With the rapid economic development, the fossil fuels consumption increases speedily, and the total amount of the pollutants released by human activities into the atmosphere such as sulfur dioxide (SO2) and nitrogen oxides (NOx) keeps growing. As a result, the pH of rain decreases and causes acid rain.
The karst region of southwest China is one of the earliest areas experiencing acid rain and remains an important area for acid rain research. Previously, most studies of the rainwater focus on karstic urbanized or remote areas (e.g. Prof. HAN Guilin at the Institute of Geochemistry, Chinese Academy of Sciences (IGCAS) has monitored the rainwater of Guiyang and Maolan Forest for years). However, very few studies have been done for the karstic agricultural area which is notified as eco-fragilezone and strongly connected to human survival.
When acid rain enters the soil, it not only inhibits the decomposition of organic material and the nitrogen fixation, but also leaches away the ions of calcium, magnesium, potassium and other essential nutrients in the soil. Those actions result in poor soils and withered crops. Hence, it is crucial to study the rainwater of the agricultural area.
Prof. HAN Guilin’s group at IGCAS focused on Puding, a typical agricultural area located in the middle karst region of southwest China, and collected the rainwater samples in Puding during the rainy period (March to October) in 2008.
Although the rainwater samples collected in Puding contained relatively high concentrations of acid components SO42-and NO3- , the researchers found that the samples exhibited relatively low acidity. Their acid neutralization analysis revealed that most of the acidity in the sampled rainwater was neutralized by large amount of alkaline ions (Ca2+, Mg2+, NH4+) in the karst soil dusts.
Moreover, the chemical analysis of rainwater and the back-trajectory analysis brought to the conclusion that the rainwater ion composition of Puding was significantly affected by urbanization, which meant that urbanization changed the atmosphere of the urban area as well as that of the agricultural area.
The results were published in Atmospheric Research and titled Chemical composition of rainwater in a karstic agricultural area, Southwest China: The impact of urbanization.
(Provided by WU Qixin, translated by XIAO Yi)
