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

Spatial Extent of Toxicity
Discussion
The survey of sediment toxicity in central Puget Sound was similar in intent and design to those
performed elsewhere by NOAA in many different bays and estuaries in the U. S. using
comparable methods and to the survey conducted in northern Puget Sound (Long et al., 1999a).
Data have been generated for areas along the Atlantic, Gulf of Mexico, and Pacific coasts to
determine the presence, severity, regional patterns and spatial scales of toxicity (Long et al.,
1996). Spatial extent of toxicity in other regions ranged from 0.0% of the area to 100% of the
area, depending upon the toxicity test.
The intent of this survey of central Puget Sound was to provide information on toxicity
throughout all regions of the study area, including a number of urbanized/industrialized areas.
The survey area, therefore, was very large and complex. This survey was not intended to focus
upon any potential discharger or other source of toxicants. The data from the laboratory bioassays
were intended to represent the toxicological condition of the survey area, using a battery of
complimentary tests. The primary objectives were to estimate the severity, spatial patterns, and
spatial extent of toxicity, chemical contamination, and to characterize the benthic community
structure. A stratified-random design was followed to ensure that unbiased sampling was
conducted and, therefore, the data could be attributed to the strata within which samples were
collected.
Four different toxicity tests were performed on all the sediment samples. All tests showed some
degree of differences in results among the test samples and negative controls. All showed spatial
patterns in toxicity that were unique to each test, but also overlapped to varying degrees with
results of other tests. There were no two tests that showed redundant results.
Amphipod Survival - Solid Phase
These tests of relatively unaltered, bulk sediments were performed with juvenile crustaceans
exposed to the sediments for 10 days. The endpoint was survival. Data from several field
surveys conducted along portions of the Pacific, Atlantic, and Gulf of Mexico coasts have shown
that significantly diminished survival of these animals often is coincident with decreases in total
abundance of benthos, abundance of crustaceans including amphipods, total species richness, and
other metrics of benthic community structure (Long et al., 1996). Therefore, this test often is
viewed as having relatively high ecological relevance. In addition, it is the most frequently used
test nationwide in assessments of dredging material and hazardous waste sites.
The amphipod tests proved to be the least sensitive of the tests performed in central Puget Sound.
Of the 100 samples tested, survival was significantly different from controls in 7 samples.
Samples in which test results were significant were collected at stations widely scattered
throughout the study area. The data showed no consistent spatial pattern or gradient in response
among contiguous stations or strata. There was one sample in which survival was statistically
significant and mean survival was less than 80% of controls; the response level was determined
empirically to be highly significant (Thursby et al., 1997).
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