Geochemical Tracer Of River Water Pollution In The Fen River Basin

Rivers are one of the most important sources of fresh water resources that can be used directly by humans.Since the 20th century,the pollution of rivers has been increasing due to the influence of human activities.Investigation and treatment of water pollution have become the focus of environmental research in the global,and the quantitative study of the sources of water pollution has become one of the difficulties.The Fen River is the largest river in Shanxi Province.In recent years,the water pollution of the Fen River Basin（FRB）has become serious,and the deterioration of its water quality has become a bottleneck for industrial,agricultural and ecological development.Thus far,the water chemistry characteristics,the spatial-temporal variation of water pollution and control factors,and the contribution of human activities to the pollutants in the FRB are unclear.Based on the above consideration,river water was collected systematically in the dry season and the wet season in the FRB.Major ions,trace elements,boron isotopes,nitrogen isotopes and oxygen isotopes were analyzed to decipher the water hydrochemistry,the water quality and the sources of pollutants.This can provide a reliable scientific basis for water resources protection and pollution control in the FRB.The conclusions are as follows:（1）The river water in the FRB was weakly alkaline,and the average value of pH in the dry season and the wet season was 8.1 and 8.4,respectively.The average TDS of rivers in the FRB（the dry season:609 mg/L,the wet season:567 mg/L）was less than the average value of rivers in the Loess Plateau（897 mg/L）.The TDS in the river water was low values in the upstream（the dry season:370 mg/L,the wet season:333 mg/L）,high values in the midstream（the dry season:790 mg/L,the wet season:775 mg/L）,and medium values in the downstream（the dry season:762 mg/L,the wet season:690 mg/L）.The river water hadrochemical types of the upper,middle,and lower river water were Ca²⁺-HCO₃^-,Na⁺-Cl^-,Ca²⁺-Mg²⁺-Cl^-,respectively,and all affected by rock weathering.The seasonal variations of the main and trace elements in river water were also more obvious in the FRB,with high values of B,Ba,Fe,Li,Se,K in the dry season,high Ni,U,Cl,SO₄,HCO₃,Ca in the wet season.The values of Mg is greater than in the wet season.In the dry season,the spatial variation ofδ¹¹B(δ¹¹B,calculation method:δ¹¹B=[(¹¹B/¹⁰B)_sample/(¹¹B/¹⁰B)_standard-1]×1000,unit:‰)was obvious,shown the upstream（+5.1‰）<midstream（+8.6）‰)<downstream（+9.5‰）,and in the wet water period,the upstream（+6.1‰）<downstream（+7.2‰）<midstream（+9.0‰）.Theδ¹⁵N-NO₃^-value of river water showed increasing trend from upstream to downstream,while theδ¹⁸O-NO₃^-showed slightly decreasing trend.（2）The results of dissolved solute qualitative analysis in the FRB（principal component analysis-absolute principal component sore-multivariate linear regression,PCA-APCS-MLR）showed that evaporite dissolution and carbonate rock weathering were the main sources of dissolved solute,Ba,Mn,Ni,and U were from natural inputs,and As,Cu,Li,Rb,Se and V were from artificial inputs.The dissolved boron in river water mainly from silicate weathering（the dry season:38.8%,the wet season:49.2%）.Compared with other rivers showed that a relatively higher impact of anthropogenic inputs on dissolved boron in the FRB（the dry season:15.4%,the wet season:16.0%）.Source identification based on the Bayesian isotope mixing model（Mix SIAR）showed that riverine NO₃^-was mainly sourced from feces and sewage（the dry season:71.0%,the wet season:64.0%）.（3）The results of the water quality assessment showed that the exceeding rates of Mn,NO₃^-,and SO₄^2-in the dry season were 23%,51%,and 25%,respectively,the exceeding rates of Mn,NO₃^-,and SO₄^2-in the wet season were 20%,51%,and 20%,respectively,and these samples were in the midstream of the FRB;the river water of Huiji River,Wuma River,Changyuan River,Yangxing River,and Xiangyu River were not suitable for irrigation purposes.In the dry season,the water quality index（WQI）values of Huiji River and Shizi River were 119.6 and142.9,respectively.In the wet season,the WQI values of Sha River,Yuanpingchuan River,Jiaokou River,and Yangxing River were 796.0,274.4,158.1,and 104.3,respectively.The water quality of these river was poor.Health risk assessment showed that As,Ba,Mn,Ni,V,and Se were the potential pollutants damaging in the FBR.