Eelgrass at BI Superfund site: to restore or not restore?

Eelgrass, a humble aquatic flowering plant that recently made headlines for its newfound ability to cut down dangerous pathogens in seafood, is a slippery superstar of Puget Sound.

Beds of the seagrass provide food, shelter, resilience and filtration to the intertidal zone, which is why an EPA toxic waste cleanup crew on Bainbridge Island is taking its survival seriously.

The Environmental Protection Agency is charged with de-funkifying the Eagle Harbor Superfund Site, an area just south of the ferry terminal that was once home to the Wyckoff creosote plant. EPA has a decades-long, multi-pronged approach that involves significant human intervention measures, but experts determined that some of the recovery process is best left up to nature, said Bernadette Wright, the project manager.

“This whole area of the site was selected for this kind of remediation that we call ‘monitored natural recovery,’ which is basically saying, ‘We think that this portion of the site will clean itself up through natural processes, but we’re going to continue to look at it periodically to make sure that that’s happening,” Wright said. “And — spoiler alert — it’s not happening in the timeframe that we expected…, so now we are doing some active remediation in that area. That’s where the eelgrass comes in.”

Underwater meadows of eelgrass harbor and feed almost 400 species, including juvenile and spawning fish, invertebrates like crabs and mussels, birds and more. Their roots stabilize the sandy shallows and reduce wave action on shores, which protect the coastline. And they can absorb and filter polluted runoff—creating clear, clean water— and sink 18% of the carbon absorbed globally by the ocean, despite covering only about 1% of the sea floor.

The plant’s value can’t be overstated, said Dianne Sanford, eelgrass researcher with SeaChange Marine Conservation Society in British Columbia. “Seagrass ecosystems are among the most diverse and productive ecosystems in the world. In ecological and economic value, they rival tropical rainforests and the world’s richest farmlands,” she said.

That’s why the EPA is taking steps to ensure that the eelgrass at the Wyckoff site is able to thrive during its remediation efforts. In order to treat certain areas of the site, the EPA must temporarily replace a cofferdam, a watertight enclosure that is pumped dry to permit construction below the waterline. But building a cofferdam on a healthy eelgrass bed would be like clearcutting a patch of old-growth forest, so the agency is looking at transplanting.

EPA scientists did a baseline survey at Wyckoff in 2023 that found about 22 acres of eelgrass, the majority of which is the Washington native species Zostera marina. Small patches of a non-native eelgrass, Zostera japonica, grow close to the shoreline, but the two don’t usually compete; marina prefers deeper water.

“We were very worried that we were basically going to have a wall of eelgrass inside our cofferdam, but what we found is, it’s actually not very much of that native eelgrass inside the footprint,” Wright said. “One of our questions was, ‘Should we be thinking about replanting eelgrass after we remediate?’ And basically what the survey has told us is, we wouldn’t expect the marina to grow in those upper tidal areas anyway, and the japonica will repopulate itself.”

In March, the EPA began its pilot eelgrass transplant study, in which scientists will test the two different transplanting methods and follow up at three-month-, one- and two-year intervals. Eelgrass restoration projects are a longtime conservation goal of the state and environmental groups, but they can be hit or miss. The plants are sensitive, and disturbance from development or heavy pollution can destroy them. Sanford has dedicated over 20 years to learning about transplanting eelgrass, and she is still learning, she said.

“The science of mitigation and restoration of habitats is in its infancy. It is very difficult to re-create a complex habitat type that has its own unique blend of chemical, physical and biological attributes. The successful creation and/or restoration of eelgrass beds has a great deal of uncertainty associated with it,” she said. “However, in some areas, these efforts have been fruitful. Having access to historical information about where eelgrass beds have grown in the past is a helpful tool in guiding where to pursue restoration efforts.”

Fortunately, the thick mat of eelgrass around the Wyckoff site seems to be an indication of good habitat, Wright said. Eelgrass doesn’t take up inorganic chemicals, which means that despite its location, the contaminated waste doesn’t affect it. “The fact that there is such a lovely bed of eelgrass that surrounds the site is really a testament to the geomorphology and the water quality of the site itself,” she said.