西藏扎日南木措流域水环境特征及其影响因素

Characteristics of Water Environment and Its Influencing Factors in Zhari Namco Basin,Xizang

扎日南木措位于藏西北高寒草原带,为西藏第三大湖,生态环境脆弱,长期以来其流域水环境的研究资料缺乏,为探究其流域地表水环境特征及影响因素,于2021年8月~2022年6月丰、枯、平水期对流域湖泊和入湖河流水环境进行调查,结合数理统计以及水化学分析、相关分析和主成分分析等方法,对流域水化学特征进行了评价,分析了水质时空差异特征,并对水质影响因素进行了探讨.结果表明:①扎日南木措流域水体呈碱性,湖水离子组成以Na^(+)、SO_(4)^(2-)和Cl^(-)为主,河流以Ca^(2+)、HCO_(3)~-和SO_(4)^(2-)为主.②硫酸盐、砷、氯化物和总磷为主要超标污染物,流域水质存在明显时空差异.时间上,硫酸盐、砷和总磷超标均表现为:丰水期>枯水期>平水期,氯化物的水期差异不明显;空间上,河流水质优于湖泊,湖泊中砷、总磷、TDS、硫酸盐、氯化物、K^(+)和Na^(+)的浓度较河流高1~2个数量级,水质超标现象基本集中于湖区,而湖内水质空间差异小.③流域水化学过程主要受蒸发-浓缩和岩石风化下的自然过程控制,各类元素经地表径流进入湖泊后,在蒸发浓缩作用下不断富集最后产生超标.④水质时间差异主要是丰水期更多的元素淋失和更强烈的蒸发作用导致;而空间差异则主要是流动水体和封闭水体的水动力条件差异导致.

Zhari Namco is situated in the alpine grassland belt of northwestern Xizang with a fragile ecological environment.As the third-largest lake in Xizang,there has been a longterm lack of research data concerning its basin water environment.In an effort to elucidate the surface water environment characteristics of the basin and the factors influencing them,an extensive investigation was conducted from August 2021 to June 2022,encompassing periods of high flow,low flow,and base flow.Further,the study also involved comprehensive assessments of the water chemistry characteristics and spatial-temporal variation in lake sampling sites of the basin that were not significant by using mathematical statistics,hydrochemical analysis,correlation analysis,and principal component analysis.The findings revealed the following:①The water in the Zhari Namco Basin exhibited an alkaline nature,with dominant ionic compositions in the lake comprising Na^(+),SO_(4)^(2-),and Cl-,whereas the rivers were primarily characterized by Ca^(2+),HCO_(3)^(-),and SO_(4)^(2-).②The main pollutants exceeding established standards included sulfates,arsenic,chlorides,and total phosphorus.The study identified significant spatiotemporal variations in water quality.Temporally,the exceedance of sulfates,arsenic,and total phosphorus was most pronounced during high-flow periods,followed by that during low-flow and base flow periods,with chloride levels showing less temporal variation.Spatially,river water quality surpassed that of the lakes,with arsenic,total phosphorus,TDS,sulfate,chloride,K^(+),and Na^(+)concentrations in lakes 1 to 2 orders of magnitude higher than those in rivers.Water qualities exceeding the established standard were primarily found in the lake,with less spatial variations within the lake itself.③Hydrochemical processes within the basin were found to be primarily influenced by natural phenomena,including evaporation-concentration and rock weathering.Various elements entered the lakes via surface runoff,where they continuously accumulated under the influence of evaporation-concentration processes,ultimately leading to exceedances.④Temporal variations in water quality were primarily attributed to increased elemental loss and intensified evaporation during high-flow periods.The spatial discrepancies in water quality were predominantly a consequence of the differing hydrodynamic conditions between flowing water bodies and enclosed water bodies.