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Before the arrival of Europeans to their Nation, the Tsleil-Waututh, “People of the Inlet,” gathered over 90 percent of their food from the marine environment of Burrard Inlet, British Columbia. Staples included salmon, herring and shellfish such as clams. Throughout the inlet, there are numerous sites of former camps and settlements, many evidenced by shell middens—collections of discarded remnants of clams, oysters, mollusks and other refuse built up over hundreds, even thousands, of years.

The alkaline properties of shell middens reduce the acidity of their environments and not only preserve the archeological evidence in their midst, they may also provide a key to helping reduce the acidity of surrounding ocean sediment and restoring former areas of bivalve habitat.

Simon Fraser University (SFU) Marine Ecology and Ecotoxicology Professor Leah Bendell investigates the effects of stressors on the natural environment. For over 30 years, she has studied how anthropogenic impacts alter ecosystem structure and function and the consequences of such impacts on ecosystem and human health. She has also collaborated with numerous conservation groups and stakeholders from around the Salish Sea to gather evidence and advocate for better care of local waters.

Bendell and graduate student Bridget Doyle recently partnered with the Tsleil-Waututh Nation to study whether the addition of shell hash would restore or sustain traditional food sources in Burrard Inlet. The investigation was informed by elements of Indigenous knowledge and traditional management techniques and conducted on two sites—Maplewood Mudflats and Whey-ah-Wichen/Cates Park. Both of these are within ancestral Tsleil-Waututh territories.

The study, An evaluation of the efficacy of shell hash for the mitigation of intertidal sediment acidification, co-authored with Doyle, found that the addition of shell hash helped regulate the variation in sediment pH, an important finding in the understanding of bivalve habitat.

We met with Professor Bendell to discuss her research.

Can you describe what effect the addition of shell hash had on these two sites?

It was dependent on the type of sediment; sediment high in organic matter—like that of Maplewood Mudflats—did not respond as well as sediments that were more cobble-like, as they were at Whey-ah-Wichen/Cates Park. For the cobble sediment, the shell hash was able to reduce the variability in pH that occurs throughout the low and high tidal cycles. From here, we were able to determine that the degree of success will be dependent on the site and the existing habitat.

Your paper mentions that eutrophication, the death of animal life from lack of oxygen, is occurring at the study sites and around the inlet. Why this is happening?

Those areas of the intertidal that receive excess nutrients for example through sewage discharge, will be subject to excess seaweed growth as a result of the seaweed taking advantage of the extra nutrients available to them. When the seaweed is exposed on the intertidal for long periods of time—such as low tides—it will die and decompose, using up oxygen at the sediment/water interface. When that happens, animals that live in the sediment/water interface that need that oxygen will also die.

Is it possible to restore healthier bivalve growing conditions to Burrard Inlet, and what would we need to do?

Absolutely, and the Tsleil-Waututh Nation are way ahead on this. First and foremost is to restore as much of the intertidal and estuarine habitat of the inlet as possible. That would include removing structures such as cement walls and wharves. Once access to the intertidal can be reestablished, planting of eelgrass, and sedges and allowing for natural sedimentation processes to occur will start the restoration process. Nature can heal. It just needs time.

Will you continue this line of investigation into the use of shell hash? What other research projects are you working on?  

Likely not shell hash as Doyle’s study was able to demonstrate how this approach can or cannot be used effectively to help ameliorate sediment acidification. My current projects are looking at the movement of microplastics through intertidal food webs and the risks that these unique pollutants present to our marine ecosystems. We are in our infancy in the understanding of these complex contaminants and much work is needed to determine the risks they present and how we can mitigate those risks.

For more: Learn about the Tsleil-Waututh Nation and read Bendell’s article in the Conversation Canada.

This study was conducted within the shared ancestral and unceded territories of the səl̓ilwətaɁɬ (Tsleil-Waututh; TWN), xʷməθkʷəy̓əm (Musqueam), and Sḵwx̱wú7mesh (Squamish) Coast Salish Nations. The investigation was informed by elements of Indigenous knowledge and traditional management techniques with the intent of restoring or sustaining traditional food sources and ecosystem services under changing coastal conditions in a culturally appropriate way.

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