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

100 samples were compared to the upper prediction limits calculated in the 1997 northern Puget
Sound study (Long et al., 1999a): > 1 1.1 pglg and >37.1 pglg.
Incidence and Severity, Spatial Patterns and Gradients, and Spatial Extent of
Sediment Toxicity
The incidence of toxicity was determined by dividing the numbers of samples identified as either
significantly different from controls (i.e., "significantly toxic") or significantly different from
controls and 4 0% of control response (i.e., "highly toxic") by the total number of samples tested
(i.e., 100). Severity of the responses was determined by examining the range in responses for
each of the tests and identifying those samples with the highest and lowest responses. Spatial
patterns in toxicity were illustrated by plotting the results for each sampling station as symbols or
histograms on base maps of each major region.
Estimates of the spatial extent of toxicity were determined with cumulative distributionfunctions
in which the toxicity results from each station were weighted to the dimensions (km2) of the
sampling stratum in which the samples were collected (Schimmel et al., 1994). The size of each
stratum (km2) was determined by use of an electronic planimeter applied to navigation charts,
upon which the boundaries of each stratum were outlined (Table 1). Stratum sizes were
calculated as the averages of three trial planimeter measurements that were all within 10% of
each other. A critical value of less than 80% of control response was used in the calculations of
the spatial extent of toxicity for all tests except the cytochrome P450 HRGS assay. That is, the
sample-weighted sizes of each stratum in which toxicity test results were less than 80% of
control responses were summed to estimate the spatial extent of toxicity. Additional critical
values described above were applied to the ~ icrotox~~ and cytocl~rome P450 HRGS results.
Concordance Among Toxicity Tests
Non-parametric, Spearman-rank correlations were determined for combinations of toxicity test
results to quantify the degree to which these tests showed correspondence in spatial patterns in
toxicity. None of the data from the four toxicity tests were normally distributed, therefore, non-
parametric tests were used on raw (i.e., nontransformed) data. Both the correlation coefficients
(rho) and the probability (p) values were calculated.
Chemical Analyses
Spatial Patterns and Spatial Extent of Sediment Contamination
Chemical data from the sample analyses were plotted on base maps to identify spatial patterns, if
any, in concentrations. The results were shown with symbols indicative of samples in which
effects-based numerical guideline concentrations were exceeded. The spatial extent of
contamination was determined with cumulative distribution functions in which the sizes of strata
in which samples exceeded effects-based, numerical guidelines were summed.
Three sets of chemical concentrations were used as critical values: the SQS and CSL values
contained in the Washington State Sediment Management Standards (Chapter 173-204 WAC)
and the Effects Range-Median (ERM) values developed by Long et al. (1995) from NOAA's
national sediment data base. Two additional measures of chemical contamination also examined
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