| Loess Plateau is the most influenced area of China's water and soil loss region, especially in the hilly area of Loess Plateau. The serious water and soil loss not only worsens the very fragile ecological environment but also restricts the local ecological and socio-economic sustainable development.In this thesis, the representative basins of the hilly area of Loess Plateau were the investigated as objects, including Wuding River Basin, Yan River Basin and Qingjian River Basin.At first, according to the long-term (1960-2009) observation hydrological data obtained from the hydrological stations, different periods of Land Use Data (1985,1995,2000 and 2008), the runoff and sediment properties of the above three basins were analyzed spatio-temporally, which use the qualitative, quantitative and mathematical statistics analysis, GIS and RS spatial analysis techniques with the help of Landscape Ecology and quantitative ecology methods.Second, taking the ecological restoration of loess plateau as the background, the dynamic transfer of the land utilization and the spatio-temporal evolution of landscape pattern were analyzed on the basin scale. On this basis, the impact of evolution of land use pattern on the change of runoff and sediment process was further explored, and the land cover pattern process of the variation of runoff and sediment basin was also revealed.The study provides the theoretical foundation and the decision-making basis for the optimal allocation of water resources and the effectively improvement of the regional ecological environment of China's Loess Plateau. The main conclusions are listed as follows:(1) The obvious heterogeneity existed in the time-varying process of the runoff and sediment in the hilly area of Loess Plateau and its spatial difference was significant. The Analysis shows that the annual runoff and sediment distributions in Yan River Basin and Qing Jian River Basin were single peak curves, while these of Wu ding River Basin were a single peak curve and a double peak curve, respectively.(2) The inter-annual spatio-temporal variations of the runoff and sediment were significant and the divergences between different basins at different ecological restoration times were different. The analysis shows that annual changes of the average flow and annual sediment load in the hilly area of Loess Plateau were in the downward trend. The reduction rates of water and sediment varies with time and space. The characteristic periods of the sediment runoff evolution were the years after 1980s and after 2000. The flow reduction of Yan River Basin was more obvious. Additionally, the flow reduction and the amplitude of the reduction of Wu ding River Basin were much larger. The relation between runoff and sediment was close and the fitting curves varied with different basins and their runoff characteristics.(3) Taking the ecological restoration as the background, the different types of land use transformed frequently, in which farmland to forestland and the grassland transformation were the main forms. In different basins, not only the transformation of farmland but also the newly increase of forestland and grassland were apparent, and the transformation entered the accelerated period after 2000. Driven by the vegetation, the spatial drift of the land use focus was obvious and the trajectory demonstrated that the focus of farmland shifted to the east, forestland to the northwest and grassland to the north.(4) Driven by the ecological restoration, land use and its spatial and temporal dynamics resulted in the significant changes of the landscape pattern. At the pattern class level, the characteristic changes of farmland, forestland and grassland were more obvious, compared with the water area, urban, mining and construction land. The ecological restoration increased not only the landscape fragmentation level of farmland and forestland, but also the complexity of forestland characteristics. With the implementation of the Grain for Green Project, the proportion of the average farmland area continued dropping. On the contrary, the grassland increased. The degree of fragmentation of different basins rose overall at landscape level, while landscape connectivity was reduced continuously. In addition, the landscape diversity (SHDI) of Qing jian River Basin showed a downward trend overall, while Yan River Basin were on the rise. Land use and vegetation restoration of structural adjustment had led some type of landscape dominance growing and landscape evenness degree constantly decreasing, and both developed towards to a single landscape type.(5) The relationship between the relative situation of land use pattern and the time-varying water and sediment processes were closed on the basin scale. The analysis shows that farmland was not only the core landscape element of land use in the hilly area of Loess Plateau, but also the main source area of soil erosion and sediment. With the area as the core predictive factor of land use, the impact of the 4-year average density of runoff and sediment yield on the time-varying response degree of land use was maximum.(6) Different landscape types had different density of runoff affecting factors, among which the spatial adjacency of farmland, forestland, grasslands patches and the size of core patch area were the common factors which influenced the density of runoff. The impact of the characteristics index of farmland patch on runoff and sediment processes was the biggest, followed by grassland, and forestland was the minimum. However, the predictive ability of the impact of patch characteristics of farmland, forestland and grassland on the sediment transport was higher than that of the runoff process. In the landscape level, the characteristic index impacting of runoff and sediment process differed in different revegetation period. In addition, there was always a significant positive correlation between landscape edge density, landscape connectivity, the runoff density of runoff and sediment yield.(7) The spatio-temporal relations between landscape pattern and sediment runoff process, dominated by the farmland, forestland and grasslands, were very intense. The analysis indicates that landscape pattern change of farmland played an important role in the process of the runoff and sediment variation, but with the implementation and the advancement of the Grain for Green Project, its indicative function was gradually replaced by the landscape patterns of forestland and grassland.(8) The benefits from water and sediment reduction were obvious in the hilly area of Loess Plateau driven by the Grain for Green Project. The studies shows that the average sediment yield reduced by 54% and the average density of runoff decreased by 15% in the recent nine years. |
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