Puget Sound’s growing nutrient problem

An algae bloom covers a huge section of Lake Erie. Photo courtesy of NASA.

An algae bloom covers a huge section of Lake Erie. Photo courtesy of NASA.

First there was “The Blob” that fed last year’s massive algae bloom in the Pacific Ocean. Now there is another monster getting our attention. You might call it “The slime that ate Lake Erie.”

The incredible images of Lake Erie’s expanding blanket of green show the familiar effect of nutrient pollution. Nutrients such as phosphorous and nitrogen have been flowing into the giant lake primarily from sources like agricultural fertilizer and wastewater. This has led to a 700-square-mile algae slick, alarming officials worried about potential buildups of dangerous algal toxins or areas of low oxygen known as “dead zones.”

This sort of thing is well-known in the Pacific Northwest. Decades ago, Lake Washington faced a similar problem due to unchecked dumping of human waste that made the lake un-swimmable and prone to green slime and bacteria. At one point, an estimated 20 million gallons of sewage per day flowed directly into Lake Washington. Then, in the 1960s the city of Seattle initiated tighter pollution controls that diverted sewage to treatment plants, cutting the amount of raw sewage entering the lake to virtually zero.

Lake Washington is often touted as a pollution control success story, and other water bodies like Puget Sound have followed suit. Despite occasional high profile overflows like last year’s massive sewage spill at the West Point Treatment Plant, most of the wastewater that flows into Puget Sound is now treated in some way. (The state is also taking comments on a rule that would make it illegal for boats to discharge treated or untreated waste into Puget Sound.) Parts of Canada still release raw sewage into our shared waters to the north, although Victoria, B.C. finally approved development of a tertiary sewage treatment plant last year.

Scientists will be quick to tell you that, at the very least, some sewage treatment is better than no treatment. It filters many of the potential pathogens that can come with raw sewage, and a whole lot more. But what about those nutrients?

What most of Puget Sound’s sewage treatment plants don’t remove — at least to a significant degree — are nutrients. At most normal levels, these nutrients are natural and essential for the health of the ecosystem. However, when there are too many of them, problems can occur not unlike the situation in Lake Erie.

Image from the Salish Sea Model. Courtesy of the Pacific Northwest National Lab, the Washington State Department of Ecology and U.S. Environmental Protection Agency.

Image from the Salish Sea Model. Courtesy of the Pacific Northwest National Lab, the Washington State Department of Ecology and U.S. Environmental Protection Agency.

For a long time, Puget Sound was thought to be big enough to handle the nutrient load from its wastewater treatment plants and other sources. Now, a new mathematical model shows that we are coming up against the limits of the system. The region is expected to grow by more than 1.5 million residents within the next two decades, putting huge strains on wastewater infrastructure. Add to that climate change that may lower stream flows that normally help to circulate and mix the water in Puget Sound. The model says these two factors will contribute to nutrient build-up and will likely mean increasing problems with water clarity and dissolved oxygen throughout the Sound.

The region is once again at a turning point. Officials say current levels of sewage treatment are not enough.

“Puget Sound’s health is degrading due to increasing levels of nutrients that are adversely affecting water quality,” reports the Washington Department of Ecology on its website. “We are finding that nutrients in Puget Sound are out of balance altering some of its fundamental physical, chemical, and biological functions.” The imbalance could affect sensitive plants like eelgrass as well as salmon and forage fish sensitive to low oxygen, Ecology says.

Ecology is now working on a nutrient source reduction project, and in 2018 is expected to use that research to help guide a collaborative “implementation strategy” related to the state’s Marine Water Quality “Vital Sign”. Watch for more coverage of nutrients here and in our online Encyclopedia of Puget Sound as the story develops.

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