CRITICAL LOADS OF ACID DEPOSITION ON SCOTTISH SOILS

The impact of acid deposition, attributable to sulphur and nitrogen po llutants, on the soils of Scotland has been analysed using a critical loads approach. The critical load of a soil (as an indicator of ecolog ical damage) is calculated from the soil parent material controlling w eathering and soil development. Using existing soil survey information national maps for critical loads of acidity and the sulphur fraction are presented for soils under natural and semi-natural ecosystems. The results show that highly sensitive soils, that is those derived from quartzite and granite are limited in occurrence. However, there are la rge areas of sensitive soils predominantly to the north and west of th e Midland Valley and in the Southern Uplands, in receipt of acid depos ition in excess of their critical load. Enhanced soil acidification sh ould be widespread in these areas and consequently the ecosystems whic h they support will be adversely affected. The least sensitive soils, overlying limestone or marl, are restricted in occurrence and are conf ined to the major deposits of marine alluvium. The results of the anal ysis may be used to help policy makers derive emission abatement strat egies in the context of the European Sulphur protocol renewal in 1993. In Scotland the maps may be used to aid the planning of large scale a fforestation.