Puget Sound nutrient pollution studies

We use a peer-reviewed, state-of-the-science computer modeling tool called the Salish Sea Model to conduct nutrient pollution studies. These studies help us understand how, where, and when nutrients contribute to low oxygen levels in Puget Sound, so that we can develop solutions for improving water quality in Puget Sound. Excessive nutrients in rivers and from point sources flowing into the Sound — such as municipal wastewater treatment plants — deplete dissolved oxygen below the water quality standards.

You may directly download model outputs and data and view all Salish Sea Model publications


Salish Sea image with ferry crossing channel. Mount Baker view in the background.

New results: Optimization scenarios tech memo

Technical Memorandum: Puget Sound Nutrient Source Reduction Project Phase II - Optimization Scenarios (Year 1) is an interim analysis on the lastest Salish Sea modeling results conducted in 2020 – 2021. The Tech Memo includes results from a series of scenarios we evaluated, including predicted changes to dissolved oxygen levels due to:

  • Watershed nutrient reductions by region
  • Wastewater treatment plant (WWTP) reductions by region
  • Annual vs. seasonal treatment at WWTPs
  • Future population growth projections
  • Combinations of watershed and WWTP reductions

Our blog post "Nutrient pollution modeling shows different futures for Puget Sound" offers a high-level overview of this study.  Tech Memo appendices are posted on the Nutrient Forum webpage.

Salish Sea Modeling webmap

The Puget Sound Nutrient Source Reduction Project: Salish Sea Model results interactive webmap is an interactive map where you may view the latest modeling results included in the 2021 Tech Memo. Watch this tutorial video on how to navigate the webmap.

Bounding Scenarios Report (2019)

Puget Sound Nutrient Source Reduction Project. Volume 1: Model Updates and Bounding Scenarios, or the Bounding Scenerios report, evaluated changes to dissolved oxygen levels when modeling reductions in nitrogen and carbon at municipal wasterwater treatment plants. 

The Salish Sea Model study confirmed that human sources of nutrients have a significant impact on dissolved oxygen in Puget Sound embayments. This assessment concluded that reducing nutrient pollution at municipal wastewater treatment plants would provide significant progress toward meeting dissolved oxygen water quality standards in the sound.

Future modeling

It is clear from our modeling studies that it will take a combination of nutrient reductions from wastewater treatment plants and other sources of nutrient pollution in watersheds to meet marine water quality standards. We will continue evaluating nutrient reduction scenarios in 2021 – 2022. Results of this modeling will inform the Puget Sound Nutrient Reduction Plan.

Subscribe to the Puget Sound Nutrient Forum listserv to stay informed on future modeling efforts and reports.