Study On The Trend Balance Points Of Water Quality Evolution Of Yangtze River In Response To Water Function Zoning Management

In order to realize the rational development,effective protection,comprehensive management and scientific management of water resources,Chinese government adopts water function zoning management to protect water resources.During the implementation of the water function zoning management for more than ten years in China,good performances have been achieved,but there are also some deficiencies.The evaluation of the effect of water function zoning management on China's water resources protection and what role it currently plays in China's rivers and lakes protection is a subject of great research value and far-reaching significance.It can provide reference value and scientific basis for China to further implement water function zoning management and better protect water resources,water environment,and water ecological.Based on the understanding of water function zoning management,this paper puts forward the concept of trend balance points.In order to verify those trend balance points and evaluate the effectiveness of water function zoning management in China,this paper takes the main stream of the Yangtze River as the research area,demonstrates from two aspects.First,based on the analysis of big data,the time evolution trend of the Yangtze River water quality was studied.Second,based on remote sensing of water quality,the spatial evolution of Yangtze River water quality was conducted.According to the above,this paper mainly completes the following aspects:(1)Based on the understanding of water function zoning management,put forward the concept of trend balance points.That is under the existing water function regional management system,the water quality will tend to be an equilibrium state that gradually approaches the control target of the water function zone and ultimately make fluctuates somewhere below it.This study demonstrates the concept from two perspectives:time evolution and spatial evolution.(2)Collect and collate data on the water quality of the mainstream of the Yangtze River.This paper collects data from several water quality indicators of 92 monitored sections of the mainstream of the Yangtze River through data mining from five sources.Collates,statistics,and analyzes the data.Evaluation of mainstream water quality of the Yangtze River.And the result shows that the TP pollution is most serious in the main stream of the Yangtze River.Followed by Pb,NH3-N,Hg,CODMn,OIL,DO,and BOD5.The integrated water quality of the mainstream of the Yangtze River continued to improve and tends to be converted to ?-?.(3)Based on the time series,the time-evolving trend analysis of 8 pollution indicators in each section of the main stream of the Yangtze River was analyzed.The DF test method was used to test the stability of the water quality time series.And it was found that more than 90%of the sections DO and TP have stabilized,60%of the sections of CODMn,NH3-N,BODs,Pb,and OIL have stabilized,indicating that the water quality of the main stream of the Yangtze River has a steady trend in time evolution,that is,the water quality of the mainstream of the Yangtze River exists trend balance points.The ARIMA model was used to predict the trend balance points.The result shows that the trend points are in good agreement with the basic changes of the control target of the water function zone.But the peaks or troughs of the inflection points of some river sections are earlier or later than the control target of the water function zone.In summary,it can be considered that the water quality of the mainstream of the Yangtze River tends to the control target of the water function zone from the perspective of time evolution.(4)Water quality remote sensing spatial sensitivity analysis.Taking distance X as the indicator index,and the correlation coefficient R,the coefficient of determination R2,and the relative error RE as discriminant indexs.Choosing the upper,lower and Three Gorges reservoir areas as three typical study areas.Water quality remote sensing spatial sensitivity was studied to provide reference and basis for water quality remote sensing of mainstream of the Yangtze River.The results show that the indicator index X has an optimal effect between 75 and 400 m.Considering comprehensive consideration,this study takes X=200 m.(5)Using the result of water quality remote sensing spatial sensitivity analysis,based on the Landsat satellite imagery and ground-based observational water quality data,and analyzing the correlation between water quality indicators and remote sensing bands and band combinations,a multivariate linear regression model was used to construct a water quality remote sensing inversion model for mainstream water quality in the Yangtze River.The reliability and fault-tolerance analysis was performed on the model and the model was used to invert the concentration of water quality indicators of the mainstream of the Yangtze River in 2016,2015,2014 and 2013.The single-factor assessment method was used to further determine the spatial distribution of the integrated water quality categories of the mainstream of the Yangtze River,and compare it with the target districts of water quality control in functional areas.The results show that the water quality in 2015,2016 and 2014 was basically Grade ???water,but in 2014,the Grade ? water was significantly more than in 2016 and 2015.In 2013,the water quality was mainly Type ? water,but there are many types of water worse than Grade ?.Considering the control target of the water function zone are basically Grade ???,so from the perspective of the spatial evolution of water quality,it can be thought that the water quality of the main stream of the Yangtze River tends to the control target of the water function zone.From the point of view of spatial evolution of water quality,the water quality of the main stream of the mainstream of the Yangtze River gradually changed over time.Compared with the turning point of the control target in the water function zone,about 57.14%to 85.71%of the district turning points were consistent during the flood season,and the water quality of the mainstream of the Yangtze River could be judged continuously.The control objectives of the water function zone are close.In summary,from the perspective of spatial evolution,it can be assumed that the water quality of the mainstream of the Yangtze River tends to the control target of the water function zone.