Chemical Characteristics of Precipitation at the Headwaters of the rümqi River in the Tianshan Mountains
HOU Shu gui (Laboratory of Ice Core and Cold Regions Environment, CAREERI, CAS, Lanzhou Gansu 730000, China)
During the period June, 1995 to June, 1996, all precipitation events were sampled at the headwaters of the rümqi River in the Tianshan Mountains, China. The samples were analyzed at Laboratory of Ice Core and Cold Regions Environment, CAREERI, CAS, for major ions (K + , Na + , Ca 2+ , Mg 2+ , Cl - , NO - 3 and SO 2- 4), pH and conductivity. It is found that Ca 2+ dominates the cations, while SO 2- 4 dominates the anions among the measured major ions. The concentration amplitudes are 0~12 63 μ g·g -1 for Ca 2+ , 0~2 06 μ g·g -1 for Mg 2+ , 0 03~5 56 μ g·g -1 for Na + , 0~5 57 μ g·g -1 for K + , 0 19~40 46 μ g·g -1 for SO 2- 4, 0~11 58 μ g·g -1 for NO - 3 and 0~24 43 μ g·g -1 for Cl - , respectively. The results of EOF (Empirical Orthogonal Function) analysis and correlation analysis indicate that the chemicals in precipitation originate from four sources, namely, the regional Asia dust, local coarse dust, anthropogenetic component, and sea (and/or saline lakes) salt. EOF1 explains 60 5% of the total variance in the multi variables, and all the ions, as well as pH and conductivity, are positively correlated with in EOF1 associations, which might reflect the influence of the regional Asia dust on precipitation chemistry. Ca 2+ and Mg 2+ dominate EOF2 associations (explaining 50 3% and 37 5% of their corresponding total variances), which are also negatively correlated within all the other ions, reflecting the influence of the local coarse dust. NO - 3 and pH dominate EOF3 associations, which are negatively correlated, thus it is suggested that EOF3 might represent the acidic component deduced from the local anthropogenetic activities. K + , Na + and Cl - dominate EOF4 associations, which might reflect the material originated from sea (and/or saline lakes) salt. Although the chemical characteristics of precipitation is basically controlled by contribution of regional Asia dust, over half of Ca 2+ comes from the local dust. Moreover, NO - 3, rather than SO 2- 4, it represents the local contamination and determines the acidity of precipitation, because EOF3 can only explain 2 1% of the total SO 2- 4 variances. Material originated from sea salt or nearby saline lakes only plays a minor role in the precipitation chemistry.