Acid rain and acidification in China: the importance of base cation deposition

Acid deposition has been recognized as a serious environmental problem in C hina. Most acid deposition studies have focused on sulfur deposition and th e pH of precipitation. However, as high concentration of alkaline dust is a n important feature of the atmosphere in large parts of China, base cation deposition must be taken into account when discussing possible effects on s oils and vegetation from acid deposition. We estimate the deposition of sul fur as well as calcium, i.e. the dominating anion and cation, on a regional scale in China using data both from measurements and modeling. The ratio o f sulfur/calcium in deposition is then used as an indicator for identifying areas where deposition acidity exceeds alkalinity, and where soils may be at risk to acidification. The dynamic soil acidification model MAGIC is app lied with data from two sites receiving high deposition loads in southwest China. The model predictions indicate that considerable soil acidification has been going on for the last decades due to acid deposition inputs. Effec ts on the spatial distribution of acidic deposition in China, using differe nt future deposition scenarios, are illustrated. As the size of the anthrop ogenic fraction of the base cation deposition is unknown, different possibl e future trends in calcium deposition were used. Soil response, according t o the model, using different combinations of sulfur and calcium deposition scenarios is shown. Applying the most strict measures to reduce sulfur emis sion will almost eliminate the acid deposition problem; however, such a sce nario is not economically feasible in the short term. A strict, but possibl y realistic, future scenario for sulfur may be enough to keep the situation at the present level, assuming only moderate reductions in calcium deposit ion. With large decreases in base cation deposition, increased soil acidifi cation can be expected even with considerable sulfur emission reductions. ( C) 2000 Elsevier Science Ltd. All rights reserved.