Creation of New Alternative Ecosystems

Newly created ecosystems, not necessarily resembling what was present prior to mining, may be of equal or even greater value. Of course, what determines the value of an ecosystem is a matter of debate, but for argument's sake let us assume here that, at the same place and time, the value of an ecosystem increases with increasing bio diversity. While mining typically reduces biodiversity, there is at least one example where the opposite occurred. The zinc violet, V. calaminaria, is abundant in the lead-zinc mining district around the town of Plombieres in the northeast of Belgium. It probably was restricted originally to natural outcroppings of zinc-lead ores, but is now widespread in the area due to past mining activities. A small river, the Geul, flows through the area, north wards across the nearby border of the southernmost part of The Netherlands. Zinc carried with sediments from the area around Plombieres was deposited along the Geul floodplains and this led to enhanced concentrations of zinc in the sediments. Due to the mining activities, the zinc violet and a few other metallophytes spread north wards along the Geul. Because the local geology consists of limestone, acidity often associated with mines was not a problem and the grasslands in the area are known for their species richness. The addition of the zinc violet and other so called 'zinc flora' increased rather than decreased the biodiversity. This led to the interesting situation that, even though the plant species belonging to the 'zinc flora' are abundant across the border in Belgium, in The Netherlands it is only found along very short stretch, less than a few kilometers, of the Geul River, which therefore is a protected nature reserve. Because the mining activ ities ceased decades ago, the zinc concentrations in the Geul sediments are slowly but surely decreasing. As a result, the zinc violet is becoming increasingly rare. It has even been suggested that zinc should be added to the soils to ensure that V. calaminaria remains part of the Dutch flora!

Apart from the example above, mining activities usually lead to decreased biodiversity, but this does not mean that the newly created habitats are necessarily less valuable from an ecological point of view - these new habitats may become home to species that have seen their habitats destroyed elsewhere. An example is the recent expansion of the eagle owl (Bubo bubo) in Europe. This bird of prey requires rock faces for nesting and it appears to be benefit ing from the creation of such habitat in mine quarries. In addition, as the example of the zinc violet shows, habitats created anew due to mining may attract highly specialized species that otherwise would not occur in the area. 'Remediation' of such sites might in fact destroy valuable habitat! However, remediation is certainly necessary where the benefits of newly created habitats are outweighed by the damage done to other, surrounding habitats, for exam ple, due to acid mine drainage, leaching of toxic metals into surface and groundwater, etc.

Under such conditions too, creation ofnew ecosystems not resembling those present prior to mining can be very effective. Again we can learn from naturally developing ecosystems in mining impacted areas. While metallo phytes may colonize dry habitats associated with mining, quarry lakes and tailings stored under water may support wetland habitat. These wetlands display a wide range of chemical conditions, yet often support vegetation. In fact, it has only been realized recently that many wetland plants have constitutive tolerance to metals. This, together with the fact that a water cover prevents dust blows and provides biogeochemical condi tions that render most metals immobile, has made wetlands particularly popular for remediation of mine tailings that are high in metal concentrations.

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