Publication Summary

During Wateryear 1991 (October 1990 through September 1991), the Washington State Department of Ecology monitored water quality monthly at 28 stations in Puget Sound, four stations in Grays Harbor, and five stations in Willapa Bay. Of the 28 stations in Puget Sound, 23 sites showed dissolved oxygen concentrations below the water quality standards for marine waters one or more times, and 11 exceeded fecal coliform counts of 14 organisms/100 milliliters (mL) one or more times.

During Wateryear 1991 (October 1990 through September 1991), the Washington State Department of Ecology monitored water quality monthly at 28 stations in Puget Sound, four stations in Grays Harbor, and five stations in Willapa Bay. Of the 28 stations in Puget Sound, 23 sites showed dissolved oxygen concentrations below the water quality standards for marine waters one or more times, and 11 exceeded fecal coliform counts of 14 organisms/100 milliliters (mL) one or more times.

Nutrient depletion was observed at 20 Puget Sound stations. Of the nine coastal stations, none violated dissolved oxygen standards, and four exceeded fecal coliform counts of 14 organisms/100 mL one or more times. Nutrient depletion was only observed at the Willapa Bay stations. Stations that did not experience nutrient depletion as defined by this report, were well mixed and lacked observable ongoing density stratification. At several Puget Sound stations, chlorophyll a concentrations were inversely proportional to nutrient concentrations, with maximum chlorophyll a concentrations and minimum nutrient concentrations observed simultaneously. Chlorophyll a concentrations were highest during the spring and summer months and lowest during late fall and winter months for Puget Sound stations. The coastal stations exhibited two chlorophyll a peaks, one during mid-summer and again in midfall. To assess the quality of the marine water column data, a detailed quality assurance assessment was conducted on the Wateryear 1991 (WY 1991) results. Ninety-four percent of the nitrite results were below detection limits. Discontinuing dissolved nitrite analysis until lower detection limits can be achieved by the laboratory was recommended. The quality assurance assessment also revealed that the fecal coliform bacteria results did not achieve precision objectives in either the field or laboratory replication. Procedures for future collection and analysis of fecal coliform bacteria should be amended to improve the quality of these data. In general, to improve temporal and spatial coverage for shorter term and episodic water quality events not caught by the monthly sampling component of the program, continued monitoring efforts should include a seasonal monitoring component. Sites showing signs of nutrient depletion and/or conditions that promote biological activity (stratification) should be priority candidates for seasonal monitoring.