Critical loads of acidity for surface waters in China

For further control of acid rain and sulphur dioxide pollution, the Chinese government has designated the Acid Rain Control Zone and the Sulphur Dioxi de Pollution Control Zone for those areas that are, or could become, affect ed by acid deposition or ambient sulphur dioxide concentrations. One of the most important principles for designating the Acid Rain Control Zone is th at the critical load is exceeded by the sulphur deposition. Through the ste ady-state water chemistry method (SSWC), critical loads of acidity for surf ace waters were mapped based on available data. Results show that surface w aters sensitive to acid deposition, i.e. surface waters with low critical l oads, are mainly found in north-east China, on the Tibetan Plateau, and in north-west China. Compared with the critical loads of soils, critical loads of surface waters are usually higher in almost all areas in China. The rea son for very low critical loads of surface waters in some regions dominated by soils geologically not sensitive to acid deposition may be attributed t o the low temperature, high altitude and low runoff. In contrast, surface w aters in south China are not susceptible to acid deposition, and so far aci dification of surface water has not been found in spite of the heavy acid r ain. As can be seen from the critical load exceedance map, nearly 10% of th e surface waters are subject to risk of acidification in 1995. (C) 2000 Els evier Science B.V. All rights reserved.