| Through the on-site water sample collection,detection and analysis of pollution index concentration in the three main inflow rivers of the upstream section of Dahuofang Reservoir,the influence of season on water quality index is studied,and the water quality of three typical monitoring sections in the study area is evaluated.According to the evaluation results,three kinds of aquatic plants are selected to carry out water purification simulation experiments to analyze the purification effects of different aquatic plants on pollution indicators.The main research results are as follows:(1)A total of 13 monitoring points are set up in the three main rivers in the upstream section of Dahuofang Reservoir.Water quality status of the studied area is obtained by laboratory testing: the total phosphorus concentration of all monitoring points have reached the national surface water category ? or above standards;the total nitrogen concentrations all exceed the national surface water category ? standards,which seriously exceed the drinking water requirements.And the COD and permanganate index concentrations of two sampling points on Hunhe River are class ? standards,the COD concentrations of the remaining eleven monitoring points all meet the surface water class ? standard,and the permanganate index concentration reaches the surface water class ? standard.(2)Total phosphorus,total nitrogen,chemical oxygen demand and permanganate index of Beizamu section,Gulou section and Taigou section are related to seasonal changes.Among them,the concentration of TP,TN and COD is higher in winter,and the concentration of permanganate index is higher in summer.(3)The traditional comprehensive water quality index method is improved in this paper.The main and objective weights of water quality indicators are obtained by AHP and CRITIC methods respectively,and the combined weights are calculated by the ideal point method.The improved evaluation method is used to evaluate the water quality of the study area.The evaluation results show that: from 2011 to 2017,The comprehensive water quality grade of Beizamu section is class ?~?,the Gulou and Taigou section are surface water Class ? standards.In the seven years,the Beizamu section has not reached the water environmental function zoning requirements in the area for 3 years,and all the years of the Gulou and Taigou section are not meet the water environment functional zoning requirements in the area.At the same time,the total nitrogen index in the upstream section of the Dahuofang Reservoir exceed the standard seriously,which has exceeded the surface water class ? standard and affect the overall water quality level.(4)Three kinds of aquatic plants are used to carry out water purification simulation experiments in upstream section of Dahuofang Reservoir.The results show that: the purification effects of three aquatic plants on total phosphorus are eichhornia crassipes =ceratophyllum demersum > reed,and the removal rate of total nitrogen is from large to small for reed > eichhornia crassipes > ceratophyllum demersum,the removal effect of COD isreed > eichhornia crassipes > ceratophyllum demersum.In the different combinations of aquatic plants,the combination of reed,eichhornia crassipes and ceratophyllum demersum has the best purification effect.From the perspective of plant biomass change,the biomass of eichhornia crassipes increases the most.Considering the purification effect of plants and the "crazy" problem that may occur by eichhornia crassipes,it is believed that reed is the most suitable aquatic plant with the study area.It can be combined with ceratophyllum demersum,which has the function of restraining algae growth to achieve better integrated control aim.For eichhornia crassipes,it is should be used with caution. |
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