Monitoring ecological rehabilitation on a coastal mineral sands mine in Namaqualand, South Africa

[摘要] ENGLISH ABSTRACT: The Exxaro Namakwa Sands heavy mineral sands mine at Brand-se-Baai, on the west coast ofSouth Africa, is an important source of income, development and job-creation in the region.However, this comes at a great environmental cost, as strip mining causes large scale destructionof ecosystems through the complete removal of vegetation and topsoil. This is particularlyproblematic in an environment, such as Namaqualand, where the arid and windy climate, as wellas saline and nutrient-poor soils, hamper rehabilitation. These environmental constraints createthe need to develop a site-specific rehabilitation program. At Namakwa Sands the objective ofrehabilitation is to 'rehabilitate and re-vegetate disturbed areas and establish a self-sustainingStrandveld vegetation cover in order to control dust generation, control wind and water erosion, aswell as restore land capability. In general, vegetation will be rehabilitated to a minimum grazingstandard capable of supporting small stock (sheep) grazing. In order to achieve this NamakwaSands conducted rehabilitation experiments with topsoil replacement, seeding of indigenousspecies and translocation of mature plants.Monitoring is an important part of the rehabilitation process as it allows rehabilitation practitionersto evaluate success and to adapt their management strategies and rehabilitation methods, as wellas to evaluate and, if necessary, change their rehabilitation objectives. This study forms part of themonitoring process at Namakwa Sands. It assesses the success of sites that were experimentallyrehabilitated in 2001 and a site that was rehabilitated in 2008, using current practice, in order toidentify possible management requirements on rehabilitated sites as well as improvements onrehabilitation objectives, methods and monitoring. This study also tests the Landscape FunctionAnalysis (LFA) as rehabilitation monitoring tool by correlating LFA indices with traditionalmeasurements of biophysical variables or their surrogates.Results showed that experimental sites were not successful in returning vegetation cover and plantspecies richness to the required levels, but did achieve the grazing capacity objective. These siteswill need adaptive management to achieve the vegetation cover and plant species richnessobjectives. The recently rehabilitated site achieved the three-year vegetation cover and plantspecies richness objectives, as well as the grazing capacity objective, within two years afterrehabilitation. Namakwa Sands should therefore continue using the current rehabilitation method.However, rehabilitation should be done in multiple stages in future to decrease the mortality ofnursery cuttings and to facilitate the return of late successional species to rehabilitated sites. The sustainability of small stock farming on rangeland with the grazing capacity that is identified as theminimum objective is questionable and this merits further investigation. LFA can be a useful tool tomonitor nutrient cycling and soil stability at Namakwa Sands, provided that enough replicates areused. However, LFA cannot be used as is to assess water infiltration at Namakwa Sands, due toassumptions in the calculation of this index that do not hold for the Namaqualand environment.Landscape functioning should be monitored annually to complement vegetation surveys.

[发布机构] Stellenbosch University