Study On Temporal Change Characteristics Of Urban River Water Quality

To reveal the spatiotemporal change characteristics of water quality for a designated reach of Ancient Canal in Yangzhou city,a reach of Yangnong Chemical Plant to Sanwan Scenic Area was chosen as the study location.The observation of water quality parameters such as water temperature(WT),pH,electrical conductivity(EC)and dissolved oxygen(DO),and the concentration of pollutant ions(NH4+,etc)had been carried out in the main stream and tributary inflow sections of the study area,and the coefficient of variation method,single factor water quality index method and multiple linear regression method were adopted to analyse the variation characteristics of the water quality parameters,evaluae the water quality category and interactions between water quality parameters.A one-dimensional flow-following dispersion of pollutant was developed for the numerical simulation of changed process of NH4+ concentration in the reach of the Sanwan Scenic Area.The main research results are as follow(1)WT at each section showed seasonal changes.DO on the sections of main stream of the chemical plant reach decreases with the increase of WT,and increases with the increase of pH;the DO of the main stream in the study reach decrease from upstream to downstream in most of periods,while the EC increase from upstream to downstream;the DO,EC and pH of the sections of the tributaries showed a strong randomness.(2)The variation coefficient of WT in the first and fourth quarters is greater than that in the second and third quarters during the same year;the variation coefficient of DO in most quarters is greater than other parameters in the same period;the variation coefficient of pH in most quarters is less than 0.1,with little fluctuation;the weight of each water quality parameters in the sections of Andun River(one of the tributaries of the chemical plant reach)is DO>EC>WT>pH in descending order,while the other sections are DO>WT>EC>pH;the contribution of DO to water quality change and relative importance of DO is the highest.(3)During the study period,when WT is lower than 20? and pH is higher than 7.5(in the first and fourth quarters),the water quality category of the reach of chemical plant is mostly?,? or ?,while in the second and third quarters,the water quality category is mostly inferior to ?;the water quality category is mostly IV,V or inferior V in the sections of tributaries,and the change process of water quality identification index have strong randomness.(4)DO is negatively correlated with WT and positively correlated with pH;except for the tributary sections of Sanwan reach,the linear relationship between DO and WT,pH is significant;the WT and pH of the main stream sections of Sanwan reach have significant impact on DO,the WT of upstream section of the main stream and the sections of tributaries of chemical plant reach have significant impact on DO,while the impact of pH is not significant,and the WT and pH in the sections of tributaries of Sanwan reach have no significant impact on DO.(5)When the temperature coefficient ? is 1.02 or 1.04,the simulation accuracy of model increase first and then decrease with the increase of coefficient a,and the the simulation accuracy when ? is 1.04 is higher than that when ? is 1.02;when 8 is 1.06,the simulation accuracy decrease first and then increase with the increase of coefficient a;when a is 3.5 and? is 1.04,the overall simulation accuracy of model is the highest.(6)The Nash-Sutcliffe efficiency coefficient(NSE)of the upstream section of Sanwan reach is 0.960,and the NSE of the downstream section of Sanwan reach is 0.582,the simulation accuracy of upstream section is high,and that of downstream section is generally reliable;the average error of the simulation results of upstream section is 0.288 mg/L,and that of downstream section is 0.687 mg/L;the simulation results indicate that the concentration of NH4+ in the upper reaches gradually decrease in a single day,and that in the lower reaches increase gradually,finally,the concentration of NH4+ in each section tends to the same level.