Hydrochemical Characteristics Of Lhasa River Basin And Source Apportionment Of Heavy Metals In Water

Lhasa River is one of the largest and longest tributaries of the Yarlung Zangbo River basin.It is the main water source for life and production of residents in Lhasa River Basin.With the further economic and social development in the basin,pollution of the Lhasa River water body will inevitably occur.Some studies have found that As,Pb,Hg,Zn and other elements in the Lhasa River are relatively high.Heavy metal pollution has the characteristics of long incubation period,high toxicity and enrichment in the food chain,posing a threat to biological and human health.Therefore,the subject takes Lhasa River Basin as the research object.During the period of dry season,wet season and flat water period in 2016,we carried out systematic investigation of Lhasa River mainstream and its four major tributaries（Laqu,Xuerongzangbu,Mozhumaqu,Duilongqu）.Based on the data we obtain,I analyze the spatio-temporal changes of hydrochemistry in the river basin,assess the status of heavy metal pollution in water bodies,and analyze the sources of heavy metals.According to the analysis of chemical characteristics,the water bodies of Lhasa River mainstream and its tributaries showed weak alkaline（pH:7.79-9.2）,high self-purification capacity（DO>6.96 mg/L）,and partial oxidation（ROD:165-227 mV）.The overall salinity in the basin is high,and the TDS values of all sampling points are higher than the world average（97 mg/L）.Ca²⁺and HCO₃^-are the main ions with the largest spatial fluctuation.The seasonal variations of the total amount of anions and cations are as follows:flat water period>dry season>wet season.The hydrochemistry type of the Lhasa River main stream,Xuerongzangbu and Mozhumaqu is Ca²⁺-HCO₃^-,and the type of Laqu and Duilongqu is Na⁺+K⁺-HCO₃^-.Except for the F^-and Li,the concentration of trace elements in Lhasa River are generally low.There are differences in the relationship of different trace elements and seasonal changes.Combined with national water quality standards,the method of water quality index and Nemerow comprehensive pollution index were used to evaluate the heavy metal pollution in Lhasa River water body.The average concentrations of Hg,Cd,Pb,Cr,Cu,Zn,Mn and As of Lhasa River all reached Grade I standard,but the maximum value of As reached 170.45 ug/L.According to the results of water quality index and Nemerow index,the heavy metals in Lhasa River Basin belong to low pollution level,and Hg,As,Cu and Cr are the main heavy metal pollution elements.Based on the distribution of pollution sources in the basin,Pearson correlation analysis,principal component analysis and clustering analysis of sampling points,it can be inferred that the concentration of heavy metals in the main stream is controlled by natural factors and influenced by the life and production discharge of Lhasa City,Mozhumaqu is greatly affected by the mining wastewater,and Duilongqu is greatly affected by the impact of geothermal water.Mn,Cd and Cu are mainly from the endogenous release of rivers,As is mainly from geothermal wastewater,and Pb and Zn are mainly from the input of mining wastewater.