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- Marine Water
- Indicator
- Sediment Chemistry Index
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No targets are currently set for this indicator.
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Sandra Weakland
- Contributing Partners
- Last Updated
- 08/07/2024 08:38:18
The Sediment Chemistry Index (SCI) combines data on the concentrations of selected chemicals for which state Sediment Quality Standards Chemical Criteria have been set into an overall index of chemical exposure. Sediment quality is a key indicator of a healthy ecosystem, and high-quality sediments support a diverse and important biological community.
The Sediment Chemistry Index ranges from 0 to 100, with higher index values indicating less exposure to chemicals and thus healthier sediments. Sediments sampled between 1997 and 2022 met or exceeded the SCI threshold value of 93.3 in greater Puget Sound (error bars represent the 95% confidence intervals). Sediments sampled between 1998 and 2023 met or exceeded the SCI threshold value of 93.3 in five of six Puget Sound urban bays.
Chemical contaminants are considered a key anthropogenic (human-caused) pressure on the Puget Sound ecosystem. They can be toxic to biota, including benthic (bottom-dwelling) invertebrates. Also, contaminants taken up in benthic tissues may bioaccumulate, that is, be concentrated as they move up the food web.
Tracking the SCI gives an indication of how concentrations of selected chemicals in marine sediments change over time, primarily in response to anthropogenic input, such as stormwater runoff and direct discharge, as well as cleanup activities and passive burial as cleaner sediments settle over older, and sometimes more contaminated, sediments.
- The Sediment Chemistry Index (SCI) can range from 0 to 100, with higher values indicating less exposure to chemicals and thus healthier sediments. Values greater than or equal to 93.3 reflect minimum exposure to harmful contaminants.
- Sediments in greater Puget Sound sampled between 1997 and 2022 were in good condition with regard to the measured set of chemicals. SCI measures were above the minimum exposure threshold value.
- Five of six urban bays sampled from 1998 through 2022 also show sediments in good condition or improving. SCI scores in Elliott Bay have improved from baseline sampling in 1998, but still do not reach the threshold level of minimum exposure.
- Sediment contamination typically changes very slowly over time unless contaminant inputs increase. SCI values generally held stable in subsequent rounds of sampling (did not make gains or lose ground relative to the baseline), therefore, progress for this indicator is assessed as No Trend.
- Monitoring Program
Department of Ecology’s Puget Sound Sediment Monitoring Program
- Data Source
Department of Ecology’s Environmental Information Management (EIM) System: Marine Sediments
The Sediment Chemistry Index (SCI) is calculated from measured chemical concentrations in surface sediments as part of the Puget Sound Sediment Monitoring Program. The Department of Ecology's Marine Sediment Monitoring Team (MSMT) samples Puget Sound's marine sediment and organisms living within it once a year, in either April or June, depending on the survey. Fifty sites throughout Puget Sound (see map) are sampled annually to characterize the greater Puget Sound. Sediment chemistry parameters are measured at 10 of the 50 sites each year. A complete set of sediment chemistry data for all 50 Puget Sound sites will be available every five years. In addition, each year the MSMT samples 30 or more sites in one of six urban bays on a rotational basis. Monitoring details are available in the Quality Assurance Monitoring Plan (MSMT, 2023).
The SCI is based on comparisons of measured chemical concentrations to Washington State Sediment Management Standards Sediment Quality Standards (SQS). SQS are sediment chemical concentrations below which adverse biological effects are not expected to occur or above which at least minor adverse impacts on benthic (bottom-dwelling) invertebrates are expected always to occur (Ecology, 2013).
The Index combines data on the concentrations of selected chemicals into an overall index of chemical exposure by calculating the individual ratios of measured contaminant concentrations to their respective SQS and calculating the average, or mean SQS quotient (mSQSq) for a site. The mSQSq is used to calculate the SCI which ranges from 0 to 100, with higher index values indicating less exposure to chemicals and thus healthier sediments (Long et al., 2006; Dutch et al., 2018 Appendix B-1). SCI values above 93.3 reflect minimum exposure levels. This means that most of the samples have no chemicals exceeding their SQS values and the sediment quality is not expected to cause adverse effects on benthic invertebrates.
Sediment Chemistry Index (SCI) categories of exposure to toxicants, based on Mean SQS quotient (mSQSq) critical values.Sediment Chemistry Index (SCI) categories of exposure to toxicants, based on Mean SQS quotient (mSQSq) critical values. SCI Category mSQSm SCI Value Notes Minimum exposure <0.1 >93.3 - 100 Most of these samples have no chemicals exceeding their SQS values. Low exposure 0.1 - <0.3 >80.0 - 93.3 Most of these samples have 1 chemical exceeding its SQS value. Moderate exposure 0.3 - <0.5 >66.6 - 80.0 Most of these samples have 2 or 3 chemicals exceeding their SQS values. Maximum exposure >0.5 0 - 66.6 Most of these samples have ≥3 chemicals exceeding their SQS values. Contaminants measured that contribute to the SCI include metals, polychlorinated biphenyls (PCBs), polynuclear aromatic hydrocarbons (PAHs), and phthalates. Results from other chemicals of concern, such as polybrominated diphenyl ethers (PBDEs), pesticides, dioxins, furans, endocrine-disrupting chemicals, pharmaceuticals, personal care products, and perfluorinated chemicals, for which either no state Sediment Quality Standards have been set or measurements were not taken, are not incorporated into the SCI.
The sediment monitoring statistical sampling design involves unequal sample weighting (MSMT, 2023). That design enables us to estimate spatial extent of conditions for large areas such as bays or the entire Puget Sound region from the conditions at individual sites.
This indicator will be updated every five years for the Sound-wide sampling and every year for the six urban bays rotational sampling.
- Critical Definitions
- SCI scores between 1997 and 2022 for greater Puget Sound met or exceeded the threshold value of 93.3, reflecting minimum exposure to harmful contaminants.
- Elliott Bay sediments remain below the 93.3 threshold value.
- Given that sediment contamination generally changes very slowly, we expect most areas currently meeting the threshold value to continue to do so unless contaminant inputs to the areas increase.
Sediment Quality in Puget Sound story map collection
References cited:
Dutch, M.E., V. Partridge, S. Weakland, D. Burgess, and A. Eagleston. 2018. Quality Assurance Monitoring Plan: The Puget Sound Sediment Monitoring Program. Washington State Department of Ecology. 128 pp. https://fortress.wa.gov/ecy/publications/documents/1803109.pdf
Long, E.R., C.G. Ingersoll, and D.D. MacDonald. 2006. Calculation and uses of mean sediment quality guideline quotients: A critical review. Environmental Science and Technology 40 (6):1726-1736.
Marine Sediment Monitoring Team (MSMT). 2023. Quality Assurance Monitoring Plan: The 2023-2028 Puget Sound Sediment Monitoring Program. Publication 23-03-104. Washington State Department of Ecology, Olympia. https://apps.ecology.wa.gov/publications/SummaryPages/2303104.html
Washington State Department of Ecology. 2013. Sediment Management Standards. Chapter 173-204 WAC. Washington State Department of Ecology, Olympia, WA. Publication No. 13-09-055. https://fortress.wa.gov/ecy/publications/SummaryPages/1309055.html
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No Subcategories for this Puget Sound Indicator.