| There are plenty of function of reservoir in north raid region, such as flood control, irrigation and urban water supply etc. It has great significance that study the control of eutrophication in these reservoirs due to the shortage of natural runoff, the impact of high capacity of pollutant and the occurrence of eutrophication occasionally. In this paper, Fenhe Reservoir is served as a research carrier, coupling model of eutrophication is built by combining hydrodynamic model, substance transport and diffusion model and the life course of eutrophication; Proceeding from actual hydrology, climate and weather,the mechanism evolution of eutrophication in Fenhe reservoir is acquired by simulative analyzing the transport and diffusion laws and temporal spatial distribution of the factors like chlorophyll a, transparency, total nitrogen and total phosphorus. The research achievements have a certain significance in theoretical and practical.The research achievements are as follows:(1) According to the similarity of reservoir in north raid region,systematized ways of thinking, GIS technique for boundary digitalizing and triangular mesh for establishing the planar grid system are used. The document about depth of water were difference value acquired and imported, meanwhilethe digital terrain model were inserted within triangle and extended of boundary;Then time series is different acquired; After that, hydrodynamic model and substance transport and diffusion model were coupled first, then coupled a series of complex life course of eutrophication, the reservoir coupling model of eutrophication is finally generated. A technology system, which studies quantitatively the problems of eutrophication in reservoir, were formed by optimum combination of parameter which acquired by calibrating and verifying the parameter of model through the measured data and analyzing the diffusion and temporal-spatial distribution discipline of all kinds of nutrient.(2) Analyzing and confirming the wind and inlet and outlet water as the main hydrodynamic impact factor; Homologous time series is acquired by interpolation and reservoir hydrodynamic simulation is made using regional meteorological data, inflow of reservoir and actual operational states of reservoir;Total nitrogen(TN), total phosphorus(TP), chlorophyll a(Chl-a) and transparency(SD) are chosen as output factors, which is used as simulating the eutrophication of reservoir, meanwhile calibrating and verifying the parameter of model through the measured data.(3) The results of hydrodynamic simulation: 1) Different inflow condition only have distinct influence on flow velocity of reservoir entrance; 2)It is evident that the flow velocity and direction of downstream and the area around dam is influenced by whether draw off of a reservoir; 3) Wind field has a great influence up on reservoir flow velocity and direction. In calm, the reservoirflow velocity is slow and has little difference in direction; While in southwester and northwester, the flow velocity is accelerated obviously and difference in direction become larger; 4) The flow velocity under northwester is higher than the one under southwester; 5) the circumflux is formed more easily in a wider area of reservoir, which has a higher flow velocity than other areas. As a conclusion, the key driving factor of hydrodynamic status is the condition of wind field. The main flow form is the wind-driven flow.(4) The results of simulation analysis of eutrophication: 1) The concentration of chlorophyll had been rose since March, and achieved peak on July and August. It had been transitory fluctuated during that period. After September, the concentration of chlorophyll decreased along with decrease of temperature; 2) The concentration of TN and TP had been decreased obviously around May, while the concentration of nutrient had not decreased and reached peak during July to August; When came to October, the concentration of nitrogen and phosphorus decreased again, however, rose because of the death and decomposition of phytoplankton in November; After that, the concentration of TN and TP changed slight but still present the situation of decrease; 3) In the same condition of inlet and outlet, the transport and diffusion of the nutrient are different due to various wind direction and the diffusion velocity is lower in order southwester, northwester and calm. 4) The transparency of reservoir increased due to wash and purification by flow from upstream, while the water quality became worse because of importing of high concentration of nutrient,especially in the region of middle and upper reaches. 5) When the high concentration of nutrient importing the reservoir, the pollutant in central zone diffused more faster and dilute diffusion range is smaller than that in both sides,therefore, the water quality in central zone is higher than that both sides.(5) According to simulation factors, the evaluation model was built, the grading standard was confirmed, the condition of nutrition of each feature points were calculated and finally the state of nutrition evaluation figure for the whole reservoir was generated, results are as follow: during the period of December to March, Fenhe reservoir kept the condition of mesotrophic, especially in downstream; The condition of other period was worse, especially middle and upper reaches which kept low-grade eutrophic during April to June and October to November; July and August had the worst state yearly, when some area in middle and upper reaches occurred apparently moderate eutrophication.According to nutrient, hydrology, climate and weather, analyzing the mechanism of eutrophication in reservoir. During the process of eutrophication in Fenhe reservoir, the three kinds of most influencing driven factors is water temperature,wind field and condition of inlet and outlet, the primary endogenous limiting factor is P which the concentration of P is 1 to 5 times than international P load standard in reservoir(0.02mg/L).This paper combining hydrodynamic model, substance transport and diffusion model and the complex life course to build eutrophication coupling model. Four kinds of representative factors were chosen to simulate the state ofeutrophication in Fenhe reservoir and comprehensive nutrition state index was used to evaluate and analyze in all directions from time and space. The results of this research had some new ideas and reference value in pollution and eutrophication control in Fenhe reservoir. |
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