| As China's largest freshwater lake and important part of the Yangtze river basin, the Poyang lake basin plays an extremely important role in flood control, water and soil conservation, biodiversity conservation and ecological security maintenance in the middle and lower reaches of Yangtze River. In this paper, the implementation of the "river-mountain-lake comprehensive development and governance project in Jiangxi province" is set as a background, and the increase of forest coverage rate and the improvement of forest quality in Poyang lake basin is summarized as well. Then on this basis, the 2000 years is as a turning point, the base flow and its coefficients which flow in and out the Poyang lake, as well as the lake inflow and outflow in dry season before and after 2000 years are calculated according to the hydrological years, meanwhile the change of sediment is analyzed by using the rainfall and runoff data in this basin from 1953 to 2012. That is to say, based on the microscopic mechanism research, the macro impacts of hydrological processes and soil and water loss in the basin on account of the change of forest landscape for many years in Poyang lake basin are quantitative analyzed from the perspective of watershed ecology.The natural precipitation in Poyang lake basin has no tendency change over the past 60 years. The coverage rate of forest in this basin is increased from 31.5% to 63.1%, the forest quality is improved greatly as well. The average base flow weighting coefficient of five rivers(Xiu river, Rao river, Fu river, Ganjiang river and Xinjiang river) is 0.179 from 1953 to 1999 and 0.227 from 2000 to 2012, showed a trend of increase. Apparently, the river base flow is increased 170 m3/s, and the 80 m3/s of it is the contribution of forest. From 2000 to 2012, the average rainfall in Poyang lake is less than the average rainfall from 1953 to 2012 2.61%, the lake average inflow and outflow rate reduced by3.11% and by 1.76%respectively, and the amount of water in average water season tend to be low than before. The hydrological process of this basin is changed in some degree before and after 2000, and the specific changes are as follows: firstly, in wet season, the rainfall is decreased by 6.19% after 2000 years, the runoff from five rivers(Xiu river, Rao river, Fu river, Ganjiang river and Xinjiang river) into the Poyang lake is 9.93% less than before 2000, and the lake outflow is also reduced by 6.87%, therefore, the flood risk is eased to a certain extent. Secondly, the corresponding data are raised by7.45%, 12.5%, 8.02% respectively in the dry season which is beneficial to the water use of production, the living and ecology. What's more, 2001 years later, the sand quantity of entering a lake reduce 1007x104 t per year on average, but the sand quantity of escaping a lake is increased 314×104t per year. As a result, the Poyang lake channel is transformed from siltation into erosion. The results indicate that, if the river base flow is used as connection point, the micro mechanism such as the improvement in vegetation conditions and the increase of forest coverage rate make contributions to the redistribution of natural rainfall and the reduction of surface soil erosion can be regarded as macro performance of the change in river lake hydrological processes.The current research shows that the research of watershed ecology mainly quantitative analysis how the factors such as small watershed vegetation, land use, soil structure and geological conditions affect the precipitation, evaporation, soil moisture content, surface runoff and underground runoff. However, how these micro-mechanism impact the macro hydrological processes are rarely studied, especially the change of forest coverage in large river basin. In this paper, based on the microscopic mechanism research, and put the river base flow as connection point, the macro impacts of hydrological processes in the basin on account of the change of forest landscape in Poyang lake basin are quantitative analyzed by using the rainfall, runoff and soil erosion data in this basin from 1953 to 2012. Theoretically, this research method is an innovation.In the past, many experts believe that the lake average inflow reduce is one of the main reason of the dry season in advance and longer and the extreme low water level is lower. This paper shows that, the lake inflow and outflow are increased on account of the increase of the forest coverage, the improvement of the forest quality and the construction of water projects. In this paper, lots of detailed analysis and contrast are listed, and the argument is sufficient. Therefore, this paper has great practical value. |
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