Watershed shows decrease in pollutants

April 9, 2013

By Peter Clark

Local protection of natural streams appears to be lessening the presence of pollutants in the regional Cedar-Sammamish watershed.

A new cooperative study, released by the state departments of Agriculture and Ecology, has found that pesticides and insecticides have decreased in the watershed in the past 10 years, thus allowing a healthier environment for salmon in the region.

The Surface Water Monitoring Program for Pesticides in Salmon-Bearing Streams study, released at the end of February, was the third triennial report that began by surveying the five affected watersheds in 2003. Looking into watersheds all over the state, the study team wanted to monitor three different types of rural areas and two urban ones, including the runoff from the Cedar-Sammamish watershed that flows into Thornton Creek.

The creek is 18 miles of urban creeks and tributaries from Southeast Shoreline through northeast Seattle to Lake Washington.

“It would be impossible to monitor every water site,” said Debby Sargeant, project lead on the study. “Thornton Creek represents the typical profile you would find in King County.”

She said the 10 years of data on the site allowed the Department of Ecology to spot the positive trends in decreasing pollutants.

“Significant decreasing trends in pesticide concentrations were seen at Thornton Creek,” the report said, listing the specifics chemicals diazinon, diuron, mecoprop and triclopyr.

The data signifies a boon to the salmon and other marine animals that live in the watershed. The study explored the concentrations in pesticides that can occur in the winter and early spring. Through the spring, rainwater and thaws in the mountains wash pesticides and insecticides away.

Of local concern is the summer salmon habitat in Thornton Creek, requiring suitable water temperature and lack of pesticides.

“All of the observed pesticide trends for Thornton Creek were for decreasing concentrations over time,” said the report. It marked a 36 percent drop per year in insecticides and at an average 12 percent drop per year in herbicides.

In 2004, the EPA began phasing out usage of the insecticide diazinon, which Sargeant credited for the decrease in its presence in the watershed. As for the herbicide fall off, however, she was less sure.

“I just don’t know,” she said while laughing and speculating a bit on the reasoning. “King County has a number of programs for integrated controls, so maybe the public is a factor.”

Though the report highlighted beneficial news for the area, it still left room to show concern regarding aspects of the study.

“None of the project area sites consistently met standards for water temperature,” it read, citing the decrease in oxygen and high temperatures as worrisome to habitat.

The agriculture department will add five increasing pesticides to its list of concern, expanding their testing to ensure healthy habitats of the watersheds.


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