The hydrochemistry properties of precipitation in karst tourism city (Guilin), Southwest China

A comprehensive study on the chemical compositions of rainwater was carried out from January 2008 to November 2011 in Guilin, China. The 396 samples were analyzed for pH and electrical conductivity, and 44 among of 396 samples were analyzed for major ions. The result shows that pH value ranges from 3.44 to 7.16, and the occurrences of acid rain may increase with natural factors and human activities. The order of the main ion concentration in precipitation is SO4 2− > Ca2+ > NH4 + > NO3 − > Cl− > Na+ > F− > Mg2+ > K+ (weighted average). The correlation of the main cations, neutralization factors (NF), enrichment factor, and ionic ratio shows that acid rain can be mitigated slightly by the neutralization effect of a large amount of alkali ions. The SO4 2−, NO3 −, NH4 +, and a fraction of Ca2+ may originate from emissions of human activities, and the K+, Mg2+, and a majority of Ca2+ may originate from weathering of soil and rock. Mg2+ may transport long distance from large cities in the surrounding area. Among them, hyper-accumulation of NO3 − is produced by lots of vehicle and festival emissions. The hydrochloride may increase rainfall acidity, which refers to the temporary acidity. In addition to the input of pH value and acid ions, the input of alkali ions should be considered in the future evaluation of acid deposition in cites.