Characteristics Of Acid Deposition And Environmental Effects Of Typical Acid Rain Areas In Southern China

Within the20th century the energy structure produced significant changes worldwide. But in China the dominant energy structure as coal in the near future will not be substantially changed. The growth of coal usage and the increase of auto ownership brought gradual increase of main gases emissions of acid subsidence (SO2, NOx). Acidic substances (gases or aerosols) by the way of dry and wet deposition fell upon the ground, which not only brings huge economic losses, but also devastatingly attacks the ecosystems. Acid subsidence has become one of the biggest environmental problems in the21st century. This article established three acid rain observation sites with high international standards in the typical acid rain area in China. The observation sites are Tieshanping in Chongqing Province, Caijiatang in Hunan Province and Leigongshan in Guizhou Province. We used the taking sample and chemical analysis method recommended by EMEP monitoring network to study acid subsidence systematically, the results are as follows:The study areas mentioned above are the typical forest watershed (2001-2004). Acidity materials in dry deposition mainly were SO2, SO42-and NO2. Alkaline substances with seasonal changing characteristics (pollution in spring and winter were much serious) mainly are Ca2+, NH4+K+and NH3. Atmospheric precipitation all appeared serious acidification, the order of average pH were:TieShanPing (4.12)<CaiJiatang (4.62)<LeiGongshan(4.96). Main anion in atmospheric precipitation and the throughfall forest was SO42-while the main cation was NH4+for CaiJiatang and TieShanPing. But for LeiGongshan, the main anion was Cl-and the main cation was NH4+in atmospheric precipitation, while the main anion is SO42-and the main cation was K+in forest throughfall. In addition, various ionic components appeared concentration in different degrees in forest throughfall, where the total ion was increased by2.75,1.79and4.63times in Caijiatang, Leigongshan and Tieshanping, respectively.Atmospheric precipitation had taken deeply ion exchange reaction when it penetrated through vegetation canopy which caused a significantly increase of pH value. In the condition of perennial acid subsidence in Shaoshan region, the layers of canopy can absorb SO42-, NO3-, Mg2+, NH4+and Na+. Absorption to SO42-and NO3-was the most pronounced. The canopy eluviations percentages of SO42-, Ca2+and Mg2+obviously reduced with the increase of precipitation. The canopy eluviations percentages of Ca2+, K+and Cl-showed the tendency to increase with pH. The sequence of ion leaching through forest canopy in Shaoshan was K+> Ca2+> Cl-> Mg2+> SO42-> NO3-> NH4+> Na+The nitrogen and sulphur concentrations in precipitation in Shaoshan CaiJiatang watershed from2001to2003were negatively correlated with rainfall while the output concentrations were positively correlated with surface runoff. The inputs of total nitrogen gave priority to NH4+. The forest nitrogen deposition is close to the Europe’s biggest penetrate value of25kg/(hm2.a) for nitrogen deposition, The output flux was mainly affected by rainfall and surface runoff, and the substantial output of NO3-had not appeared, which was due to that most of the output were intercepted by ecosystem. The input flux of SO42-was significantly higher than its output flux which maintained a higher amount of the net interception.The mechanism of SMART model is similar to the MAGIC model. In light of complement to the two models, the combination model of MAGIC and SMART was used. Acid deposition critical load calculated by the combination model was much closer to the measured value in comparison with SMART, result showed a critical load of sulfur subsidence in Shaoshan was1.76keq/(hm2.a).Soil acidification in the study area was relatively serious. The acidification degree was Tieshanping> Caijiatang>Leigongshan. The soil systems in Caijiatang and Leigongshan area had relatively larger buffer capacity to acid subsidence, while the buffer capacity in Tieshanping region had close to its saturation. The deposition of Nitrogen and sulfur largely accelerated the process of soil acidification, and in which the H+flux generated by nitrogen deposition was more than that of sulfur. Because of the plentiful existence of activity calcium in soil, the higher Ca/Al ratio could be maintained and the acid deposition did not showed aluminum poison effect obviously.