water quality in the Puget Sound

Puget Sound covers roughly 1,000 square miles (Puget Sound Institute 2015) in surface area and is the largest estuary in the United States by volume. It’s basin, or drainage area encompasses approximately 13,700 square miles (USGS 2000). It is fed by more than 2,800 rivers and streams, many of which begin in the Cascade or Olympic mountains and flow through forests, farmlands, and urban areas before reaching the Sound itself (Puget Sound Institute). The Puget Sound is home to several salmon species which act as a food source for other wildlife, such as southern resident orcas, and are of economic and cultural importance to human residents of Puget Sound.

The number of people calling the Puget Sound area home increased 15.6% from 2000 to 2010 (WNDR 2015) and is now home to 4.2 million people. The population is projected to reach approximately 5.8 million people by 2050 thanks in part to a projected addition of 1.1 million jobs to the region’s economy (Puget Sound Regional Council 2018). The Seattle metropolitan area is the 11 largest regional economy in the US with a GDP of $392 billion in 2018 (Federal Reserve Bank of St. Louis 2020). 

As more people come to live in the Puget Sound basin, cities expand and dramatically alter the physical characteristics and hydrology of local watersheds. This process of watershed urbanization is characterized by, among other things, a loss of native vegetation and soil compaction. Loss of native vegetation, primarily conifer forests in the Pacific Northwest, leads to a loss of water storage due to a reduction in canopy interception of precipitation. Soil compaction reduces infiltration rates significantly and covering soil with roads, rooftops, and parking lots reduces infiltration rates to zero. The result is a dramatic increase in stormwater runoff. For example, a conventional parking lot generates 16x more stormwater runoff than a natural meadow (Schueler 1994). All of this extra runoff has a dramatic impact on the hydrology (i.e. stream flow magnitude and timing) of a stream or river. Alteration of hydrology can significantly degrade instream habitat (May et al. 1997) which has negative impacts on biota such as salmon.

As the human population within the region increases, so too does the percentage of impervious cover. A study in 2010 estimated that impervious cover within the Puget Sound basin increased from 3.7% to 4.1% just between the years of 1996 to 2006 (Parametrix 2010). Research indicates that measurable and often irreversible ecosystem damage occurs once impervious cover reaches 10% within a watershed (Booth and Reinelt 1993 – cited many locations but can’t seem to find original). 

Urban stormwater is the leading source of nonpoint pollution to urban waters (Scholz and McIntyre 2016). The primary nonpoint source pollutants in stormwater include nutrients, sediment, bacteria, and toxic chemicals (Ecology 2011).  Studies have shown that Seattle roadways contribute hundreds of manmade chemicals to Seattle-area streams (From Chow et al. 2019). In 2011 the Washington State Department of Ecology and King County conducted an assessment of 17 toxic chemical groups. They found that surface runoff was the primary pathway for most toxics entering Puget Sound and that commercial and industrial areas released the highest concentrations of toxics of the four assessed land uses (commercial/industrial, residential, agricultural, and forest (Ecology and King County 2011). 

This leads us to the question, what is the health of Puget Sound and is it getting better or worse? Overall, data suggest that Puget Sound health is declining or at best, not improving. The Puget Sound Partnership (PSP), using data from partners such as the Washington Department of Fish and Wildlife and the Department of Ecology, measures ecosystem health and tracks progress towards recovery goals in Puget Sound via a list of 50 indicators. Marine water quality index and freshwater quality index are two of these indicators. Based on data collected over the previous 20 years, marine water quality is declining and freshwater quality is remaining the same and is not improving (Puget Sound Info 2019).

The next question is, why should we care? The health of Puget Sound effects it’s human residents directly and indirectly. Puget Sound is home to valuable commercial fishing and shellfish operations. For example, Puget Sound commercial shellfish operations are valued at over $100 million annually (Dethier 2006 – From Encyclopedia of PS Fact Book). Furthermore, recreational shellfish harvesting accounts for at least $5.4 million annually (2011 Washington Shellfish Initiative). Due to poor water quality in the Puget Sound, 15% of classified commercial and recreational shellfish beds are closed to harvest. One of the primary sources of pollutants affecting these shellfish beds is combined sewer overflows due to high runoff following rain events (Vital Signs).

Salmon fisheries are also valuable to the Puget Sound ecosystem and to its tribal and nontribal populations. Salmon constitute a large proportion of commercial fish catch in the Puget Sound. In addition, they are of cultural significance to the native tribes throughout the region. Of particular importance is the Chinook salmon. Being the largest the salmon species it has the ability to contribute the largest amount of biomass to local ecosystems (EPA). Furthermore, chinook represent a significant proportion of southern resident orca’s diets, roughly 70% (Ford et al. 2009). Data suggests that Chinook numbers are not improving in Puget Sound and most populations remain far below recovery targets set by the National Fisheries Marine Service (Vital Signs).

Of particular concern for salmon in highly urbanized areas of Puget Sound are toxins found in stormwater. For at least the past two decades, urban streams in central Puget Sound have experienced 60%-100% salmon spawning mortality and it appears that pollutants in urban stormwater are a major reason behind this (Scholz et al. 2011). A study examining the impacts of Seattle highway runoff found that 100% of adult coho salmon exposed to Seattle highway stormwater runoff displayed spawner mortality syndrome. This rate was reduced to 0% after the stormwater was filtered through a soil bioretention system (Spromberg et al. 2016). Another study found that juvenile coho exposed to polluted highway runoff displayed mortality syndrome and did not recover when transferred to clean water. This suggests that exposure to a single stormwater runoff event could have lethal effects on juvenile salmon (Chow et al. 2019).

Notes

• Human sources of nutrients cause a reduction greater than 0.2 mg/L of dissolved oxygen, and therefore in violation of Washington state water quality criteria, at several embayments in Puget Sound. At several points in Puget sound, these human-caused reductions in dissolved oxygen persist for three months or more. (https://vitalsigns.pugetsoundinfo.wa.gov/VitalSignIndicator/Detail/29)

• PCB concentrations in adult resident Chinook salmon exceeded DOH screening values in all marine areas sampled in Puget Sound (https://vitalsigns.pugetsoundinfo.wa.gov/VitalSignIndicator/Detail/47).

• PCB concentrations in juvenile Chinook salmon exceeded 2020 targets in 4 out of 11 sampling sites. The four sites exceeding the target were highly urbanized and included the Duwamish, Hylebos/Puyallup, and Snohomish river/estuary systems and Lake Washington. The PCB concentrations are high enough in concentration to likely to reduce survival among juvenile salmon. (https://vitalsigns.pugetsoundinfo.wa.gov/VitalSignIndicator/Detail/49)

• Washington State water quality criteria: https://apps.leg.wa.gov/WAC/default.aspx?cite=173-201A-210&pdf=true

• Sources of bacteria contamination include stormwater, failing septic systems, boat waste discharge, pet waste, livestock waste, sewage overflows, wastewater treatment plant malfunctions, and wildlife.  (https://ecology.wa.gov/Water-Shorelines/Puget-Sound/Issues-problems/Bacteria)

Puget Sound INITIATIVE

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Jacobson, M., Wildish, J. 2020. Water Quality in the Puget Sound. Earth Economics, Tacoma, WA.

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