«Ecological restoration of land with particular reference to the mining of metals and industrial minerals: A review of theory and practice J.A. Cooke ...»
Ecological restoration of land with
particular reference to the mining
of metals and industrial minerals: A
review of theory and practice
J.A. Cooke and M.S. Johnson
Abstract: Mining causes the destruction of natural ecosystems through removal of soil
and vegetation and burial beneath waste disposal sites. The restoration of mined land in
practice can largely be considered as ecosystem reconstruction — the reestablishment of the
capability of the land to capture and retain fundamental resources. In restoration planning, it is imperative that goals, objectives, and success criteria are clearly established to allow the restoration to be undertaken in a systematic way, while realizing that these may require some modiﬁcation later in light of the direction of the restoration succession. A restoration planning model is presented where the presence or absence of topsoil conserved on the site has been given the status of the primary practical issue for consideration in ecological restoration in mining. Examples and case studies are used to explore the important problems and solutions in the practice of restoration in the mining of metals and minerals. Even though ecological theory lacks general laws with universal applicability at the ecosystem level of organization, ecological knowledge does have high heuristic power and applicability to site-speciﬁc ecological restoration goals. However, monitoring and management are essential, as the uncertainties in restoration planning can never be overcome. The concept of adaptive management and the notion that a restored site be regarded as a long-term experiment is a sensible perspective. Unfortunately, in practice, the lack of post-restoration monitoring and research has meant few opportunities to improve the theory and practice of ecological restoration in mining.
Key words: restoration, rehabilitation, revegetation, mining, succession, ecological theory.
Résumé : L’exploitation minière entraîne la destruction d’écosystèmes naturels par l’élimination du sol et de la végétation et l’établissement de sites d’enfouissement pour les déchets. En pratique, la restauration des terrains miniers peut largement être considérée comme une reconstruction d’écosystème avec la remise en place de la capacité du terrain à capter et à retenir les ressources fondamentales. Dans la planiﬁcation de la restauration, il est impératif que les buts, les objectifs et les critères de succès soient clairement établis pour s’assurer que la restauration soit entreprise de façon systématique, tout en réalisant que ces paramètres peuvent nécessiter quelques modiﬁcations plus tard, à la lumière de la direction dans laquelle la succession de la restauration suit son cours. Les auteurs présentent un modèle de planiﬁcation selon lequel la présence ou l’absence de sol fertile conservé sur le site reçoit le statut de problématique pratique primaire en vue de la restauration Received 22 May 2001. Accepted 22 November 2001. Published on the NRC Research Press Web site at http://er.nrc.ca/ on 11 March 2002.
J.A. Cooke.1 School of Life and Environmental Sciences, University of Natal, Durban, 4041, South Africa M.S. Johnson. School of Biological Sciences, University of Liverpool, Liverpool L6972B, U.K.
1 Corresponding author (email: email@example.com).
Environ. Rev. 10: 41–71 (2002) DOI: 10.1139/A01-014 © 2002 NRC Canada 42 Environ. Rev. Vol. 10, 2002 écologique des terrains miniers. Ils utilisent des exemples et des études de cas pour explorer des problèmes importants ainsi que des solutions pour la pratique de la restauration liée à l’exploitation des métaux et minéraux. Bien que la théorie écologique manque de lois générales avec des applications universelles au niveau d’organisation de l’écosystème, la connaissance écologique a un grand potentiel heuristique et une forte applicabilité pour des objectifs de restauration écologique sur des sites spéciﬁques. Cependant, le suivi et l’am énagement sont essentiels, puisque les incertitudes dans la paniﬁcation de la restauration ne peuvent jamais être totalement surmontées. Le concept d’aménagement adaptatif avec la notion qu’un site restauré doive être considéré comme une expérimentation à long terme est une perspective raisonnable. Malheureusement, en pratique, le manque de suivi et de recherche post-restauration offre peu d’occasions d’améliorer la théorie et la pratique de la restauration des terrains miniers.
Mots clés : restauration, réhabilitation, végétalisation, exploitation minière, succession, théorie écologique.
