Abstract: In order to determine the characteristics and sources of the chemical composition of precipitation in Qilian Mountains,Gansu Province,China,a total of 44 precipitation samples were collected from individual precipitation events at the meteorological station of Minle County from May 2013 to July 2014,which located in low coteau of Qilian Mountains. All precipitation samples were analyzed for major cations(Na⁺,K⁺,NH₄⁺, Mg²⁺ and Ca²⁺),anions(Cl^-,NO₃^- and SO₄^2-),pH and electrical conductivity(Ec)using water chemistry measurement with Dionex-600 and Dionex-300. Results show that the average precipitation pH value was 7.44,while the precipitation Ec values ranged from 4.0 μs·cm^-1 to 940.0 μs·cm^-1 with an average value of 167.93 μs·cm^-1. During the entire sampling period,the concentrations of cations and anions decreased in the order of Ca²⁺> SO₄^2-> NH₄⁺> Cl^-> Na⁺> NO₃^-> Mg²⁺> K⁺ . The total cation concentrations were greatly higher than the total anion concentrations. Ca²⁺ is the dominant cation in precipitation with an average value of 624.82 μeq·L^-1 (0.95-2 061.40 μeq·L^-1),accounting for 47% of the total cations in precipitation. SO₄^2- is the predominant anion, accounting for 44% of the total anions. Precipitation in low coteau of Qilian Mountains was of Ca²⁺ and SO₄^2- type. The concentrations of these main ions were relatively high compared to those reported in other regions of Qilian Mountain. Seasonal variations of ions indicate that cation and anion concentrations in summer season were relatively lower. However,the precipitation events show higher cation and anion concentrations during winter and spring. Frequent sand storm in winter and spring resulted in a high concentration of continental atmospheric aerosols,which finally promoted the ion concentrations in these two seasons. Correlation and Main factor analysis indicate that regional crustal aerosols and species are the major sources for these ions,agricultural activity and aerosols from human pollution are the secondary sources,and the contribution of sea salt was the least due to the long distance transport. By analyzing the chemical composition of precipitation in different seasons,it is easy to know the variations and sources of precipitation ions during the sampling period. Additionally,it can contribute to analyzing the degree of human survival environment deterioration in low coteau of Qilian Mountains in the future.

Key words: precipitation, chemical ion, environment, Qilian Mountains