| Soil erosion has been recognized as amajor soil degradation process since it aversely affects soil quality by reducing infiltration rates, water-holding capacities, nutrients, organic matter, soil biota and soil depth. As such, soil erosion causes a reduction of soil productivity and a significant ecological damage by depleting soil biodiversity and affecting plant composition. The Three Gorge Project (TGP) of China necessitates the resettlement of over one million population (mostly farmers) to more rugged and isolated areas than their original settlements. Soil erosion is a key factor determining the ecological sustainability of such a resettlement scheme. If this problem is not adequately addressed, not only will the well being of the resettled people suffer, but the functionality of the Three-Gorge Dam and Reservoir will also be undermined due to siltation and eutrophication. The study of soil erosion and deposition law and its reasonable prediction have not only an important significance for ecological system construction and reconvertion, but also an effective tool for appraising rationality and validity of government's policies. In this dissertation, based on integrated on techniques and methods such as Geographical Information System, Remote sensing, runoff plot experiment and field surveying, with the theoretical support of Landscape Ecology and Soil Erosion, landscape pattern changes and responses of soil erosion in two typical watersheds were analyzed and discussed in detail. The main results are as follows:First, traditional researching methods of soil erosion in the field scale have its limits. With the researching scale change, soil erosion mechanisms are also different. Landscape is a higher level than ecological system in natural hierarchy model, and research of many lower level ecological problems will necessarily be integrated in this hierarchy. Soil erosion is an important approach for matter and energy flux in ecological system. Researching soil erosion in landscape scale will facilitate resolving some essential soil erosion mechanisms. Using theory of Landscape Ecology in soil erosion prediction and planning can help us understand soil and water loss approaches in ecological system, dynamic law in different landuse and its configuration. As a result, panner can effectively guide agricultural structure adjustment, design compositive control measures of soil erosion, and resolve soil erosion in integrated management.Second, approaches on multi-source data integration and multi-items databaseestablishment were discussed, including basic spatial resolution of pixel and scale in different watershed level used to research landscape patterns and assess soil erosion and deposition, organization of data layers and data items, data integration, data file management and metadata standard.Third, during the past 6 years, the landscape in the Letianxi watershed has undertook a comparative complex change of landscape structure and an apparent transition of landscape composition. Patch numbers decreased from 3812 to 3351, and average patch size increased 2ha. The reason is that sparse forest and shrub converted to forest, and new forest combining with original forest resulted in much larger forest patches. The analyses on landscape fragmentation at Letianxi watershed by patch density show that the patch density was smaller, and the landscape fragmentation was reduced. The decreasing value of shape, including AWMSI and AWMPFD shows patch shape become simple. However, these indexes of susceptive area, such as upland are increasing. The decreasing of Shannon's diversity index and evenness index and the increasing of contagion index manifest the landscape heterogeneity and landscape diversity was reduced.Fourth, from 1989 to 1995, the landscape in the Wangjiaqiao watershed is influence comprehensively by both natural factors and social-economic facrors. Patch numbers increased from 116 to 251, and average patch size decreased more than one half. The largest patch index (LPI) reduced... |
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