Introduction The scale of human activities has become such that most of the ecosystems of the earth have been disturbed in some way (Ehrlich 1993). More than 40% of the terrestrial vegetated surface of the earth has been directly disturbed (Daily 1995) and its natural productive capacity diverted, reduced, or destroyed (Vitousek et al. 1986). This is largely through overgrazing, deforestation, agriculture, overexploitation for fuelwood, and urban and industrial use (Daily 1995). The area of land directly altered by mining industries is still relatively low in terms of the global inventory of degradation, but can represent considerable quantities on an individual country basis. Examples of estimates on a country basis include, for the U.S.A. 3.7 Mha (Dudka and Adriano 1997), for China 2 Mha (Guo et al. 1989), and for South Africa about 0.2 Mha (Fairbanks et al. 2000). Further, the scale of mining is increasing and the impacts are generally more severe than most other kinds of disturbance (Walker and Willig 1999). In this context of increasing land degradation, both the ecological and economic imperatives demand that restoration of land be prioritized even if restoration ecologists are “doomed to ﬁght an uphill battle” (Ehrlich 1993).
This review discusses some of the main issues, both theoretical and practical, concerning ecological restoration of land in the particular context of metal and industrial mineral mining.
The mining context The focus of this review is the mining industries, whose products are the metals and minerals on which many national economies depend (Table 1). There has been a progressive increase in the production of most of these metals and minerals over the last 50 years (Table 2). The mining of metals and minerals represents a large range of activities, which include primary (extraction) and secondary (milling, processing, reﬁning, and waste disposal) phases (Barbour 1994). Table 3 summarizes the main methods of underground or surface extraction and the nature of the associated land disturbances. In many of the forms of mining it is the waste production and disposal that can cause the most extensive and long-lasting disturbance to land. The disposal of rock and overburden, the construction of impoundments (dams) for the ﬁne tailings (0.1 mm) produced from the milling operations, and the disposal of slags from the smelting and reﬁning stages can involve large areas of land.
The history of modern mining is one of globalization (Mining Annual Review 1995), together with the economic development of lower grade ore bodies with larger mines, increased waste production and consequently greater potential environmental impacts, and land disturbance. The history of modern copper production illustrates this (Mining Annual Review 1985), where the average ore grade has decreased from 4% in 1900 to 0.5% in 1975, with a considerable increase in the tailings produced, going from approximately 17 to 290 Mt a−1 worldwide over the same period (Williamson et al. 1982).
In terms of land disturbance this can translate into the production of both massive open pit workings (e.g., 3 km wide and 0.5 km deep) and individual tailings dams of over 2000 ha.
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The direct impacts of mining disturbance to land surfaces are usually severe with the destruction of natural ecosystems, either through the removal of all previous soils, plants, and animals or their burial beneath waste disposal facilities. Phosphate mining on the small Paciﬁc island of Nauru provides an example of both severe mining disturbance, with 80% of the islands soil and vegetation lost, and extreme ecological restoration challenges (Anderson 1992; Gowdy and McDaniel 1999). Structural faults and major failures of mining waste impoundments have caused gross pollution of the wider environment and threatened agricultural and sensitive natural ecosystems. For example, the Ok Tedi gold and copper mine in Papua, New Guinea, discharged 60 Mt of tailings per year into the Fly river and the Gulf of Papua over many years from an original dam failure in 1984 (Allan 1995; Anderson 1996), and the Los Frailes open-pit pyrite mine in southern Spain released 4.5 x 106 m3 of acidic and metalliferous slurry into the Agrio and Guadiamar rivers, which covered some 4000 ha of land and threatened the largest conservation area in Europe, the Doñana National Park (Sassoon 1998; Cabrara et al. 1999).
Further widespread geographical impacts are possible through the pollution of air (e.g., sulphur dioxide and metals, including mercury (Hutchinson and Whitby 1974; Ripley et al. 1996; Dudka and Adriano 1997; He et al. 1998)), surface waters (e.g., acid mine drainage (Ferguson and Erickson 1988), mercury (Veiga and Meech 1995)), and ground water (Sengupta 1993). Other indirect or multiplier effects can ©2002 NRC Canada 44 Environ. Rev. Vol. 10, 2002
occur through the fragmentation of the original natural ecosystems and the alteration of surface and groundwater drainage patterns.
