Study shows simple treatment can protect salmon from toxic urban stormwater runoff

Coho salmon are struggling, but a new report suggests that boosting stormwater treatment could help them in some environments. Photo courtesy USGS.
Coho salmon are struggling, but a new report suggests that boosting stormwater treatment could help them in some environments. Photo courtesy USGS.

Green stormwater infrastructure needed to protect salmon in urban streams

Staff Report

Simple sand and soil filters could prevent much of the pollution from urban runoff that’s killing adult coho salmon in West Coast streams, NOAA researchers found after studying water quality around Puget Sound.

The research traced the link between toxic parking lot runoff and other urban pollution and salmon deaths. More than half the coho salmon returning to urban streams dominated by stormwater runoff die every year before they spawn.

“Untreated urban runoff is very bad for salmon health,” said Julann Spromberg, a research scientist at NOAA Fisheries’ Northwest Fisheries Science Center in Seattle. “Our goal with this research is to find practical and inexpensive ways to improve water quality. The salmon are telling us if they work.”

Coho salmon in California, Oregon and southwestern Washington are listed under the Endangered Species Act and urban pollution may push them closer to extinction. Filtration columns, similar to the rain gardens that are being adopted in urban environments, are part of an emerging green stormwater infrastructure that should be integrated into future development and redevelopment to reverse the trend and help coho recover, the scientists said.

The findings are published in the Journal of Applied Ecology and show that, green stormwater treatment could give wild coho salmon a fighting chance.

“They can’t take the kinds of losses we’ve documented in urban streams,” said Nat Scholz, manager of the Ecotoxicology Program at the NWSFC in Seattle and a coauthor of the study. The scientists tested the effects of pollution by exposing adult coho from a hatchery to different degrees of polluted and clean water, including runoff from a busy urban highway in Seattle. All fish exposed to the highway runoff died within 24 hours.

But after researchers filtered the water through a roughly three-foot-high soil column containing layers of gravel, sand, compost and bark, all the exposed coho survived as well as they did in clean water. Tests showed the filtration columns reduced toxic heavy metals by 58 percent and polyaromatic hydrocarbons, which are byproducts of gasoline combustion, by 94 percent.

“What impressed me most was the effectiveness of the treatment,” said Jen McIntyre, co-author and researcher at the stormwater program at WSU’s Puyallup Research and Extension Center. “It’s remarkable that we could take runoff that killed all of the adult coho in less than 24 hours – sometimes less than four hours – and render it non-toxic, even after putting several storms worth of water through the same soil mixture.”

In an unusual twist, scientists first tried unsuccessfully to create artificial stormwater by mixing up a brew of metals and components of crude oil known from urban runoff. However, the artificial stormwater did not have the fatal effects of the actual highway runoff, with the fish exposed to it surviving as well as they did in clean water.

This suggests that the contents of urban runoff may include as-yet unknown toxins from exhaust, leaking oil and dust from brakes and tires as they wear.

Researchers said it could take years of further testing and analysis to determine precisely what in the runoff is killing the coho. Previous research connected coho mortality rates to the amount of paved surface in a watershed, so the fatal ingredients appear linked to urban runoff and not household or agricultural pollutants such as pharmaceuticals or pesticides.

“The recurring coho spawner deaths have been a high-profile mystery for many years, and we’re now much closer to the cause,” Scholz said. “Although we haven’t identified a smoking gun, our study shows that toxic stormwater is killing coho, and that the problem can be addressed.”

The research was funded by Region 10 of the U.S. Environmental Protection Agency, Washington Sea Grant, NOAA Coastal Storms Program and Puget Sound Regional Stormwater Monitoring Program.

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