Oil Spill response Techniques for BC Coastal Wetlands

Oil Spill response Techniques for BC Coastal Wetlands

The risk of accidental oil spills in British Columbia coastal waters will increase in the future as a result of (a) proposed oil exports from British Columbia, (b) increased marine shipping and large vessel traffic and (c) proposed offshore oil exploration and production. Coastal and estuarine wetlands are special features that are particularly sensitive to oil spill impact and cleanup. These features are relatively uncommon on the coast, comprising less than 10% of the total coastline length, are known to retain significant amounts of oil when inundated by a spill, are difficult to cleanup and are important wildlife habitat.

The BC ShoreZone system maps the occurrence and linear extent of coastal wetlands but does not generally subcategorize or classify wetland types or document aerial extent of the wetlands. The classification system of MacKenzie and Moran (2004) identifies typical vegetation assemblages (site associations) of BC wetlands but has not been used as a mapping framework. Actually there is no uniform mapping and classification system that has been applied to BC coastal wetlands and most remain unclassified.

No specific studies of oil spill effects or impacts on BC wetland species assemblages were found. Much of the research of effects of wetland oil spill and cleanup techniques has been done in Spartina-dominated areas. Spartina has very different morphology and characteristics than any native Pacific Northwest wetland vegetation, making it difficult to extrapolate those studies to BC situations. Studies of BC examples of wetlands oil spill and clean up effects are recommended, to evaluate the response of local species to these disturbances. The results of those studies could potentially be extrapolated to other areas in southeast Alaska or northern Washington where similar wetland species assemblages occur.

For the purposes of spill response planning, three broad categories of BC coastal wetlands were identified based on general characteristics: (a) riverine, spatially complex wetlands (e.g., Fraser River Delta, Cowichan River delta) where estuarine wetlands have developed complex patterns in the meandering channels of the deltas, (b) alluvial delta wetlands, where fringing wetlands occur along the upper intertidal area of the numerous alluvial fans on the otherwise steep coastline (e.g., west coast Vancouver Island, and Haida Gwaii) and (c) marine lagoon/tidal flat wetlands that are typically associated with spit and lagoon complexes. These general wetlands types provide a useful framework for generic spill response planning.

In terms of spill countermeasure planning, general guidelines typically recognize the uniqueness of each wetland setting and that wetlands are very sensitive to cleanup operations (Hoff 1995b). It can be expected in BC that each wetland will be considered distinct, and a site-specific cleanup plan will be developed on a site-by-site basis. In general, the riverine, spatially complex wetlands have the finest substrate that is sensitive to trampling during a cleanup; trampling can permanently damage plants, root structure and may push surface oil into the subsurface. Alluvia delta wetlands and lagoon/tidal flat
wetlands may have more coarse sediment and support more traffic. Trampling can be reduced by using boards placed on top of the wetland or by using flat-bottom boats to access the site on a rising tide. Manual and hydraulic cleanup techniques are likely to be the most widely used countermeasures; with vacuuming of pooled oil, raking of oiled debris and low-pressure flushing to remove loose oil being the most commonly used techniques. Cutting of oiled vegetation requires knowledge of the species sensitivity. Burning has been used on some wetland spills but most burning has been conducted on Spartina alterniflora, a species not represented in BC. Decisions about burning will have to be based on specific site conditions and in consultation with wetland ecologists. Non-Spartina burn treatments have shown wetlands to be re-established within 3-15 years after burning. Bioremediation is another cleanup technique that could be applied in BC wetlands, however specific species information about BC plant communities that would respond to this cleanup, or details of species to use as ‘bio-remediators’ is lacking.

Should small areas of wetland have to be removed, there are some examples of small areas of BC wetland restoration. Habitat compensation programs suggest that approximately 5 years or more are required to establish a climax-type wetland vegetation complex.

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