Study Of Water System Connectivity And Its Influence On Water Quality In Chaohu River Basin

Chaohu,one of the five largest freshwater lakes in China,plays an important role in the social and economic development.In recent years,with the rapid development of industrial economy in Chaohu River Basin,the process of urbanization in rural areas is accelerating,and the deterioration of water quality in the region is serious.The water environment quality,water ecological health and water security are more and more low,and the connectivity of river network is an important factor to restrict the water environment quality and social economic development.In river network density decreased sharply,river structure tends to be simple,flood disasters and deterioration of water quality situation intensified,seriously affecting the harmonious relationship between people and water,its modernization and sustainable development is restricted to a great extent.This paper selects the Chaohu River Basin as the research object.Current studies evaluate water system connectivity by using some index based on water flow resistance and graph theory,hydrological process,or water system pattern.In this paper,the calculation method of water system connectivity based on water flow resistance and graph theory is modified,the calculation formula of hydrologic connectivity based on hydrological process is improved,and drainage pattern connected degree is obtained by summarizing the main indicator of river network connectivity.On this basis,index system is built to evaluate water system connectivity of Chaohu River Basin.On the macro-scale,the Chaohu river basin is divided into 25 hydrological and ecological units according to the characteristics of Chaohu River Basin.And we use the index system to quantitatively evaluate the connectivity of different ecological units;Three hydrological sections were selected for each hydrological unit,and the spatial distribution of water quality was obtained by the comprehensive index method of water quality.The water quality of water quality was analyzed by SPSS correlation analysis;At the micro scale,the water system of the Chaohu river basin is selected as the research object,and the different connectivity schemes and the connectivity of the water system are determined.The main research contents and results are as follows:(1)Water connectivity evaluation.From the angle of physics and mathematics,the evaluation index system of river connectivity criterion layer is based on the connectivity of flow resistance and graph theory,considering the network connection channel shape parameters,hydraulic gradient and roughness coefficient will affect the different types of the actual river water conveyance capacity,so choosing stream connectivity as the index layer;From the perspective of hydrology,the criterion layer is the hydrological connectivity of the whole region,which reflects the relationship between the connectivity of the network and the local rainfall runoff,and the improved hydrological connectivity as the index layer;From the geographical point of view,the criterion layer is the connection degree of the water system pattern in the region,and the distribution of the river network pattern is mainly considered.Based on the flow resistance and graph theory,the index of river water connectivity,the various indexes of hydrological processes and the weighted average of the river system pattern are obtained.(2)Spatial distribution of water quality in Chaohu River basin.According to the water quality test results of 6 indicators including nitrogen oxides,nitrate,phosphate,total phosphorus,total nitrogen,chemical oxygen demand of 75 sections of Chaohu River Basin in 2011,through principal component analysis method to evaluate the water quality of each river section,the water quality of water quality for the 3 sections of each hydrological unit of average value is each hydrologic unit,drawing the evaluation results of spatial distribution of water quality in 2011.(3)Study on the relationship between water quality and water quality in macro-scale.SPSS correlation analysis was used to analyze the relationship between water connectivity,hydrological connectivity,connectivity of water system pattern,water system connectivity and water quality.The results show that the stream connectivity and water pattern connectivity effects on water quality are larger and weaker hydrological processes and water quality correlation coefficient,but the overall system connectivity and quality strong correlation.(4)Study on the relationship between water quality and water quality in micro-scale.Select the Baishitian River Basin as the research object,according to the Lujiang county has not communicated,put forward the design scheme that not connected,little connected and big connected.With the help of the MIKE11 model,the concentrations of total nitrogen and total phosphorus were obtained of the three schemes,analysis of pollutant concentration changes of different communication schemes Baishitian River Basin,in the micro scale analysis of the impact of river connectivity on water quality.The results show that the connectivity of river system plays a positive role in improving water quality.