The Sustainable Management of Metal-Rich Ecosystems: Lessons from an Historic Mining Area

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In the absence of human intervention the ecosystem that develops on an historic mining site adapts to tolerate the particular set of environmental conditions that the mining activity has created. Often this naturally developed ecosystem is of high biodiversity value because only a particular assemblage of organisms can survive on such a stressed site. Stresses may be due not just to high concentrations of metals but may also be physical and biological. The understanding of how metal-enriched ecosystems function can aid the development of sustainable restoration schemes that require minimal long-term management. Three types of metal-rich ecosystems were studied in order to assess processes that lead to natural vegetation establishment and to gain an understanding of the dynamics of the geochemistry of such sites. Their biodiversity value was assessed and processes that lead towards stability were established. The results suggest that it is possible to enhance or encourage natural processes in order to speed up natural recolonisation on metal-rich sites. Historic mining sites have developed diverse ecosystems of high biodiversity value. These include freshwater and saline wetlands and heathlands. These stable ecosystems reduce metal mobilisation. In these studies enhanced growth of vegetation is shown on a prospective heathland site (Table 1) in the presence of various soil amendments. Management of hydrological regimes in freshwater wetlands reduces the risks of metal mobility and high organic material appears to encourage rapid diagenesis and sequestration of metal sulphides. In salt marshes metals become sequestered in plants and then in the reducing zone when plant material is deposited. These results suggest that mine restoration schemes that lead to the development of more ‘natural’ ecosystems will be more sustainable in the long-term and will be simpler to manage than more ‘artificial’ schemes.

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