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Native plants clean up

There has been a lot of research on using native plants to remove the contaminants from soil and groundwater, and also their use in erosion control on rehabilitation projects. Much of this research is done by mining companies, universities and environmental consultants.

Part of mining today is the clean up and restoration of land. Depending on the type of mining, the land may be restored to previous use (sand mining restores the coastal topography, coal mines restore fertile farmland). Other uses may be recreational such as water – the olympic rowing area in Sydney is an old gravel pit. Some of the problems faced by the mining industry include stockpiles of waste material, toxins such as metals, disrupted regional hydrology (surface and groundwater) or large pits or soil erosion.

Revegetation usually occurs during the mining process. Topsoil (with its reserves of seeds, microbes and fungi) is stockpiled separately and stored to spread over disturbed land. This may be deep ripped to encourage drainage, and a selection of local plants chosen to be seeded or planted. There may be a non native planted as a 'nursery' crop to help protect the soil and plants from erosion.

Companies spend time and money collecting local native seed, studying fertilizer requirements, planting times, water needs, toxin levels and also inoculating soil with the correct nitrogen fixing bacteria. A minimum planting would be 20 species, up to whatever the original diversity- possibly 100's of species over hectares. There are also follow up projects encouraging and monitoring insects and fauna return.

Contaminated land and groundwater (from past industrial use) is another area where plant use is increasing. Plants may be used as a cover over a site, or actually used to remove toxins. For soils, a plants that sucks up metals more than others is known as a hyperacculmulator. Those may be used, or others such as sunflowers and mustard. The plants are harvested with their load of toxins which may be recycled or landfilled.

Groundwater may be cleaned up or stopped from reaching a creek via deep rooted trees such as eucalypts. These intercept and use the contaminated groundwater. The toxins, depending on type, may breakdown or be stored in the tree. Another way is to pump out groundwater or mine drainage water into a constructed wetland. Here plants, bacteria and algae work to breakdown contaminants to harmless forms, while clearing the water.

All these methods are cheaper in terms of money and greenhouse gas generation, although all take more time than conventional, more energy costly treatments.

I shall do some more in depth articles on this topic in the future.

Happy Gardening,

The Potting Bench

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