Zhang Xinbao

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.

SLOPE LITHOLOGIC PROPERTY, SOIL MOISTURE CONDITION AND REVEGETATION IN DRY-HOT VALLEY OF JINSHA RIVER

The dry-hot valley of the Jinsha River is one of the typical eco-fragile areas in Southwest China, as well as a focus of revegetation study in the upper and middle reaches of the Changjiang River. Due to its extremely dry and hot climate, severely degraded vegetation and the intense soil and water loss, there are extreme difficulties in vegetation restoration in this area and no great breakthrough has ever been achieved on studies of revegetation over the last several decades. Through over ten years’ research conducted in the typical areas—the Yuanmou dry-hot valley, the authors found that the lithologic property is one of the crucial factors determining soil moisture conditions and vegetation types in the dry-hot valley, and the rainfall infiltration capability is also one of the key factors affecting the tree growth. Then the revegetation zoning based on different slopes was conducted and revegetation patterns for different zones were proposed.

Interpreting sedimentation dynamics at Longxi catchment in the Three Gorges Area, China, using Cs-137 activity, particle size and rainfall erosivity

Reservoir sedimentation dynamics were interpreted using Cs-137 activity, particle size and rainfall erosivity analysis in conjunction with sediment profile coring. Two sediment cores were retrieved from the Changshou reservoir of Chongqing, which was dammed in 1956 at the outlet of Longxi catchment in the Three Gorges Area using a gravity corer equipped with an acrylic tube with an inner diameter of 6 cm. The extracted cores were sectioned at 2 cm intervals. All sediment core samples were dried, sieved (<2 mm) and weighed. 137Cs activity was measured by γ-ray spectrometry. The particle size of the core samples was measured using laser particle size granulometry. Rainfall erosivity was calculated using daily rainfall data from meteorological records and information on soil conservation history was collated to help interpret temporal sedimentation trends. The peak fallout of 137Cs in 1963 appeared at a depth of 84 cm in core A and 56 cm in core B. The peaks of sand contents were related to the peaks of rainfall erosivity which were recorded in 1982, 1989, 1998 and 2005, respectively. Sedimentation rates were calculated according to the sediment profile chronological controls of 1956, 1963, 1982, 1989, 1998 and 2005. The highest sedimentation rate was around 2.0 cm∙a-1 between 1982 and 1988 when the Chinese national reform and the Household Responsibility System were implemented, leading to accelerated soil erosion in the Longxi catchment. Since 1990s, and particularly since 2005, sedimentation rates clearly decreased, since a number of soil conservation programs have been carried out in the catchment. The combined use of 137Cs chronology, particle size and rainfall erosivity provided a simple basis for reconstructing reservoir sedimentation dynamics in the context of both physical processes and soil restoration. Its advantages include avoiding the need for full blown sediment yield reconstruction and the concomitant consideration of core correlation and corrections for autochthonous inputs and reservoir trap efficiency.

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.

A ~(210)Pb_(ex) mass balance model in cultivated soils in consideration of the radionuclide diffusion

The existing 210 Pb ex mass balance models for the assessment of cultivated soil erosion are based on an assumption that 210 Pb ex is quite evenly mixed within the plough layer.However,the amount of 210 Pb ex distributed in the soils below the plough depth,like a downward tail in the lower part of the 210 Pb ex profile,has been largely ignored.In fact,after the initial cultivation of undisturbed soils, 210 Pb ex will diffuse downward from plough layer to the plough pan layer due to the concentration gradient.Assuming 210 Pb ex inventory is constant,the depth distribution in the two layers of the cultivated soils will achieve a steady state after continuous cultivation for 10.37 years,when 210 Pb ex is evenly distributed in the soils of the plough layer with an exponential concentration decline with depth in the soils of the plough pan layer,and the 210 Pb ex concentration at any depth will be invariable with time.The work reported in this paper attempts to explain the formation of the 210 Pb ex tail in the soil profile below the plough depth by theoretical derivation of the 210 Pb ex depth distribution process in the two layers of the cultivated soils,propose a 210 Pb ex mass balance model considering 210 Pb ex diffusion based on the existing model,and discuss the influence of the 210 Pb ex tail to the existing model.