radicle beets

Wetland Update by radiclebeets
June 12, 2012, 8:40 pm
Filed under: Pod updates | Tags: , ,

We’ve been poking away at our little urban wetland, getting to know the site and developing strategies for its transformation. To date, we have: removed a section of chain link fencing containing it, cut many large Himalayan Blackberry canes to the ground, removed 250 kg of waste from the site, pulled even more waste out of the wetland and piled it on the side of the cul-de-sac, planted a few Hardhack and Snow Berry shrubs, and consulted with local bio-remediation firms and wetland restoration groups (notably Western Seed and Erosion and the BC Wetlands Institute).

We’ve come to realize that completely remediating the soil of all toxins is likely impossible. The proximity of many CN rails with their creosote soaked ties, and the position of our site at a low point directly adjacent, means that the polycyclic aromatic hydrocarbons (PAHs) common in creosote have likely seeped into our wetland. The guide Brownfields to Greenfields: A Field Guide to Phytoremediation says “PAHs are over 100 chemicals, formed during the incomplete burning of many organic substances.” PAHs have been shown to damage red blood cells, leading to anemia. They also suppress the immune system and are known to cause cancer.

There are, luckily, 3 easily grown native plants that will degrade PAHs in the soil. White Clover (Trifolium repens), Tall Fescue (Festuca arundinacea), and Switch Grass (Panicum virgatum) naturally take up and break down PAHs “through the release of enzymes and metabolic processes such as photosynthetic oxidation and reduction. In this process organic pollutants are degraded and incorporated into the plant or broken down in the soil.” Red Mulberry (Morus rubra) and Hybrid Poplar (Populus deltoides x P. Nigra) are also able to phyto-degrade PAHs. We have not received results from soil testing and so are not sure what other contaminants may be in our wetland.

The plan for now is to invigorate the wetland nature of this site, by planting a variety of native plants that like wet conditions. In the coming weeks, we will purchase some plants from local nurseries and acquire many more through respectful seed gathering and division from healthy local wetlands and riparian areas. We will also be laying down a permeable barrier of burlap in an attempt to control the invasive Himalayan Blackberry on site. We hope to cover this layer with an inoculated soil mixture, designed to introduce beneficial bacteria and fungi, to further bio-degrade soil contaminants. We are also going to excavate a small area at the center of the wetland, to expose water for more of the season. We’ve found that in the late spring, water slips just below the soil level. Digging down a foot or two will leave this water exposed to the surface and provide an important water source for native insects and birds.

Here is a partial list of local plants we hope to gather (along with the aforementioned phyto-degraders): Skunk Cabbage (Lysichiton americanum), Cattail (Typha latifolia), Red Osier Dogwood (Cornus stolonifera), Willow (Salix spp.), Hardhack (Spiraea douglasii), Sweet Gale (Myrica gale), Pacific Crab Apple (Malus fusca), Paper Birch (Betula papyrifera), Black Cottonwood (Populus balsamifera), Red Alder (Alnus rubra).


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