喜马拉雅山中段北坡地表水体主要离子特征及其控制因素——以叶如藏布流域为例

Major ions and their controlling factors of surface water in the northern slope region in the middle Himalayas: A case study of Yairuzangbo Basin

为调查喜马拉雅山中段北坡地表水环境特征,2015年9月在叶如藏布流域采集24个地表水体水样并对其水化学特征分析测定,研究结果表明:(1)叶如藏布流域水化学特征存在显著空间差异.随着海拔升高,地表水体p H值、TDS值呈微弱的减小趋势.24个水样中23个水样属于淡水,1个为微咸水.(2)叶如藏布流域内地表水阳离子主要为Ca^(2+),阴离子以SO_4^(2-)为主,其次为HCO_3^-,即地表水为Ca^(2+)-SO_4^(2-)型.(3)叶如藏布流域地表水中各离子之间具有不同程度的相关性.其中Cl^-、HCO_3^-、Na^+和K^+4种离子共源性好;阳离子的来源不同,Na^+和K^+主要来源于碳酸氢盐,Ca^(2+)主要来源于硫酸盐,而Mg^(2+)的来源比较广泛.(4)叶如藏布流域大部分离子主要来源于陆地,受陆源影响从小到大排列顺序为:Na^+<Mg^(2+)<SO_4^(2-)<Ca^(2+)<K^+<HCO_3^-.流域水文化学过程主要受岩石风化作用控制,特别是受到碳酸盐风化影响.以强木村为界,流域下游地区地表水化学特征受人类活动影响逐渐变大,特别是畜牧活动及人类施肥的影响.

The chemical characteristics of surface water can reflect the climate and environmental background of the region. In order to investigate the hydrochemical characteristics in the northern slope of the middle Himalayas,24 water samples of glacial lake,river,wetland and precipitation were collected in the Yairu Zangbo Basin in September 2015,and were then analyzed. The results show that the hydrochemical characteristics exhibited a significant spatial diversity in the Yairu Zangbo Basin. The p H and TDS values of water samples present a weak decrease trend as elevation rises. All the samples belonged to fresh water except one identified as brackish water. The predominant cation of surface water was Ca^（2＋）and the main anion was SO_4^（2-）,followed by HCO_3^-. This means that the water was characterized by Ca^（2＋）-SO_4^（2-）in the Yairu Zangbo Basin. There were different correlations among all theions. In particular,four ions including Cl^-,HCO_3^-,Na~＋and K~＋had a strong co-originality. However,cations originated from different sources. For instance,Na~＋and K~＋mainly came from bicarbonate,Ca^（2＋）was mainly from sulfate,and the source of Mg^（2＋）was wide. Meanwhile,it was revealed that the main ions are mainly originated from terrestrialdust using the sea-salt ions tracer method in the Yairu Zangbo Basin. According to the influence of terrestrial dust,the order of ions was： Na~＋Mg^（2＋）SO_4^（2-）Ca^（2＋）K~＋HCO_3^-. This implied that the hydrochemical process was mainly controlled by rock weathering in this basin,especially the natural weathering of carbonate rock. The human activities such as herding and fertilization had a growing impact on hydrochemical characteristics of river and wetland at the downstream area below the Qiangmu Village.