西藏年楚河流域水化学特征分析

Hydrochemical Characteristics of Nyangchu River Basin in Tibet

年楚河流域是西藏发达的农业区,有"西藏粮仓"之称,对区域经济发展起着决定性的作用。然而对该流域水体水化学的系统研究鲜见报道。为揭示年楚河流域水化学特征及其控制因素,本研究于2018年11月(平水期)对年楚河主干流及其主要支流的水体理化参数、主要离子和微量元素进行分析研究。结果表明,年楚河流域水体总体呈弱碱性,总溶解性固体、电导率和矿化度均值分别为275.64 mg/L、389.06μS/cm和172.71 mg/L,且空间上均表现为自上游至下游递增的趋势。主干流及其主要支流阳离子以Ca^(2+)为主,占阳离子总量的71.45%,阴离子则以HCO_(3)^(-)为主,占阴离子总量的63.21%。河水主要离子浓度在空间上表现出一定的差异性,整体上主干流自上游至下游有逐渐递增趋势,河口段则相对平稳。年楚河三个主要源头湖泊区域中,错嘎布和冲巴雍错及下游出水口附近水体水化学类型主要为HCO_(3)-Ca型,桑旺湖及主干流上中游和雅鲁藏布江汇入口附近河段水化学类型为HCO_(3)·SO_(4)^(-)Ca·Mg型,而下游区域,包括支流冲巴涌曲下游和龙马河的水化学类型主要为HCO_(3)·SO_(4)^(-)Ca型。流域内碳酸盐岩和硅酸盐岩的风化作用是控制整个流域水化学特征的主要因素,且自源头区到下游河段其主导控制风化作用由碳酸盐岩逐渐过渡为硅酸盐岩。流域内以农业为主的人类活动对河流水环境造成的潜在影响不可忽视。

The Nyangchu River basin is called"The granary of Tibet"and plays a decisive role in regional economic development.Report on systematic studies of water chemistry in the area was few.In order to reveal the water chemical characteristics and its controlling factors of the river basin,water samples were collected in November 2018(Level period)from the river main stream and its major tributaries for a hydrochemical characteristics evaluation.Collected water samples were mainly measured for its physiochemical parameters,including major ions and trace elements.The results showed that water from the Nyangchu River basin was slightly alkaline,with p H range from 8.10 to 9.41.A similar spatial trend,i.e.increased from upstream to the downstream,appeared for total dissolved solids(TDS),electrical conductivity(EC)and salinity(Sal.).Average value of TDS,EC and Sal.were 275.64 mg/L,389.06μS/cm and 172.71 mg/L,respectively.Among which,Ca^(2+)was dominated cation,accounting for 71.45%of the total cations,while the anions was dominated by HCO_(3)^(-),accounting for 63.21%of the total anions.The concentration of major ions in the river showed a certain difference in terms of spatial variation.Over all,these ions increased gradually from the upper to the middle catchments and,stabilized on the river confluence,where it runs to the Yarlung Tsangpo.Among the three major source areas(i.e.Tsokarpu lake,Chumbyumco lake and Sawang lake),water hydrochemical of Tsokarpu lake,Chumbyumco lake and its downstream outlet were mainly HCO_(3)-Ca type,however,Sawang lake,upper to middle reaches of the Nyangchu river main stream as well as the estuary of the Yarlung Tsangpo River were HCO_(3)·SO_(4)^(-)Ca·Mg type.Water hydrochemical types for the downstream areas,including its tributaries(i.e.Chong Ba Yong Qu and Longma River),were mainly HCO_(3)·SO_(4)^(-)Ca.Weathering of carbonate and silicate rocks in the river basin was the major controlling factor of the water chemical characteristics.Nevertheless,the controlling intensity was gradual transited from carbonate to silicate weathering along the river course.In addition,the potential impact of agricultural runoff in the river basin cannot be ignored.