基于“水文频率-水质”拟合曲线的河流水质变异与等级特征值分析方法

River water quality variation and grade characteristic values analysis method based on“hydrological frequency-water quality”fitting curves

时空特征分析对全面掌握水质变异规律具有重要意义,但现有的水质时空特征分析方法仍存在水质变异次序不分、水质变幅极值不清、水质评价特征值不明等不足。为更加清晰地探析水质时空特征信息,以秦淮河为研究对象,参考工程水文学经验频率法,建立“水文频率-水质”拟合曲线用于探索流域内高/低活动区不同时间段和丰/枯水期不同河段水质变异特征,并与传统的箱线图法进行对比。结果表明:与箱线图相比,“水文频率-水质”拟合曲线可量化关键水质评判点与特征值信息,使水质时空变异过程更为清晰。在时间上“水文频率-水质”拟合曲线的最佳形式为线性曲线,水质浓度一般不会发生突变;在空间上“水文频率-水质”拟合曲线的最佳形式为指数曲线,水质浓度有较大可能发生突增。各时间段高活动区氮磷浓度大于低活动区,各水体断面丰水期氮磷浓度低于枯水期。该方法分析过程简单方便,结果直观有序,能将水质信息以统计规律自动反映出来,在水质采样点、采样时间和采样频率典型时可作为优选方法用于河流水质时空特征研究。

The analysis of temporal and spatial characteristics is of great significance for comprehensively understanding water quality variation.However,the existing temporal and spatial water quality analysis methods still have some shortcomings,such as indistinguishable order of water quality variation,the unclear extreme value of water quality variation,and unclear water quality evaluation characteristic values.To analyze the temporal and spatial characteristics information of water quality more clearly,this study took Qinhuai River as a research object and referred to the empirical frequency method of engineering hydrology.A“hydrological frequency-water quality”fitting curve was established,which was used to explore the difference between high/low activity areas in different periods and wet/dry seasons in different reaches.The“hydrological frequency-water quality”fitting curve method was compared with the traditional boxplot method.The results showed that compared with the boxplot,the“hydrological frequency-water quality”fitting curve could quantify key water quality evaluation points and characteristic value information,making the temporal and spatial variation process of water quality clearer.The best form of the“hydrological frequency-water quality”fitting curve in time was the line number curve,and the water quality concentration generally did not change abruptly.The best form of the“hydrological frequency-water quality”fitting curve in space was an exponential curve,and the water quality concentration had sudden increases were more likely.The concentration of nitrogen and phosphorus in the high activity area was higher than that in the low activity area during each period,and the concentration of nitrogen and phosphorus in the wet season of each river section was lower than that in the dry season.The analysis process of this method was simple and convenient,the results were intuitive and orderly,and the water quality information could be automatically reflected by statistical analysis.It could be used as an optimal method to study the temporal and spatial characteristics of river water quality when the sampling points,sampling time and sampling frequency are typical.