Model Results

Additional information on the Salish Sea dissolved oxygen model can be found on a partner web page developed by Pacific Northwest National Laboratory. These include animations of oxygen and chlorophyll.

Summary of the water quality model

Ecology and Pacific Northwest National Laboratory have developed circulation and water quality models of the Salish Sea. This includes all of Puget Sound, the Strait of Juan de Fuca, and the Strait of Georgia. The purpose is to evaluate relative impacts on dissolved oxygen from human nutrient loads, Pacific Ocean conditions, and climate change.

The model includes of 64 rivers and 99 wastewater treatment plants in the U.S. and Canada. Early publications documented the approach, circulation model calibration, nutrient inputs, and water quality model calibration. The recent scenarios report published best available information on current and future conditions in the Salish Sea.

Human nitrogen contributions from the U.S. and Canada to the Salish Sea have the greatest impacts on oxygen in portions of South and Central Puget Sound. Both will increase with population growth and land use change. Most of the Salish Sea reflects a relatively low impact from human sources of nitrogen currently. Higher nitrogen inputs would result in decreasing oxygen.

The Pacific Ocean strongly influences oxygen concentrations under both current and future conditions. If 50-year declining trends in North Pacific Ocean oxygen concentrations continue, Salish Sea oxygen would decline far more than from human nutrient loads. However, future ocean conditions are highly uncertain.

Climate change will alter the timing of freshwater flows, which would worsen oxygen impacts in some area but lessen others. Future air temperature increases would further decrease oxygen, particularly in shallow inlets.

Related information

Advisory Committees

For more information, please contact:

Dustin Bilhimer
Water Quality Program
Washington State Dept. of Ecology
P.O. Box 47600
Olympia, WA 98504-7600
Phone: 360-407-7143
E-mail: Dustin.Bilhimer@ecy.wa.gov


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Last updated August 2016


South Puget Sound Dissolved Oxygen Study

Nitrogen in Puget Sound