Marine water quality long-term trends

Since 1999, we have gathered monthly water quality data at 37 stations in Puget Sound, Grays Harbor, and Willapa Bay to determine long-term trends in nutrients, algal biomass, and dissolved oxygen. We monitor these parameters, plus a suite of additional physical, chemical, and bio-optical variables, to determine the status and trends of water quality in the context of climatic and human pressures.

Unusually warm sea conditions, drought, and an early snowmelt followed by a wet summer, created unique results in our 2015 long-term monitoring report on marine water quality.

In our 2015 long-term marine monitoring report, we found:

  • Nutrients are increasing.
  • Oxygen is improving.
  • Phytoplankton is declining.
  • Water is clearer.

The long-term data collected allows us to evaluate current data against historic baselines. This allows us to report if conditions are normal, outside of statistical parameters, or if there are new record highs or lows.

Physical oceanographic conditions

A summary of Puget Sound's physical conditions for 2015

CTD sensors check the conductivity, temperature, and density of saltwater.
  • New maximum water temperatures set records everywhere in Puget Sound, connected to a large-scale Pacific Ocean temperature anomaly, informally known as “the blob,” a mass of unusually warm water.
  • Salinity and density stratification fluctuated seasonally between:
    • Less saline and strongly stratified conditions in spring.
    • Saltier and more mixed conditions in summer.
    • Re-establishment of less saline and strongly stratified conditions at the end of the year, caused by record rainfall.
  • Drought conditions in 2015 allowed Puget Sound to vertically mix. This buffered the negative effect of warmer water temperatures and higher residence time of water in Puget Sound.

Conditions for plankton blooms

The seasonal patterns of ammonium and chlorophyll in relation to Noctiluca algae blooms suggests an important role of Noctiluca in material cycling within central Puget Sound in early summer. Peaks in ammonium and decreased chlorophyll concentrations appeared to coincide with growth of Noctiluca, which grazes on phytoplankton.

Water temperature between 10 and 13° C coincided with Noctiluca blooms. In 2015, water temperatures over 15 °C, which is conducive to harmful algal bloom forming species, persisted longer and covered a larger geographical region of central sound.

Nutrient patterns

The long-term trend of increasing nitrate concentrations and decreasing chlorophyll seems to have ceased. There is a negative and persistent relation between nutrient and phytoplankton biomass over the past 16 years. This illustrates the importance of biologic controls of dissolved inorganic nutrient pools. These dissolved inorganic nutrients need to be analyzed for trends. The seasonal cycle of phytoplankton in 2015 occurred one month early, whereas ammonium levels were very high and appeared one month late.

Dissolved oxygen levels

The 2015 dissolved oxygen (DO) deficit for Puget Sound was higher overall, similar to 2013 and 2006 measurements. Lower than normal DO was observed in the first part of the year, raising concerns for water quality issues later in the year. Historical minimums in river flows during the 2015 summer drought, coupled with improved conditions for vertical mixing, allowed DO to recover to normal levels in summer.