Reducing nutrients in Puget Sound

Excessive levels of nutrients from human sources are changing Puget Sound's water quality, adversely affecting the nation's second largest marine estuary. These excess nutrients, such as nitrogen and carbon, can lead to low dissolved oxygen, which impacts the health and resilience of aquatic life. Monitoring data has identified many places throughout Puget Sound that are impaired for dissolved oxygen. 

The Puget Sound Nutrient Source Reduction Project is a collaborative effort with communities and Puget Sound stakeholders, to address human sources of nutrients. This work focuses using the latest science to find the right solutions for regional investments to control nutrients from point and non-point sources. These investments will help improve Puget Sound water quality, support salmon and orca recovery, and increase resiliency to climate impacts. 

Puget Sound Nutrient Forum 

The Puget Sound Nutrient Forum is a public advisory group created to discuss, learn, and provide input on how to reduce human sources of nutrients entering Puget Sound. Participants include representatives from wastewater treatment plants, municipalities and counties, tribes, environmental groups, industry groups, watershed and salmon restoration organizations, state and federal government agencies, and members of the public.

We held a series of meetings in 2018 discussing what we and the rest of the scientific community know about the effects of nutrient over-enrichment and trends in Puget Sound. 

Previous meeting materials are available to download.

Visit our meeting page to learn more about our 2019 meetings.  

Please register for our email listserv to receive information updates about the Forum meetings.

Nutrient over-enrichment

Discharges of nutrients to Puget Sound — and the rivers that drain to it — act like fertilizer and cause too much plant and algae growth for a healthy, resilient marine ecosystem. When these plants and algae die, their decomposition uses oxygen that marine animals need to survive.

The nutrients come from both natural processes — such as ocean upwelling and aerial deposition — and human sources.

Humans can contribute excess nutrients through:

  • Wastewater treatment discharges.
  • Stormwater runoff.
  • Onsite sewage systems.
While global human activities also affect nutrients in the ocean and air, we still need to work on controlling local sources of nutrients.

Collaborating with state-of-the-art research

We are beginning a collaborative process that uses state-of-the-art computer modeling tools and water quality data to evaluate meaningful nutrient reduction options. The primary objective is to improve Puget Sound's water quality by reducing human sources of nutrients, and make it more resilient to negative effects from climate change and Washington's increasing population pressures over the next several decades.

Understanding the complexities of the Salish Sea

A map of the Salish Sea and Pacific Ocean from Canada, north of Vancouver Island, south to Oregon, including Puget Sound.  Map shows polygonal study sections for modeling the Salish Sea.

The Pacific Northwest National Laboratory (PNNL) developed the Salish Sea computer model in collaboration with our scientists and engineers. The effort was funded by the U.S. Environmental Protection Agency.

The model helps us evaluate the complex chemical, physical, and biological interactions that affect marine water quality including:

  • Water circulation
  • Incoming ocean conditions
  • Watershed inflow and quality
  • Regional climate data
  • Human sources of nutrients and other parameters of concern

As this is the Salish Sea Model, it includes sources from both Washington and British Columbia. Water quality is continually changing in response to these factors. These changes are both over time — on a daily, seasonal, and annual basis — and geographically — meaning effects will vary from southern parts to northern areas of Puget Sound.

We are conducting extended scoping throughout 2017 that will allow us to figure out how this project can fit with other Puget Sound restoration activities. In 2018 we will begin working collaboratively with stakeholders and partners in the region to develop meaningful and holistic solutions for nutrient reduction and water quality improvement. We can use the Salish Sea model to evaluate the benefits of a variety of nutrient reduction solutions.

Using over a decade of data

In addition to using modeling tools, we are also incorporating water quality studies and data that has been collected over more than a decade. 

Water quality monitoring is a cornerstone of understanding how Puget Sound is changing over time. Monitoring data is used to compare against model predictions to ensure that the model is accurate and reflects reality.

However, marine water quality data alone cannot identify:

  • The level of impacts from nutrient pollution.
  • The specific human sources of nutrients.
  • How nutrient pollution affects water quality in all areas of the Sound during all times of the year.
We can use the Salish Sea model to analyze and quantify nutrient impacts from multiple sources that are both nearby and farther away from observed problems. Together, these scientific tools are very powerful for helping us understand and take care of Puget Sound.

People are part of the problem

Picture of Seattle from the water

Recent modeling of 2006 water quality conditions in Puget Sound allows us to tease apart impacts of human nutrient sources from natural and ocean sources. 

Human sources of nutrients include (among others):

  • Treated sewage
  • Over-application of fertilizers that get into stormwater runoff
  • onsite sewage systems (OSS)
  • Poorly managed land use practices

Using the Salish Sea model to estimate conditions in 2006, we are finding that discharges of nutrients from human sources are leading to dissolved oxygen problems in many parts of Puget Sound for significant durations during the year. We will also model more recent years to understand the range of effects from different climate and seasonal patterns experienced during those years.

Our growing population strains the system

There are over 4.5 million people living in the Puget Sound region right now and the Washington Office of Financial Management estimates around 1.7 million more people will move to the region by 2040 (source document). That additional number of people means there could be more than a 40 percent increase of nutrients discharged to Puget Sound from humans over the next several decades.

In addition to increasing pressures from population growth, climate change will make conditions worse. Altered watershed hydrology during drought years will reduce Puget Sound circulation resulting in concentrating nutrients from humans in Puget Sound instead of flushing them out to the ocean. Increasing water temperatures will increase productivity rates of unwanted flagellates, bacteria, and jellyfish. It will also lower the total amount of dissolved oxygen in water that fish and other marine organisms need to survive.

Working with stakeholders throughout the region and using the Salish Sea model to evaluate nutrient reduction options will ensure that the path we take and the solutions we invest in will help us restore and protect Puget Sound.

Isn't the ocean the greatest source of nutrients to Puget Sound?
Are dissolved oxygen and ocean acidification issues in Puget Sound related?
Why are wastewater treatment plants a problem? Don't they treat water before it is discharged?
How much do rivers and watersheds contribute nutrient inputs to the Puget Sound?
Will the problem get worse over time if we do nothing?
Will this become a Total Maximum Daily Load (TMDL) water cleanup plan?