PARENT SESSION
PT9 - Sediments
Tuesday, 19 November 2002
8:00 AM to 6:30 PM
Exhibit Hall

(P676) Sediment Quality Assessment of Three Urban Lakes - Lakes Washington, Sammamish and Union.

Lester, Deborah^*,1, Wilson, Dean¹, ¹ King County Department of Natural Resources, Water and Land Resources Division, Seattle, WA, USA

ABSTRACT- King County recently completed a sediment quality assessment of three urban lakes. Lake Washington (87.6 km2), the largest lake, is located within the greater Seattle Metropolitan area; bordered to the west by the City of Seattle and to the east by a number of smaller cities. Lake Sammamish (19.8 km2), located 15 miles east of Seattle, experiences some of the highest development pressure in the region. Lake Union (2.3 km2), the most heavily urbanized lake, receives runoff from residential, commercial and industrial neighborhoods. Its shores are completely lined by marinas, houseboat moorage, commercial docks and dry-docks and industries. It was believed sediment quality in all three lakes was significantly influenced by a variety of urban contaminants. While a few focused assessments had been completed, a comprehensive sediment quality assessment had not been conducted. As such, the study objectives were (1) conduct a comprehensive baseline sediment quality assessment; (2) evaluate contaminant concentration and distribution; (3) evaluate sediment toxicity; and (4) evaluate benthic community structure. Sediments were analyzed for organic compounds including pesticides and PCBs; metals; tributyltins and conventional parameters. Chemical data were compared to Washington State draft freshwater sediment guidelines and other available guidelines. Three toxicity tests were conducted, Hyalella azteca (survival), Chironomus tentans (growth and survival), and Microtox. Benthic invertebrate samples were collected and organisms identified to species when possible. Some of the highest contaminant levels were found adjacent to stormwater discharges. A number of metals and organic compounds exceeded sediment guidelines; however, toxicity test results did not consistently coincide with these data, suggesting differences in bioavailability. In general, PAHs and metals were the primary contaminants of concern.

Key words: sediment, toxicity, lakes, benthic community