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

samples were collected primarily in Sinclair and Dyes Inlets, inner Elliott Bay, and the
Duwamish.
Relationships between Benthic Infaunal Indices and Sediment
Characteristics, Toxicity, and Chemical Concentrations
The statistical relationships between indices of benthic community structure and selected
sediment characteristics were calculated using Spearman rank correlations. These correlations
were used to determine if any of the measures of benthic community structure co-varied with any
of the sediment characteristics quantified in this study. Measures of naturally occurring sediment
variables such as grain size and total organic carbon (Table 24), toxicity (Table 25), and
concentrations of chemical contaminants (Table 26-32) were included in the correlations with
benthic infauna indices.
Benthic Infauna Indices vs. Grain Size and Total Organic Carbon
Typically, concentrations of trace metals tend to increase with increased percent fines, and high
concentrations of organic compounds are related to higher total organic carbon (TOC)
concentrations. Since higher concentrations of toxic compounds such as trace metals and organic
compounds are generally expected to be related to decreased benthic community abundance and
variability, higher concentrations of fines and organic carbon are also expected to be related to
decreased abundance and diversity. Most of the indices of benthic infauna abundance and
diversity followed the expected pattern, with statistically significant decreases correlated with
increasing percent fine-grained particles and TOC content (Table 24). Taxa richness, Swartz's
Dominance Index, mollusc abundance, and miscellaneous taxa abundance displayed the highest
significant negative correlations with both percent fines and TOC (rho=-0.358 to -0.374, pO.001
and rho=-0.4 1 to -0.66, pg.000 1 ). Inverse correlations were also apparent between total
abundance vs. percent fines, evenness vs. TOC, and arthropod abundance vs. both percent fines
and TOC, but at a lower level of significance (rho=-0.219, p0.05 and -0.26 to -0.3 16, pO.01).
Relationships between total abundance vs. TOC, Pielou's evenness vs. percent fines, and annelid
and echinoderm abundance vs. both percent fines and TOC were not significant.
Benthic Infauna Indices vs. Toxicity
Examination of Table 25 indicated the following relationships between benthic infauna indices
and toxicity. None of the indices of benthic structure were significantly correlated with percent
amphipod survival. Percent urchin fertilization showed a highly significant negative correlation
with annelid abundance (rho=-0.39 1, pO.000 1) and to a lesser extent with total abundance
(rho=-0.29, ~9.01). That is, as percent fertilization decreased in laboratory tests (i.e., increasing
toxicity), the abundance of annelids and all organisms in the benthic samples increased. These
negative correlations were counter to what would be expected, and may be related to very high
numbers of toxicant-tolerant species of annelids, such as Aphelochaeta, in some of the samples.
Results of the microbial bioluminescence tests were positively correlated with taxa richness
(rho=0.306, pg.Ol), Swartz's Dominance Index (rho=0.257, pO.Ol), and the abundance of
molluscs (rho=0.286, pg.Ol), but negatively correlated with the abundance of echinoderms
(rho=-0.285, pO.01). These correlations indicated that as MicrotoxTM EC50 values decreased
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