Marine Water Quality

Marine water quality refers to aspects of water such as temperature, salinity, oxygen, nutrient levels, algae biomass, and pH. In much of Puget Sound, marine water quality is affected by many different factors including weather, climate and circulation patterns, offshore ocean conditions, inflow from rivers and streams, discharges from wastewater treatment plants and industries, erosion and stormwater runoff, ground water, and pollution. The Marine Water Quality Vital Sign gives us context for changes seen throughout the Puget Sound ecosystem: it tells us about the impacts of global and local change and human-caused stresses on Puget Sound marine waters. Marine water quality affects the food web, from the smallest invertebrates to the largest whales and humans.


Key Vital Sign Messages

 Tool that measures temperature, depth and other water properties. Photo J Newton

Although Puget Sound may look beautiful from the surface, marine water quality has changed in many ways. Monitoring programs document marine water quality and how Puget Sound changes over time. One challenge is gathering enough data – especially historical data – to truly understand what the ecosystem used to be like compared to now. Shifts over time in the expectations for a healthy ecosystem is referred to as “shifting baselines”. By establishing scientifically sound baselines for water quality parameters, researchers can detect changes and predict what Puget Sound will be like for future generations.

Many unknowns exist regarding Puget Sound’s future. Climate change is impacting the water cycle throughout Puget Sound, altering the seasonality and timing of key chemical, physical, and biological processes. Climate is a huge driver of marine water quality and the marine food web. As climate changes, so does the way plants and animals live in Puget Sound and how humans use Puget Sound’s resources.

  • As the climate changes, so too does temperature and salinity. In 2019, Puget Sound waters were warmer and saltier than average – although not as warm as during the year of the “blob” of warm water from the NE Pacific Ocean. Abnormally warm and salty waters impact the Puget Sound food web; however, predicting effects on species is difficult. Warmer waters can be inhospitable to some animals (like salmon) but welcoming to other animals (like anchovy). And impacts can be complicated: warmer waters may support more abundant zooplankton populations or different types of zooplankton, which can alter food availability for fishes like Chinook salmon and Pacific herring.
  • The structure of the water column affects water quality and the food web depending on season and location. Stratification is when density layers form within the water column, with less dense (warmer, fresher) water layers sitting above denser (cooler, saltier) water layers. Turbulence caused by winds or upwelling and downwelling forces can mix these layers. In 2019, Puget Sound waters were generally more mixed than previous years despite a gradual 20-year increase in stratification. More mixing can allow nutrients to mix throughout the water column but can also inhibit phytoplankton blooms from forming, producing less food to fuel the food web.
  • Dissolved oxygen levels in many parts of Puget Sound were lower on average in 2019 compared to the baseline (1999–2008) conditions, continuing a six-year declining oxygen trend. The trend corresponds with anomalously warm waters (warmer water holds less oxygen). In contrast to this broader trend, certain areas (Central Basin, Quartermaster Harbor, and Bellingham Bay) reported normal to above normal oxygen – likely due to short-term effects of phytoplankton blooms or water circulation. Low oxygen waters may stress or kill fish, shellfish, and other underwater animals. In 2019, hypoxia (low oxygen) persisted from July to November in South Hood Canal, where low-oxygen areas are common at certain times of the year; luckily, no fish kills were reported.
  • Ocean acidification refers to the chemical changes that occur when the ocean’s surface absorbs excess carbon dioxide in the atmosphere. The absorption results in more acidic waters and corrosive conditions for calcifying organisms like shellfish. More acidic waters can also affect metabolic responses that control animal growth and reproduction. Ocean acidification is a continuing problem particularly in Hood Canal and the Washington coast, where carbon dioxide concentrations are higher than global averages.
  • Nitrogen is a nutrient that marine plants and animals need to grow. However, too much nitrogen can fuel algae blooms that decompose and deplete oxygen from the water. Nitrate (a form of nitrogen) in Puget Sound surface water peaked in the mid-2000s and has decreased since then. The frequency of intense phytoplankton blooms has declined while water clarity has increased since 1999. Trend patterns in nitrate, blooms and water clarity may be related to changing nutrient ratios due to changes in nutrient supply to the marine environment via weathering of feeder bluffs, loss of beach nourishment due to shoreline armoring, or changes in river flows.
  • While phytoplankton blooms varied regionally, overall abundance was generally higher in 2019. Some blooms caused numerous closures of commercial and recreational shellfish harvesters to prevent cases of paralytic, amnesiac, and diarrhetic shellfish poisoning. Fortunately, no illnesses were reported from these harmful algal blooms. However, the bacterial pathogen Vibrio parahaemolyticus caused 125 cases of illness due to contaminated recreational and commercial oyster harvests. One Puget Sound growing area (Hammersley Inlet) was closed to protect public health from Vibrio.
  • Microplastics are present in Puget Sound. However, the extent and impacts on marine life are not well known. Analysis of sediments across Puget Sound reveals the presence of microplastics in all samples collected except one since 2014.

For more information about marine water quality and observations, please see the Marine Waters 2019 Overview. For recent preliminary data and observations, please visit our Marine Condition Update website. For a list of monitoring programs related to marine water quality in Puget Sound, please visit our webpage.

Strategies, Actions, and Effectiveness

Contributing Partners

PSEMP Marine Waters Work Group (coordinator is Iris Kemp)
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