| The Three Gorges Project is the world’s largest hydro-junction,and the bond that connects to the middle and lower reaches of the Yangtze river in the upper Yangtze river valley.It is not only the ecological barrier betweenthe middle and lower reaches of the Yangtze river region,and also exerting the benefit on the flood control,navigation,power generation and ecological comprehensive effect.With running and the impoundment of the Three Gorges Reservoir and the fast development of social economy,a series of ecological environment problems happened in the Three Gorges Reservoir Area.This influenced and restricted the function of water and the use of water resources.This article selects Pengxi River Basin as the study area,to study the dynamic changes of spatial and temporal distribution of water quality,algae blooms by building a three-dimensional water quality and ecological model in Pengxi River basin.It will show great significance on the protection of ecological environment and realize ecological civilization for the Three Gorges Reservoir Area.The research results are as follows:(1)To meet the needs of water environment management of the Three Gorges Reservoir,the present situation of the Three Gorges Reservoir Area,the mechanism research of water blooms and water environment models in the Three Gorges Reservoir Area were detailed summarized.The results showed that in situ observations or laboratory experiment methods are hard to reflect the dynamic changes of water quality,hydrology and algae process,so a set of three-dimensional water quality of river basin water ecological model covering land-main stream-tributaries is necessarily needed.(2)Based on mature hydrodynamic model and non-point source model in Pengxi River,this article builded a three-dimensional water quality and ecological model.Measured TN,TP,COD and NH3-N,Chla data from January to December,2013 were used to calibrate model parameters.Model validation of February to July,2016 results show that the error is less than 30%and accuracy can reach 90%.The simulated values and measured values are in good agreement,so the model has high simulation precision and can be used in predicting water quality and algal in Pengxi River.(3)The history monitoring data from 2008 to 2013 and the monitoring data from 2013 to 2015 in Pengxi River showed that:TN and TP concentration values are more than the internationally recognized the occurrence of eutrophication levels which demonstates that the river has enough nutrients for algal blooms.In the period of high water level of Three Gorges Reservoir,the eutrophication index shows the lowest,while in the drainage period and low water level period,the eutrophication index keeps the highest;The concentrations of TN and TP in Pengxi River are lower than the Yangtze river,and the concentrations increases from upstream to downstream.(4)Based on the three-dimensional basin water environment model built in the Pengxi River,this article simulated the water quality and ecological status to study the spatial distribution characteristics of water quality indicators and the vertical distribution characteristics of Chla in different water periods.The results showed that:the concentrations of TN,TP and NH3-N in the Yangtze river are higher than in Pengxi River,while concentrations of COD and Chla are on the contrary.The vertical distribution characteristics of Chla concentration differ significantly.Generally,it is high on the surface and much low at the bottom.With the increase of the water level in the Three Gorges Reservoir,The length and scope of the flow backward gradually increase. |
