Ecology and the problems of rehabilitating wastes from mineral extraction

Abstract

Abstract With the growing demand for minerals in the United Kingdom, it is likely that there will be a marked increase in the area of land affected by deep and surface mining and associated industries, e. g. ore-concentration plant, smelters. Thus, in future, in a densely populated, highly industrialized country like the United Kingdom, the economic benefits of working minerals wherever they are found will have to be more carefully weighed against the economic and social costs of temporary or permanent disruption of urban, agricultural or amenity land. Improving our technical knowledge of how to revegetate inexpensively, land disturbed by mining helps to ensure that mineral extraction is not inhibited by nor necessarily inhibitory to other valid uses for land. Environmental problems which may be associated with mineral extraction are: (a) the visual ugliness of open pits, waste tips, and working mess; (b) the nuisance of wind- and water-borne dusts; (c) the health hazards to wildlife, crops, livestock and man of locally increased environmental burdens of potentially toxic metals (e. g. Pb, Cd, As, Zn, Cu, Ni) derived from wind- and water-borne mine dusts and smelter smokes; (d) the safety hazards of surface subsidence and tip-slippage from deep-mining. All these disamenities can be cured or reduced by the reclamation process which involves a blend of socio-economic, legal, planning, civil engineering and biological expertise devoted to development planning, site purchase, land clearance, land forming, stabilization, drainage and revegetation of the affected site. Revegetation is the least well understood of these procedures, but nevertheless an important component because experienced planners have found in practice that revegetation appears to restore to a derelict or disturbed site the greatest flexibility of potential re-use for the widest range of subsequent developments. Traditionally, three approaches to revegetation appear to have been used: (a) accept site conditions as they are, and plant with species known to tolerate harsh conditions, e. g. ecological ‘pioneer’ species; (b) improve the spoil as a medium for plant-growth by incorporating, for example, NPK-fertilizer, lime and organic matter; (c) use geological knowledge to pre-plan excavations so that toxic wastes are buried below the rooting zone. A combination of all three seems most desirable and involves careful species selection together with predictive physicochemical analysis of those site conditions which may inhibit plant-growth. Because our knowledge in these two areas is deficient, it is at present necessary in most cases to use heavy applications of topsoil as a blanket to isolate the growth inhibitory properties of the spoil. A sum equivalent to probably 1% of the current reclamation costs using soil is being spent on research into ways of doing without topsoil although the limited research which has been done has proved very successful on a small scale and it likely to be equally successful on a wider scale if adequately supported. A better understanding of site factors which inhibit establishment of plants is urgently required because this will enable the reclaiming agency to predict the existence of special site problems and thus avoid expensive failures. Valuable lessons can be learned from the ways in which common inhibitory factors interact in various combinations on the following spoils and waste-substrates from mineral extractive and other industrial activities: smelter slags and wastes; chemical wastes; coal wastes; pulverized fuel ash; metal mine wastes; brick-clay pits; slate and shale wastes; stripped peat land, quarry stone pits and wastes; china-clay pits and wastes; sand and gravel workings; ironstone wastes; domestic refuse. The most important environmental inhibitors are; instability; spontaneous combustion; unworkably steep slopes, poor water régime (floods and droughts); high levels of toxic elements; cementation and compaction; temperature extremes; ‘wind-rock’ and ‘sand-blasting’ effects; low nutrient status; excessive stoniness (no fine ‘soil’); broken uneven surfaces (no seed bed); water erosion; no soil micro-organisms and soil fauna. Although a knowledge of these will assist in establishing vegetation, time and money must be spent on maintaining the planting for a few years until, ideally, it can be almost self-perpetuating. This vital need in revegetation practice is least understood, usually remains unrecognized and is often not budgeted for. Five important needs thus emerge for promoting a better understanding of how to revegetate inexpensively and successfully a wide range of mineral extraction sites: (1) One or two U. K. plant materials centres for screening potential reclamation species, as is done in U. S. A. and Denmark. (2) Further research at ‘laboratory’, ‘glasshouse’ and ‘field-trial’ levels on ways of revegetating without using topsoil. (3) Studies on maintenance and management problems. (4) A small advisory capability to translate these research findings into practical recipes for action. (5) A small levy which is collected by law from the operator on each tonne of material disturbed, i. e. similar to the Ironstone Restoration Fund. This would be devoted to reclamation costs.

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