Abstract: Tarim River Basin,located in southern Xinjiang,China,is a typical and the largest inland river in China, which plays an important role in regional ecological environment protection and social development. Research on the spatial characteristics of river hydrochemistry and its controlling factors of Tarim River Basin is of great significance for water environment management. The hydrochemistry characteristic is affected by bedrock property,local climate and human activities. In current research,field surveys were conducted in August and September 2011 and 72 surface water samples were collected from the main stream and 4 major tributaries including Aksu River,Hotan River,Kaidu River and Weigan River. Total Dissolved Solid(TDS),pH values,concentration of Na⁺,K⁺,Ca²⁺,Mg²⁺,HCO₃^-,SO₄^2- and Cl^- of all water samples and stable hydrogen and oxygen isotopes of part of the samples were measured in laboratory for analyzing the spatial characteristics of hydrochemistry and its controlling factors. Through Hierarchical Cluster Analysis(HCA)method,we found that the surface water samples of Tarim River Basin could be clearly categorized into three groups including four water types. The first group is Mg-Ca-HCO₃ type that mainly represents the water type at the lower reaches of Tarim River. The second group includes two different water types,Ca-Mg-SO₄-HCO₃ type and Na-Mg-SO₄-HCO₃ type,which represents the water type in Aksu River and upper reach of Tarim River,and Hotan River,respectively. The third group is Mg-Ca-HCO₃ type which represents water type in Kaidu River. Gibbs graph was applied as a direct method to evaluate controlling factors of hydrochemistry in this study. Hydrochemical component of most water samples were distributed in the middle area of Gibbs graph,indicating that the hydrochemical component in this basin was mainly controlled by rock weathering. Ions stoichiometry analyzing was applied to determine ions weathering source. Results revealed that Na⁺ are derived from silicate weathering in Aksu River,while Ca²⁺ and Mg²⁺ are derived from dolomite,calcite and gypsum weathering. In Hotan River,Na⁺ is derived from silicate weathering and Ca²⁺ from calcite,Ions in Kaidu River is mainly derived from dolomite weathering. Halite,gypsum and epsomite were the major weathering sources in the mainstream of Tarim River,especially in the lower reach of Tarim River. Finally,the D-excess value were calculated by using stable hydrogen and oxygen isotopes values of samples from lower reaches of Tarim River to recognize climate influence on river water chemistry,and result of 17.2%-23.2% of increasing TDS originated from evaporation was obtained. It indicated that hydrochemistry of Tarim watershed had distinct spatial variation and regional rock mineralogy had different hydrochemical type. Hydrochemical composition of upper Tarim River was largely effected by Aksu River and showed Ca-Mg-SO₄-HCO₃ water type. But hydrochemistry of the middle and lower reaches of Tarim River was mainly affected by evaporation. Therefore river water salinity increased and chemical composition changed from upper to lower reaches.

Key words: Tarim River, hydrochemistry, major ions, rock weathering