Wen Anbang

Soil conservation and sustainable eco-environment in the Loess Plateau of China

The Loess Plateau is well known to the world because of its thick loess and severe soil erosion. Loess is a highly erosion-prone soil that is considerably susceptible to water erosion. The Loess Plateau also has a long cultivation history, hence population growth, vegetation degeneration serious soil and water loss were obviously problems on Loess Plateau. This article analyzes several strategies of soil and water conservation on the Loess Plateau, such as terracing, planting trees, natural vegetation rehabilitation and construction of warp land dams. Different periods had different strategies of soil and water conservation and each strategy had its characteristics and effects. Finally, the research directions and future perspectives of the Loess Plateau were discussed, including the strategies of sustainable eco-environment of Loess Plateau in China.

Influencing factors of sediment deposition and their spatial variability in riparian zone of the Three Gorges Reservoir, China

Many factors can affect the sediment deposition and soil erosion process in riparian zone, including terrain, sediment transport and water level fluctuations. Clarifying the factors influencing sediment deposition process in the riparian zone of the Three Gorges Reservoirs is an important problem to determine the key area of sediment deposition and its trend of development in the study area. In order to reveal the influence of these environmental factors on the sediment deposition in riparian zone of the Three Gorges Reservoir, this study investigated 1) the amount of deposited sediment in different environmental conditions, 2) the potential factors affecting sediment deposition in riparian zone of the Three Gorges Reservoir, 3) the relationship between the deposited sediment amount and these factors previously mentioned using correlation analysis, and 4) the influence of human activities considered as an additional factor. This study found that 1) slope gradient, elevation, inundating duration and human activities were the main factors influencing sedimentation in riparian zone of the Three Gorges Reservoir, and 2) the impact of each factor varied with spaces. Specifically, in the upper reach from Jiangjin to Fuling, human activities such as gravel dredging, bank revetment and ports and wharfs constructing disturbed considerable amounts of deposited sediment, as a result, there was no natural law to dictate the distribution. In the middle reach from Fuling to Fengjie, slope gradient and inundating duration were the controlling factors, and the sediment deposition amount was greater in the areas with a gentler slope or lower elevation. Water flow on gentler slopes generally had lower velocity, resulting in more sediment to deposit. Sites with lower elevations would be drowned by sediment-laden flow with a longer duration resulting from hydrologic regime controlled by the operating strategy of the Three Gorges Reservoir, leading to a larger amount of sediment deposition. In the lower reach from Fengjie to Zigui, slope gradient was similar to the middle reach, performing a primary factor, while other factors showed little relationship with sediment amount.

Using 137Cs tracing methods to estimate soil redistribution rates and to construct a sediment budget for a small agricultural catchment in the three gorges reservoir region, China

Soil erosion and associated off-site sedimentation are threatening the sustainable use of the Three Gorges Dam. To initiate management intervention to reduce sediment yields, there is an increasing need for reliable information on soil erosion in the Three Gorges Reservoir Region (TGRR). The purpose of this study is to use 137Cs tracing methods to construct a sediment budget for a small agricultural catchment in the TGRR. Cores were taken from a pond and from paddy fields, for 137Cs measurements. The results show that the average sedimentation rate in the pond since 1963 is 1.50 g cm−2 yr−1 and the corresponding amount of sediment deposited is 1,553 t. The surface erosion rate for the sloping cultivated lands and the sedimentation rate in the paddy fields were estimated to be 3,770 t km−2 yr−1 and 2,600 t km−2 yr−1, respectively. Based on the estimated erosion and deposition rates, and the area of each unit, the post 1970 sediment budget for the catchment has been constructed. A sediment delivery ratio of 0.5 has been estimated for the past 42 years. The data indicate that the sloping cultivated lands are the primary sediment source areas, and that the paddy fields are deposition zones. The typical land use pattern (with the upper parts characterized by sloping cultivated land and the lower parts by paddy fields) plays an important role in reducing sediment yield from agricultural catchments in the TGRR. A 137Cs profile for the sediment deposited in a pond is shown to provide an effective means of estimating the land surface erosion rate in the upstream catchment.

137Cs and 210Pbex as soil erosion tracers in the hilly Sichuan Basin and the Three Gorges area of China

Accelerated soil erosion and land degradation represent major environmental problems for agricultural lands. Reliable information on the rates of soil loss is urgently needed. The traditional techniques for documenting rates of soil loss may meet this need, but face many limitations. The fallout radionuclides, especially 137Cs and 210Pbex, are increasingly used as effective tracers to quantify soil erosion rates, and they represent a valuable complement to the existing classical methods. This paper aims to introduce the basis for assessing soil erosion rates on cultivated and uncultivated slopes by using 137Cs and 210Pbex measurements, to compare the 137Cs and 210Pbex reference inventories, and to report several case studies undertaken in the hilly area of Sichuan Basin and the Three Gorges area of China.

137Cs finger printing technique for erosion and sedimentation studies

Abstract137Cs is an artificial radionuclide with a half -life of 30.2 years, which was released into the environment as a byproduct of atmospheric testing of nuclear weapons during the period of 1950s to 1970s with a peak deposition in 1963. 137Cs fallout was strongly and rapidly adsorbed by soil particles when it deposited on the ground mostly with precipitation. Its following movements will associate with the adsorbed particles. 137Cs tracing technique has been widely used in soil erosion and sedimentation studies since 1980s. This paper introduces the basis of the technique and shows several case studies of assessment of soil erosion rates, investigation of sediment sources and dating of reservoir deposits by using the technique in the Loess Plateau and the Upper Yangtze River Basin.