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TP9 Urban Watershed Assessment - A Pacific Northwest (USA) Example
() Sediment Quality Triad (SQT) Analysis of Three Urban Western Washington Lakes.
Moshenberg, K1, Brett, M1, Lester, D2, Wilson, D2, 1 Civil & Environmental Engineering, Seattle, WA, 981952 King County Department of Natural Resources and Parks, Seattle, WA, 98104
ABSTRACT- The Sediment Quality Triad (SQT) approach to sediment quality evaluation was used to characterize and assess the extent of altered benthic invertebrate assemblages, sediment contamination and toxicity in Lakes Sammamish, Washington, and Union near Seattle, Washington. Synoptic sediment samples (n=63) from 58 stations were collected in 1999-2001, analyzed for chemical contaminants, and used to conduct 10-day acute sediment bioassay tests on Hyalella azteca mortality and Chironomus tentans growth and mortality. The benthic community composition in these samples was also determined. These lakes lie along an urban gradient with Lake Union being the most impacted and Lake Sammamish the least impacted. Results of principal component analysis (PCA) demonstrated good correlations at many of the sites between SQT components, particularly between the PAHs and C. tentans growth. Stations were determined to be impacted after comparison to controls and a reference envelope developed from non-impacted sites within the study area. Significant toxicity for at least one of the three endpoints occurred at 18 of the stations. Toxicity frequently corresponded to elevated contaminant concentrations when compared to Floating Percentile Sediment Quality Values (FPSQVs) or threshold and probable effects levels (TEL/PEL). In particular, toxicity was associated with elevated concentrations of a subset of contaminants, especially PAHs, Zn, Cu, and TBT. Spatially, the stations exhibiting toxicity were frequently located in close proximity to combined sewer outfalls or decommissioned industrial sites which previously released contaminants. Sediment from these Seattle area lakes exhibited relatively low toxicity when compared to the toxicity results from other lakes (e.g., Lakes Champlain, Ontario, and Roosevelt).
Key words: benthos, Sediment Quality Triad, sediment toxicity, urban lakes
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