YAN Zelong1, HAN Xiaokun1, YUE Fujun1,2,3, ZHONG Jun1, WANG Zhongjun2,3, ZENG Jie2,3, LI Siliang1
(1 Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, China;
2 Institute of Geochemistry, Chinese Academy of Sciences, Guiyang Guizhou 550002, China;
3 Puding Karst Ecosystem Observation and Research Station, Chinese Academy of Sciences, Puding Guizhou 562100, China)
Abstract: The acid rain is common in southwest China. Samples of rainwater were collected in the Puding Karst Ecosystem Observation and Research Station, Chinese Academy of Sciences, during the period of from May 2016 to September 2017 and their chemistry and sulfur isotope compositions were measured in order to understanding the variation tendency and formation mechanism of acid rain in the karst agricultural area of southwest China. The results showed that 71.0% of precipitations in the study area were not acid rain (pH>5.6), SO42- and Ca2+ were predominant ions in rainwater, accounting for 78.1% of total anion and 56.6% of total cation contents, respectively. The weighted mean sulfate concentration (98.9 μmol/L) of rainwater samples was significantly lower compared with that (140.6 μmol/L) in the year 2008. The sulfur isotopic compositions of sulfate in precipitations ranged from -6.5‰ to 21.2‰ and the weighted mean was 1.3±6.2‰ and larger than that in Guiyang during years 2008-2009 (-2.8±1.4‰). It may indicate that the contribution of coal combustion to sulfate in rainwater has decreased. Sulfur isotopes and chemical compositions of rainwater varied with the amount precipitation, when the amount of precipitation decreased, the contribution of coal combustion to rainwater sulfate increased, the sulfate concentration increased and the δ34S-SO42- value increased. The amount of atmospheric sulfate deposition in the karstic agricultural area, which controlled by coal burning and biogenic sulfur emissions, changed seasonally and fell in the S deposition range of from cities and forests. This study showed that upgrading of industrial structure and reduction of industrial coal burning can improve the air quality in Southwest China.
Keywords: karstic area; agricultural area; precipitation; water chemistry; sulfur isotopes
EARTH AND ENVIRONMENT Vol.47, No.6, Tot No.332, 2019, Page 811-819
