Dumas Bay: Stinky and stymied

For more than a year, Federal Way has pushed to obtain funding to rid Dumas Bay and its beach of noxious seaweed.

An agreement with the state’s Department of Ecology to fund the removal was approved by the city council Aug. 5. But the city is unsure if the removal will take place, and also unsure how one of the sources causing the seaweed mass is entering the bay.

If the smell caused by the decomposing algae becomes too overwhelming, a Department of Ecology contractor will remove the growth. The project will cost Federal Way up to $50,000, from the City Manager Contingency Fund, and will cost the Department of Ecology the same. The removal could occur anytime between now and Oct. 31, said Ken Miller, Federal Way public works deputy director said.

Mischievous outburst

The seaweed explosion occurs when an increase in light and nutrients, such as nitrogen, are introduced to the water. The combination causes the plant to grow in layers. Those that do not receive adequate oxygen begin decomposing and when torn apart by waves, animals or humans, they release hydrogen sulfide. The gas produces a stench similar to rotting eggs or sewage.

Typically, the seaweed in Dumas Bay stretches along the shore for more than half a mile and into the water for an unknown length, said Dan Smith, Federal Way Surface Water Quality Program Coordinator. The plant is producing at a rate of several tons per day, according to the interlocal agreement.

In the summer months, natural nitrogen levels in the bay usually decrease, said Ron Thom, staff scientist with Marine Sciences Laboratory of Pacific Northwest National Laboratory. When nitrogen from outside sources is introduced, the seaweed growth is propelled, he said.

“If you get some nitrogen addition in these areas that are limited, you tend to increase the growth rate of these plants,” Thom said.

This will be the first time removal of the seaweed will occur in Dumas Bay.

“It’s somewhat of a pilot project,” Miller said. “We are hoping to be able to do it to see how it works and if it works.”

Disposal efforts

A similar project may soon occur in Seattle’s Fauntleroy Cove.

In the past at this location, a contractor has collected the overgrowth and transported it to deeper waters, where the load was dumped with the anticipation that it would sink to the bottom of the cove and remain undisturbed.

This time around, the Department of Ecology decided to dispose of the seaweed on land. At Dumas Bay and Fauntleroy Cove, the contractor, Blue Marble, will use a pump and net to suction the surface seaweed and load it onto watercraft. From there it will be transported to a land destination for final disposal. The cost to dump the seaweed on land would be approximately $40 per ton, said former Federal Way surface water manager Paul Bucich in May 2007, when the city first began pursuing the project.

Hauling the seaweed out of the water will provide a temporary solution. Though it is known what causes the seaweed to smell, studies have not been completed at Dumas Bay to determine the source of the nutrients feeding the growth.

“Where do the nutrients come from? Is it a natural thing or man introduced? We don’t know,” Miller said.

For approximately $50,000, scientists can conclude the chemical signature of the seaweed overgrowth, Thom said. A circulation study to measure the concentration of nitrogen would be needed, he said.

The study would determine if breaking apart the seaweed is reintroducing the nutrients into the water and making more seaweed grow, or if the nutrients are inorganic.

Inorganic nutrients could come from fertilizers or treated wastewater, for example. Wastewater treatment plants, no matter how careful they are, add some degree of nutrients to water bodies they discharge into, said Dave McBride, Washington State Department of Health toxicologist. But the reason why there is more growth in Dumas Bay is probably due to fertilizer run-off, McBride speculated.

Reoccurring predicament

Seaweed overgrowth is a common problem worldwide, but testing to determine its source has not taken place at Dumas Bay or Fauntleroy Cove.

“Nobody’s willing to pay for the research,” Thom said.

Miller said he was not aware that this testing was available. He planned to inquire about it with the Department of Ecology, but said the contract to remove the seaweed belongs to the department, not the city.

Until the source feeding the seaweed barrage is pinpointed, it will likely pop up annually when the days become longer.

“It’s like pulling weeds out,” Smith said. “It looks good for a while, but they come back.”

Contact Jacinda Howard: or (253) 925-5565.

Disposal of seaweed costs the same as a test to determine its cause, scientist says

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