Sediment Quality in Puget Sound Year 2 - Center for Coastal ...

Triad Synthesis: A Comparison of Chemistry, Toxicity, and Infaunal
Parameters
To generate a more comprehensive picture of the quality of the sediments throughout the study
area, a weight-of-evidence approach was used to simultaneously examine all three sediment
"triad" parameters measured. Data from the toxicity testing, chemical analyses, and benthic
community analyses from all stations were combined into one table (Appendix H) for review.
From this data compilation, thirty-six stations were identified in which at least one chemical
concentration exceeded an ERM, SQS, or CSL value and at least one of the toxicity tests
indicated statistically significant results relative to controls (Table 33). These stations were
located in Port Townsend (I), the central basin (3), the Bainbridge Basin (2), Dyes Inlet (2),
Sinclair Inlet (6), and Elliott Bay and the Duwamish River (22). Together, these stations
represented an area of 99.73 km2 or about 14% of the total survey area.
Twenty-five stations showed no indications of significant sediment toxicity or chemical
contamination (Table 34). These stations were located in Port Townsend (1 ), Admiralty Inlet (3),
Possession Sound (2), the central basin (3), Port Madison (3), Liberty Bay (3), the Bainbridge
Basin (4), Rich Passage (3), Dyes Inlet (I), and outer Elliott Bay (2). These 25 stations
represented an area of 359.3 1 km" equivalent to 49% of the total survey area. Both sets of
stations are highlighted in Figures 38-42.
The remaining thirty-nine stations displayed either signs of significant chemical contamination
but no toxicity, or significant toxicity, but no chemical contamination. These stations were
located in Port Townsend (4), Possession Sound (I), the central basin (lo), Eagle Harbor (3),
Liberty Bay (3), the Bainbridge Basin (6), and Elliott Bay and the Duwamish River (12).
Together, these stations represented an area of 272.62 km2, equivalent to 37% of the total central
Puget Sound study area.
The complete suite of triad parameters for all stations was examined to determine whether the
infaunal assemblages, as characterized by benthic indices, appeared to be impacted by the
presence or absence of toxic compounds. Details regarding the "triad" relationship for all 100
stations are summarized below.
Examination of the six stations from the two strata in Port Townsend indicated that one station,
106, had both significant toxicity results and elevated chemical contamination, and one station,
1 10, had no significant results. Sediments from stations 106- 108 (stratum 1 ) and stations 109-
11 1 (stratum 2), situated in southern and northern Port Townsend respectively (Figure 38), were
collected from depths ranging from 13-34m, with sediment types ranging from primarily sand to
primarily silt-clay particles. All (with the exception of station 1 10) had levels of 4-methylphenol
above state SQS and CSL criteria. No toxicity was displayed at these stations, with the exception
of significantly reduced amphipod survival at station 106. Measures of infaunal diversity at these
6 stations were, in most cases, high and similar between stations, with little similarity in the
dominant species list from station to station. Station 106, which displayed both impacted
toxicity and chemical measures, also displayed the lowest total abundance (302 individuals), but
exhibited a relatively high SDI (20). Several of the 10 numerically dominant species were those
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