There is also a probability of recurrence of impacts after mining (even after site reclamation) where mining wastes are regarded as secondary ore bodies, and old spoil heaps and tailings dams are reworked for metals and gangue minerals. The recent accident at the Aural gold and silver producing plant at Baia Mare in Romania clearly showed the environmental consequences of reprocessing wastes activities when 50–100 t of cyanide were released into the Danube river system. The cyanide plume travelled to the Black Sea some 2000 km from the source of the spill, causing mortality of river biota (UNEP/OCHA 2000).
Mining is a temporary landuse because, in any one place, the mineral deposit is ﬁnite and eventually exhausted. The social and legislative context of mining in many parts of the world today means that some form of landuse goals will be set prior to the granting of planning permission for a new mine. Reclamation considerations will be incorporated into the mine planning such that it becomes a major governing factor in the mining operations, waste disposal, and site closure (Johnson et al. 1994). However, it should be emphasized that there is a considerable past legacy of poor reclamation practice that, at best, has not provided any successful ecosystem development and, at worse, has allowed continual environmental damage (Berger 1990). It may be concluded that it is the reclaimed land surface that remains indeﬁnitely and is required to meet the major goal of sustainability, which is the maintenance of the land use options of future generations (Haigh 1993). In this context, ecological restoration of mined land represents the best approach to promote both sustainability and the maintenance of biodiversity.
reclamation describes the general process whereby the land surface is returned to some form of beneﬁcial use. Where reclamation is guided by ecological principles and promotes the recovery of ecological integrity (SER 1996) the term restoration is used.
A more detailed set of deﬁnitions has been proposed to reﬂect the goals (or success?) of the reclamation process. Here, restoration refers to reinstatement of the original (pre-mining) ecosystem in all its structural and functional aspects, rehabilitation is the term used for the progression towards the reinstatement of the original ecosystem, and replacement is the creation of an alternative ecosystem to the original (Bradshaw 1984, 1990). It is likely, given the nature of the science of ecology, that these deﬁnitions make the use of the word “restoration” redundant and only used by the optimistic or naive ecologist. Obvious caution, when dealing with the restoration of complex ecosystems, may lead to the overuse of the word “rehabilitation” in ofﬁcial documents such as Environmental Impact Assessments of proposed mining operations (e.g., Lubke et al. 1993). In practice, the terms are still used interchangeably and restoration, rehabilitation, and replacement (or habitat creation in a nature conservation context (Anderson 1995)) may be described as the resetting of an ecological clock (Cairns 1991). All of these terms are included in the one general term restoration in this review, and this reﬂects both the earlier literature (e.g., Johnson and Bradshaw 1979) and recent discussions of the topic (e.g. Wyant et al. 1995;
Hobbs and Norton 1996; Pastorok et al. 1997).
As well as accepting the broader view of ecological restoration, it should be emphasized that it is a “process”, driven by ecological knowledge and research and not just the means of producing a “product”, e.g., the (fully?) restored pre-mining ecosystem. From this perspective ecological restoration is about a broad set of activities (enhancing, repairing, or reconstructing degraded ecosystems (Fig. 1)) appropriate to the speciﬁc types (or severity) of disturbances and not the outcomes per se of such activities (Hobbs and Hopkins 1990; Cairns 1991; Hobbs and Norton 1996). Within this broad overview of restoration activities, the restoration of mined land can largely be considered as ecosystem reconstruction. Here it is usually a question of the re-establishment of the capability of the land to capture and retain fundamental resources (energy, water, nutrients, and species). In nearly all cases, the resilience of the pre-mining ecosystem has been compromised (more precisely the amplitude of the system has been exceeded (Westman 1991)) and the recovery process, when left to natural succession, is often too slow (Bradshaw 1990; Hobbs and Norton 1996).
This view of restoration as a process is regarded as more appropriate to current thinking of succession: