中文摘要：

资料匮乏区地表水化学特征调查是区域环境研究的基础，也是识别气候变化、地质构造等环境因素与径流过程相互作用的有效途径。基于2013年和2014年实测的离子化学数据，利用Gibbs相关分析及离子关系对比等经典地质化学分析方法，对蒙古中北部主要湖泊和河流离子化学特征及其主要控制因素进行分析。结果表明：该地区地表水体呈弱碱至碱性，河水中TDS平均值约为114．0mg／L，并具有明显的空间差异。Ca^2＋和HCO3^-普遍为该区地表水体中的优势离子；地表水体中离子主要来源于岩石风化过程，且以碳酸盐和硫酸盐矿物的风化作用最为强烈。该区目前地表水体水质呈良好状态，但硝酸盐呈一定的积累态势，因此人类活动对该区域水质的影响需要引起高度重视。

英文摘要：

Investigation of geochemistry of surface water is a fundamental study of the regional environment in ungauged areas. Also the study is helpful to determine the relationship between hydrological processes and environmental factors including the climate change and geologic structure. Sampling of the lake and river waters in the northern-central parts of Mongolia was carried out in 2013 and 2014. Then, using the measured chemical data of water solutes, the ion compositions and its controlling factors were analyzed preliminarily. The traditional methods in geochemistry, such as Gibbs correlation analysis and Stoichiometry, were applied in this study. Results indicate that the waters in the study area are from slightly alkaline to alkaline. The average value of total dissolved solids in river waters is about 114.0 mg/L, which presents a significantly different spatial variation of ion compositions in river waters. However, generally Ca2 ＋ and HCOf are the dominant ions in the surface waters in the study area. The most important source of the solutes in the surface waters is rock weathering process. In particular, the contribution of carbonate and sulfate minerals weathering are the largest. Although the current water quality is in a good situation in the northern-central parts of Mongolia, an accumulating trend of the nitrate in waters has been detected. Therefore, great attention should be paid to the influence from the anthropogenic input.