Study On Mapping Critical Loads Of Acid Deposition In China

To meet the requirement of acid deposition control in China, critical loads of acid deposition (include sulfur and nitrogen) were mapped through the steady state mass balance (SSMB) method. The weathering rates of Chinese soils necessary for applying SSMB were derived based on the experimental measurement and theoretical calculation. Result shows that the weathering rates were very low (usually lower than 1.0 keq·ha^-1·a^-1) for allite in south China and silalsol in northeast China, but very high for xerosol and alpine soil in northwest China. The growth uptakes of nitrogen and base cations, another two important parameters, were also derived by multiplying the annual increases in biomass by the element contents of the vegetation. Supported by a geographical information system (GIS), critical load maps of acidity, sulfur and nitrogen of China were compiled with resolutions both of 0.1° (latitude) × 0.1° (longitude) and 1° × 1°. As can be seen from the critical load map of acidity, the lowest critical loads (< 0.2 keq·ha^-1·a^-1) occurred on the Daxingan Mountain and the Sanjiang Plain in northeast China, then followed by the Xiaoxingan Mountain and the Changbai Mountain in northeast China, the valley of the Yaluzangbu River on the south of the Tibetan Plateau, the catchments of the Nu River and the Lancang River in the southwest of Yunan province, Leizhou Peninsula, and the west of Hainan Island. The critical loads of Ferralsol areas in south China, where acid deposition is very high, were intermediate and in the range of 0.5².0 keq·ha^-1·a^-1. Therefore, according to the critical loads of acidity, China might be divide into two parts approximately by the 400mm isohyet - the northwest part could generally tolerate more than 2.0 keq·ha^-1·a^-1 acid deposition, but the southeast one could not. Similar to the distribution of the critical loads of acidity, the critical loads of sulfur were high in west China and low in east China. However, the critical loads of nitrogen were low in the west and high in the east. The lowest critical loads of nitrogen (<1.0 g·m^-2·a^-1) occurred on the west of the Tibetan Plateau and on the Alashan Plateau, and the highest (> 4.0 g·m^-2·a^-1) on the Dongbei Plain, the Huabei Plain, the Changjiangzhongxiayou Plain, and the Sichuan Basin, etc. Among all ecosystems, coniferous forests, steppes and deserts were more sensitive to nitrogen deposition than broad-leaf forests, shrubs and meadows. Based on the critical loads of both sulfur and nitrogen, China might be divided into seven regions. The priority of sulfur or nitrogen to be controlled is different in these regions.