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Preserving Eelgrass While Remediating Legacy Contamination

Eelgrass

What do you do when the State requires you to take action, yet prohibits that action? It’s a conundrum that takes imagination and determination.

The Setup

For over 100 years, several companies used the nearshore at the former Custom Plywood site for processing and manufacturing wood-related materials that would be used nationwide. They filled the tideland with wood, ash, bricks, metal, and sediment. They left a tug, boiler ash, scrap metal, barrels and drums, aluminum cans, scrap wood, paper, sawdust and creosote-treated pilings. As if that wasn’t enough, in 1992 a fire destroyed the mill, adding dioxin (a carcinogen) to the sediment.

The Conundrum

The Washington State Department of Ecology and Hart Crowser removed most of the contamination from the property and tidelands. Despite this, there are many acres of tidelands that are still peripherally contaminated with dioxins, much of which contains healthy eelgrass habitat. The eelgrass is not affected by the dioxin contamination; the problem is that it serves as a potential pathway for human exposure (i.e., shellfish consumption). By State mandate eelgrass must be protected. (See our earlier post about the importance of eelgrass). This means that the State requires that something be done about the contamination but not at the expense of the valuable eelgrass habitat. Our current options for dealing with dioxin contamination are to either dig up the contaminated material, or immobilize/cover it to prevent the exposure to the benthic community. Either action would potentially destroy the eelgrass. What to do?

The New Approach

The solution? Remediate the sediment in place by covering the eelgrass habitat, but not burying it. Eelgrass, unlike other species of seagrass, can only tolerate a very small level of burial. We needed to determine if the eelgrass at the former Custom Plywood site could withstand deposition of very fine layers of sand that would act as a barrier (cap) to the contamination in order to protect the benthic community and the habitat overall. Our team conducted a two-year pilot study to see whether the eelgrass could tolerate a four- or eight-inch layer of sand (applied two inches at a time), rather than a single layer application that would ordinarily be used for remediation. As part of this study, our team also investigated if adding a layer of carbon could increase the cap performance so that the cap could be as thin as possible.

Diver

Diver with eelgrass/sediment sample. Photo courtesy of Research Support Services.

The Result

The data clearly showed that eelgrass at the former Custom Plywood site can survive a four-inch cap if implemented in multiple thin layers. This means that the preferred alternative for cleaning up the residual contamination is potentially feasible. The next step is to design a large scale application using the information and data gathered from the pilot study. Eventually we hope to finally cleanup the former Custom Plywood site while leaving the existing eelgrass habitat in place and functioning.

 

Three Reasons Eelgrass is Declining—What’s Being Done?

Dredging

In an earlier post we showed how important eelgrass is to fish, and noted that eelgrass is declining worldwide. West coast eelgrass is affected by a combination of coastal development and nutrient pollution, direct displacement (such as dredging activities), and climate change.

Here’s why:

Eelgrass needs light. Urbanization and construction activities in coastal areas remove vegetated buffers, allowing more runoff into the water. Runoff carries sediment, which reduces water clarity. Also, nutrients from wastewater, stormwater, and other human activities can promote algae blooms, which also block light.

Dredging uproots eelgrass; filling buries it. These activities can completely decimate an eelgrass meadow even beyond the footprint of direct impact. It can take ten years or more for eelgrass to recover, if at all.

Climate change: as ocean temperatures rise, native plants feel the heat. Evidence shows that northern eelgrass populations will not adapt to warmer waters as easily as southern eelgrass populations might. Their photosynthetic engines just can’t keep cool enough. Also, as a consequence of climate change, sea level is rising, meaning eelgrass will have to move to keep the same relative depth. It can’t move far before a hardened structure such as bluff or even a seawall stops it.

The State of Washington is acting to restore eelgrass across Puget Sound. The Puget Sound Leadership Council established a target of expanding the total area of eelgrass beds by 20 percent by 2020. Major restoration efforts have already been undertaken, and more are underway. New plantings are proposed for the Nisqually, Skokomish and Elwha river deltas. In these places, restoration may have a better chance to succeed because of improved sandy substrate and restored water quality.

Section3B_Marine-Nearshore_AcresEelgrass

Acres of Eelgrass in Puget Sound

More information: shedding new light on eelgrass recovery and threats and human impacts on eelgrass.

Eelgrass—Nowhere to Hide

Bay Pipefish in Eelgrass

Bay Pipefish (Syngnathus leptorhynchus)–one of many species that depend on eelgrass habitat for survival.

A marine ecologist in Hart Crowser’s Anchorage, Alaska office, overheard a recent complaint, “When I go fishing I can’t stand all this ‘eelweed’ getting in my prop and fouling my lines.”

“Then why do you fish where there is eelgrass?” asked the marine ecologist.

“Because that is where fishing is best.”

That was the crucial connection. Eelgrass is essential fish habitat. Without it, even migratory fish (including our beloved salmon), don’t have a place to call home.

Eelgrass (Zostera marina) is native to shallow waters of most temperate oceans and seas, including Puget Sound, Oregon, northern California, British Columbia, and Alaska. It is not a seaweed like kelp, but a flowering plant that evolved from terrestrial flora (similar to what you might find in your front yard).

Eelgrass is important to many fish and invertebrates. Juvenile salmon, rockfish, and Dungeness crab find shelter in eelgrass meadows in early life. Herring, in particular, spawn on eelgrass, making it crucial to its survival. Many species (including commercially important ones) use it to live, eat, spawn, and hide from predators.

Eelgrass is also very good at converting carbon dioxide into tissue that may get buried, taking it out of the system (blue carbon). An acre of eelgrass can remove nearly 150 kg of carbon from the atmosphere every year, making it important to the issues of ocean acidification and global climate change.

Eelgrass is pretty hearty, dealing with coastal storms, being exposed at low tide, and spending part of each year under sea ice (in northern areas). Yet, as hearty and important as eelgrass is, it is on the decline, leaving fish and invertebrates that depend on it with nowhere to hide. Stay tuned for the reasons why, and what’s being done about it.