Northwest Fisheries Science Center

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Document Type: Report
Center: NWFSC
Document ID: 9245
Title: Effect of Lake Washington sediment from the Sand Point dredging site on coho salmon (Oncorhynchus kisutch) fingerlings
Author/Editor: Donovan R. Craddock, Joanne G. Parker, Clifford A. Spjut, George F. Slusser
Year: 1978
Institution: Northwest and Alaska Fisheries Center Processed Report

A study was made of the effect of different concentrations of sediment from the NOAA Sand Point dredge site on the survival of coho salmon (Oncorhynchus kisutch) fingerlings and on water quality.  Sediment from the dredging site was mixed in concentrations from 1-60 g/L and from 70-110 g/L for bioassays in lake and dechlorinated city water.  Aerated and circulated bioassays and static bioassays were conducted.  No mortalities occurred in circulated concentrations up to 60 g/L over an exposure period of 192 h.  Increasing the concentrations to 110 g/L still did not obtain an LC50 after 192 h, but some mortalities did occur.  Only one mortality occurred in the static bioassays at concentrations up to 60 g/L and an exposure of 96 h.  Oxygen and pH levels fell sharply in this test, but did not result in mortalities.

The water quality study revealed that the high concentrations of sediment did not deplete the oxygen nor alter the pH appreciably over a 96-h period.  The settleable material dropped out rapidly whereas the total non­filterable residue remained high for 48 h and the turbidity was still high at the end of 96 h.

High concentrations of Lake Washington sediment did not cause mortalities of coho salmon fingerlings approaching LC50 even after 192 h exposure.