6.4.1 Conservation of Flora and Fauna in Restricted Areas
Impact: The most notable positive impact on the biophysical environment comes from the de facto nature reserve status of much of the terrestrial mining area. Access to most mining areas is highly restricted in order to minimise diamond theft, and as a consequence, human interference in many areas has been kept to a minimum. Many habitats have been left in pristine or near pristine condition, the scale of which is not insignificant - the Namibian ‘Sperrgebiet,’ for example, alone encompasses some 26 000 km2 of land.
The positive benefits from diamond mining are unequally shared between the marine and terrestrial environments, however. While access is restricted on land, large-scale offshore fishing enterprises continue uninterrupted along much of the diamond coast. Only shore-based forms of exploitation are effectively excluded.
6.5 Biophysical Environment - Negative Impacts
Considered as a whole, marine diamond mining affects only a small fraction of the marine environment (Table 3). The overall aerial extent of mining activities encompasses less than 1% of the concession areas in South Africa and Namibia per annum, irrespective of the form of mining category. On the scale of the BCLME therefore, impacts of diamond mining are deemed to be of low to negligible significance. At local scales, however, their impact may be more severe. Due consideration must be given to the scale of operations when the impacts outlined below are evaluated.
Table 3. Relative extent of the various diamond mining activities in South Africa and Namibia.
Impact: The impacts of terrestrial mining are caused individually or in synergy from 10 categories of mining activity: prospecting trenches; overburden dumps; tailings dumps; mining blocks; sediment plumes; roads and vehicle tracks; scarring and quarries; mining infrastructure; seaward disposal of fines tailings; and beach mining. Perhaps the three greatest impacts from terrestrial mining are due to the removal of overburden and diamondiferous gravel, the creation of overburden and tailings dumps, and the construction of roads. These activities impact soils and plant communities, in turn impacting the animal communities associated with them. The degree of impact depends on both the scale of the mining activity and the type of soil that is impacted. Actively forming soils harbour plant communities that are dynamic and resilient to even massive disturbances, whereas plant communities growing on older complex soils are dependent on the equilibrium of the soil, and usually fail to recover from disturbance if this equilibrium is not maintained. Stripping of overburden with a complex topsoil therefore has a relatively greater impact of longer duration than stripping an area of actively forming soils. Although some areas are back-filled, topsoils are generally not stored and the loss of topsoil means that recovery of plant comminutes to their former state depends on the formation of new soils – in the order of decades to centuries. Loss and recovery of animal fauna presumably follows the same route. Roads and heavy vehicle movement has the opposite effect to mining. These activities tend to compact the soil, thus rendering the area unsuitable for re-colonization by new plants. Additionally, it should be noted that numerous rare, threatened or endemic animal and plant species occur in the diamond areas, and are negatively affected by mining activities.
Areas denuded of vegetation, such as trenches, mining blocks and tailings are inherently unstable, with the result that sand plumes frequently develop due to the strong winds and flat topography characteristic of the mining area. These sand plumes can be quite extensive, smothering vegetation and causing a significant secondary impact. It is believed that sediment plumes may have been a triggering force in the collapse of the saltmarsh ecosystems of the Orange River wetlands.
Additional, lesser impacts are caused by mining infrastructure as buildings and equipment are often left on site following completion of mining, or if the equipment becomes derelict. Not only does this hinder recovery of the ecosystem, it also causes an aesthetic impact, in addition to the mine dumps and trenches that now dominate in a previously flat landscape.
Mitigation: Mitigation is principally through rehabilitation of the affected areas. The severe disturbance that results from mining in these arid terrestrial ecosystems, the dynamics of which are greatly retarded by the harsh environment, makes rehabilitation very difficult, however. Generally larger mining companies make the effort to stockpile topsoil and overburden separately and replace this material in appropriate positions in the refilled mining blocks. Little or no effort is made to rehabilitate prospecting trenches, however.
Seaward Disposal of Fine Tailings
Impact: Discharging fine tailings to sea impacts the intertidal region, whether at a large scale such as the Elizabeth Bay Mine (Namibia) or at a smaller scale such as small contractors operating from the shore.
The sediment plume generated from the seaward disposal of fine tailings impacts intertidal rocky shores. The impact is localised to the extent of the sediment plume – a scale of 100 m in the case of large recovery plants, and a scale of 10 m for the smaller operations. The impact is caused by sand inundation that appears to impact particularly the grazers in the intertidal zone (e.g. Patella granatina, P. argenvillei), causing a decrease in the ability of these animals to adhere to the substrate. The resultant reduction in herbivory often leads to an increase in foliose algal cover, which causes shading and in turn decreases corralline algae cover below. A cascade effect is the loss of food to seabirds that forage on the intertidal. At small-scale contractor mining sites, full recovery takes less than two years after the cessation of mining activity.
Subtidal rocky shores do not appear to be adversely affected by light siltation by mine tailings, with the possible exception of sponges which are particularly sensitive to sand inundation. Should a beach prograde to cover the reef however, complete loss of habitat with the associated communities, will ensue.
The seaward pumping of fine tailings on sandy shores can have a profound effect on communities associated with these habitats. Fine fractions of tailings are suspended in the sea and advected offshore, whereas coarser fractions settle rapidly onto the beach. If large volumes of tailings are pumped seaward, this can lead to severe alterations of the physical state of the affected beach. For example, fine tailings at Elizabeth Bay have increased the size composition of sand across the entire beach. Prior to mining, Elizabeth Bay beach was composed of fine to very fine sands, with sand particles coarser than 100m making up less than 10% of the total amount. With the advent of mining in 1991, mean particle size at the centre of the beach where tailings are disposed has increased from 110-160 m to 600-900 m, with a accompanying reduction of surf zone width by ~50% and an increase in the beach slope from 1:40 to 1:14. Beach macrofauna communities are almost entirely determined by the physical state of the beach, and this alteration to the physical state of the beach has led to a shift from a mussel dominated community to a community dominated by crustaceans with an accompanying loss of diversity. Following mine closure, recovery of the affected beaches to a pristine state will depend on the speed at which the beach returns to pre-mining physical conditions. This could take decades or even centuries.
Fish appear to benefit from the turbidity plume produced by the discharge of tailings spoil material from the Elizabeth Bay diamond mine, with increased species richness and abundance recorded within the plume relative to control sites on the same beach. It is believed that this is attributable to increased shelter from predators provided by the plume. Loss of potential food items (beach macrofauna discussed above), reduction of habitat through the narrowing of the surf zone, and the development of more turbulent waters associated with a narrower surf zone must have some, though unquantified, negative effects.
Mitigation: Terrestrial slime dumps are an alternative to the seaward disposal of tailings, but this option is not without its own impact on the environment. No other mitigation or rehabilitation options are considered economically feasible.