Puget Sound Marine Sediment Indicators

Scientists have developed several ecological indicators to track the health of the Puget Sound ecosystem and how it changes over time. Sediment health is assessed with a Sediment Chemistry Index, a Sediment Toxicity Index, and a Sediment Benthic Index of sediment-dwelling invertebrate community structure. A Sediment Quality Triad Index combines these separate indicators into a single assessment of sediment quality. The Sediment Chemistry Index and Sediment Quality Triad Index were adopted by the Puget Sound Partnership as Vital Signs Dashboard Indicators.

An explanation of each sediment quality index is given below.

Sediment Chemistry Index for Puget Sound

Adopted by the Puget Sound Partnership as part of the Dashboard of Vital Signs.  

The Sediment Chemistry Index identifies sediments likely to have adverse effects on sediment-dwelling invertebrates (benthos) as a result of exposure to complex mixtures of potentially toxic chemicals accumulated in the sediments. The  values are based on the ratio of chemical concentrations to their respective Washington State Sediment Quality. Standards values and are scaled from 0 (poorest quality) to 100 (highest quality). (See summary of derivation of Sediment Chemistry Index values.)

Critical Sediment Chemistry Index threshold values were selected for Puget Sound based on relationships between the chemistry, toxicity, and benthos data collected throughout the Sound. Four ranges and categories of relative sediment quality (minimum to maximum exposure to toxic chemicals) were created (Long et al., 2013). The value of >93.3 was adopted by the Puget Sound Partnership as one of several “target” values to be achieved by the year 2020 for sediments in routinely monitored Puget Sound regions and bays. (See Sediment Quality Vital Sign target values.) At this target level, benthos should have minimal exposure to toxic chemicals in sediments.

Sediment Chemistry Index for Puget Sound: 

Compared Across Regions
Compared Across Urban Embayments
Sediment Toxicity Index for Puget Sound
The Sediment Toxicity Index is a measure of relative degree of toxicity of each sampling station. The Index combines the outcomes of two laboratory toxicity tests:
  • Percent survival of amphipods in test sediments.
  • Percent successful fertilization of sea urchin gametes in test sediment porewater.

The value is based on the results from the toxicity test with the lowest control-adjusted result (i.e., lowest survival or fertilization success) and degree of statistical significance. Sediment Toxicity Index values range from 0 (poorest quality to 100 (highest quality). Critical values have been set for both tests, and were used to create four ranges and categories of relative sediment toxicity (non-toxic to highly toxic). (See derivation of  values.)

 A suggested target for samples collected from Puget Sound would be to fall within the “non-toxic” category, in which mean sample test results are not statistically significantly lower than the mean control tests results.

Sediment Toxicity Index for Puget Sound:
Compared Across Regions
Compared Across Urban Embayments
Sediment Benthic Index for Puget Sound  
The Sediment Benthic Index is used to classify the relative condition of the sediment-dwelling invertebrate communities (i.e., benthos) as either “adversely affected” or “unaffected” by natural or human-made stressors. The current/interim method of classifying the benthos examines the following:
  • Values of 9 calculated benthic measures (total abundance; taxa richness; evenness; species dominance; and abundance of annelids, arthropods, molluscs, echinoderms, and miscellaneous taxa).
  • Presence, absence, and abundance of stress-sensitive and -tolerant species.
  • Best Professional Judgment (includes consideration of known habitat characteristics, e.g., grain size, TOC, depth, salinity).

The current binary designations of “adversely affected” and “unaffected” have been assigned interim values of 50 and 100, respectively, until a more refined benthic index scale (under development) is adopted. (See derivation of  values.)

 
Numerical Benthic Index for Puget Sound Under Development
Ecology is collaborating with the Southern California Coastal Water Research Project (SCCWRP) to develop a numerical benthic health index for Puget Soundon a scale of  0 (poorest quality) to 100 (highest quality).  The new Sediment Benthic Index will be used to separate the benthic infaunal community data into four categories of relative condition of the benthos, including:
  • Reference
  • Low Disturbance
  • Moderate Disturbance
  • High Disturbance
The suggested appropriate target value for Puget Sound benthos will be based on a determination of  "reference" condition.

 Sediment Quality Triad Index for Puget Sound

Adopted by the Puget Sound Partnership as part of the Dashboard of Vital Signs.
The Sediment Quality Triad Index is a measure of the relative quality of the sediments based on a Multiple Lines of Evidence (MLOE) approach developed by scientists (Bay and Weisberg, 2012) at the Southern California Coastal Water Research Project (SCCWRP). Following MLOE, all possible combinations of the 4 chemistry, 4 toxicity, and 2 interim benthos categories are generated to describe each sample. The 32 combinations are ranked, placed on a scale of 0 (poorest quality) to 100 (highest quality), and grouped into 6 categories of relative quality, from “unimpacted” to “clearly impacted” and “inconclusive.”  (See derivation of values.)
Sediment Quality Triad Index Reporting Levels
 
Puget Sound-Wide 8 Monitoring Regions 6 Urban Bays
Marine Sediment Quality for the greater Puget Sound is assessed every ten years. PDF summaries may be downloaded below:

Regional Sediment Quality

Urban Bays Sediment Quality
San Juan Islands
Eastern Strait of Juan de Fuca
Admiralty Inlet
Strait of Georgia
Whidbey Basin
Central Sound
Hood Canal
South Sound
Elliott Bay and the Lower Duwamish Waterway
Commencement Bay
Sinclair and Dyes Inlet and the adjoining Bainbridge Basin
Bellingham Bay
Budd Inlet
Everett Harbor and the Snohomish River Delta