Application of the critical loads approach in South Africa

Abstract

South Africa is the most industrialised country in southern Africa and stands at some risk from negative pollution inapa~ To the authors' knowledge, this paper presents the first attempt to apply the critical loads approach on the African corainent; although sensitivity mapping has been performed for Africa and the rest of the world (Kuylerstiema etal, this conference). Actual sulphate and base cation deposition loads in Mpumalanga (formerly the Eastern Transvaal province of South Africa) were mapped from 16 monitoring sites. The region is characterised by long, dry periods with little rain, high evaporation (up to 8 nun per day) and low run-off (15% of MAP). Provisional critical load and exceedance maps were produced for the surface waters using the Steady-State Water Chenfistry Model and the Diatom model. Maps of soil sensitivity to acid deposition, based on bedrock lithology, soil chemical characteristics and land cover, were produced. A weathering rate of 0.39-0.86 keq/ha/year was calculated for the most sensitive sites and taken as the critical load, based on the assumption that the weathering rate represents the buffering ability of the system. The critical loads were contrasted with measures of actual deposition to exanfine potential scenario's for critical load exceedances. Akey factor in refining the sensitivity nmps, and allowing estimation of the critical loads, is the accurate calculation of weathering rates under the warmer and more arid environmontal conditions prevalent in South Africa. In a developing country such as South Africa, where research resources are limited, the critical loads approach is a valuable means of assessing the risk of potential impacts of atmospheric deposition. South Africa is recognised as having comparatively high levels of air pollution emissions, particularly in the Eastern Transvaal Highveld. The total SO2 emission rate for the whole of South Africa is estimated to be 2.9 million tons per annum, of which 1.2 million tons are produced by coal-burning power stations. 75 % of these power stations are located in Mpumalanga (tbmlerly the Eastern Transvaal) (Annegarn et al, 1994; Tyson et al, 1988, Turner, pers. comm.). If the needs of South Africa as a developing nation are considered, the requirements tbr econonfic ~a'ox~N and associated employment, education, housing, and primary health cm'e, greatly overshadow issues relating to air pollution and its impacts. Since the critical loads approach can provide a basis on which cost-effective decisions can be made by regional and national authorities with respect to air quality, its potential use in South Africa was investigated. This paper presents the results of a pilot study to investigate the application of the critical loads approach in South Afi-ica.