Reducing nutrients in Puget Sound

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

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

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.

People are part of the problem

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.