Study On The Response Of Trace Elements In Urban Rivers To Human Activities And Wastewater Tracer Based On Continuous Samplin

The hydrogeochemical processes of trace elements are of great significance to the assessment and utilization of river water resources in karst areas.Urban areas are often densely populated,industrially concentrated and medically developed,especially with the development of high-tech and new industries in cities,leading to the entry of trace elements into water bodies and changing the geochemical characteristics of trace elements in natural rivers around cities.Therefore,this paper takes a typical urban river（Nanming River）and the largest wastewater treatment plant（Xinzhuang Wastewater Treatment Plant）along it in Guiyang City as the research object,and conducts continuous collection of 162 transient water samples from the inlet and outlet of the wastewater treatment plant and the river after the confluence of wastewater discharge,determines and analyzes the concentration,temporal and spatial changes of major ions and trace elements and identifies their controlling factors to explore the influence of the wastewater treatment plant discharge on the downstream of the discharge The study also investigated the dynamic response of trace elements to the effluent of the wastewater treatment plant.The main findings of this study are as follows:（1）The main ions in the river water of Nanming River are mainly Ca²⁺,Mg²⁺and HCO₃^-,and the water chemistry type is HCO₃-SO₄-Ca-Mg type.The variation of TDS in Nanming River ranged from 447～727 mg/L,with a mean value of 645±98.9mg/L,which was much higher than the mean value of the world rivers.Spatially,Na⁺,Cl^-and SO₄^2-in Nanming River showed a characteristic of dramatically increasing in the midstream urban river section and maintaining high levels in the river water downstream of the wastewater treatment plant discharge.The Piper diagram and ion ratios show that Ca²⁺,Mg²⁺and HCO₃^-are mainly influenced by carbonate rock weathering;SO₄^2-shows the characteristics of sulfuric acid involved in carbonate rock weathering;Cl^-,NO₃^-and Na⁺are mainly from anthropogenic activities.（2）The average concentration order of trace elements is Fe>Ti>Zn>Mn>Li>Ni>Cu>Cr>Co.Most of the trace elements in Nanming River are mainly in the true dissolved state,while Mn is mainly in the larger colloidal state（10 kDa-0.22μm）（95.61%）.Spatially,the trace element content of Nanming River varied similarly along the river,both showing a sharp increase in the midstream urban section and maintaining high levels in the river water downstream of the wastewater treatment plant discharge.The results of water quality assessment and health risk assessment indicate that the Nanming River has good water quality.The co-tracer method using urban source trace elements combined with traditional tracers(Cl^-/SO₄^2-,etc.)found that urban activities and wastewater treatment plant effluent were the main influencing factors of trace element content in the Nanming River.（3）Based on continuous sampling（one week）of inlet and outlet water of wastewater treatment plants and upstream and downstream river water,the response patterns of water chemistry and trace elements in urban rivers to the discharge of wastewater treatment plants were analyzed.The results showed that the Na⁺,K⁺and Cl^-contents showed an overall decreasing trend with time,while the remaining ions changed more slowly.The time-dependent characteristics of Cl^-and NO₃^-at the downstream point of the outfall（XZ-2）are somewhat similar to those of the wastewater treatment plant effluent.The trace element contents on working days were significantly different from those on weekends,and the trace element contents on the two weekend days were significantly lower than those on working days.（3）Three methods（one-way ANOVA test,principal component analysis,and mixed equation）were used to identify inorganic tracers with good potential for the discharge of wastewater treatment plants along the Nanming River.ANOVA test results showed that the Na⁺,K⁺,Ca²⁺,Cl^-,NO₃^-,SO₄^2-,Li,Mn,Co,Ni,and Zn in the effluent from the sewage treatment plant were significantly higher than those in the river water.The principal component analysis also proves that Na⁺,K⁺,Cl^-,NO₃^-,Li,Mn,Co,Ni,and Zn are closely related to the emissions from sewage treatment plants.The results of the mixed equation indicate that the contribution values of NO₃^-（29.33%）,Mn（35.26%）,and Ni（32.15%）are within±5%of the conservative ions（Cl-has a contribution value of 32.48%）.Except for the conservative ions,these three indicators are considered to be the most potential tracers for indicating wastewater discharge from Xinzhuang Wastewater Treatment Plant.