黄土高原沟沿线的廊道防蚀效应探析

在分析黄土高原地区的沟沿线、沟沿线上下沟间地和沟谷地土壤侵蚀特征、小流域泥沙来源、坡沟侵蚀产沙关系的基础上,结合廊道的生态功能和以往的研究结果,认为在沟沿线的上部建立草灌与整地工程措施相结合的植物廊道,来拦蓄阻截沟间地的来水来沙,可使流域的土壤侵蚀量减少54．5%～77．0%。

我国区域土壤侵蚀与环境研究述评

区域土壤侵蚀与环境研究,是在比较大的中间尺度和较长的时间尺度上,对土壤侵蚀发生发展过程、土壤侵蚀因子、土壤侵蚀定量评价方法,以及土壤侵蚀治理对环境的影响进行研究的科学与技术体系。该领域的研究,即能直接为国家水土保持宏观决策提供支持,又能揭示土壤侵蚀的宏观规律,并于全球变化研究相联系。我国在该领域的研究主要概括四个方面,包括:①区域土壤侵蚀因子研究,是为认识土壤侵蚀环境特征和进行土壤侵蚀定量评价的基础,②区域土壤侵蚀评价研究,包括调查制图、定性评价和定量评价等,是该研究服务于水土保持实践的基本途径;③水土保持的环境效应研究,是从另外一个视角对土壤侵蚀环境与水土流失及其治理关系的认识。是确切评估水土保持效益,保证水土保持工作健康持续稳定发展的基础。今后应尽快开发区域水土流失定量评价模型,并在区域尺度上对环境效应的方式、范围、程度和发展趋势做出综合计价和分析预测。

ANUDEM和TIN两种建立DEM方法的对比研究

针对流域水文和土壤侵蚀定量模拟分析需要,对基于TIN和Hutchinson方法建立的DEM表现地形形态和起伏的能力进行了对比研究。结果表明,基于TIN建立的DEM始终存在一些平顶现象,一些较小的侵蚀沟被忽略,其上提取的河流不完全连续,多处出现多重线条河流,因而不能如实地反映地形起伏的细部特征。而基于ANUDEM建立的DEM,其派生等高线的形状与输入等高线吻合较好,较好地表现了地形的形态和起伏,对地形和坡度的反映更加连续和光滑,其上提取的河流信息基本与地形图上的河流一致。

黄土区不同土地利用方式坡面土壤含水率的空间变异性研究

为掌握不同土地利用方式下坡面土壤含水率的空间分布特征及其变异规律,利用经典统计学方法对黄土高原水蚀风蚀交错带草地和农地坡面土壤含水率的空间变异性进行了对比研究。结果表明:草地和农地的土壤含水率均值在同一土层深度下差异极显著,但二者在垂直方向、坡长方向的变异程度均为中等变异程度;草地和农地坡面土壤含水率的垂直变化特征不同,前者为降低型,后者在100 cm以上为波动型,以下为稳定型;草地和农地坡面土壤含水率均随坡长的增加呈波浪式变化规律,整体上有增加趋势;将坡面划分为5个坡长或将土层划分为4层以后,草地和农地坡面土壤含水率沿垂直方向、坡长方向的总体变化趋势均没有改变,但由于尺度的扩展获得了一些较大尺度上的水分信息。

子午岭地区林地破坏加速侵蚀对土壤养分流失和微生物的影响研究

以浅沟集水区为研究对象,分析了子午岭地区林地被开垦破坏15年后裸露地在不同侵蚀强度和侵蚀方式下的土壤养分流失和土壤微生物数量的变化。结果表明,林地开垦破坏后,土壤侵蚀加剧发展,侵蚀强度达159.7t/(hm2.a),是林地土壤侵蚀量的上千倍。开垦破坏15年后,裸露地浅沟集水区不同地形部位表层土壤全氮、有机碳、速效磷和土壤微生物总数显著减少,同林地相比,依次分别减少37.9%~82.6%、42.7%~86.4%、24.2%~80.3%和31.8%9~2.0%。在裸露地浅沟集水区梁坡随坡长的增加,表层土壤有机碳、全氮和速效磷含量及微生物总数呈显著的下降趋势,且沟槽的土壤各养分含量及微生物总数明显低于沟间。裸露地浅沟集水区土壤养分流失强度及微生物数量减少幅度在浅沟集水区的空间分布与土壤侵蚀方式和侵蚀强度相对应。林地开垦破坏15年后,土壤养分以有机碳流失最严重,其次分别为速效磷、全氮;微生物中的真菌减少幅度最大,细菌次之,放线菌减少幅度最小。

区域水土流失植被因子的遥感提取

NDVI是区域土壤侵蚀评价的最佳植被因子。基于遥感影像TM数据提取了NDVI值并将其与土地利用信息同时集成于土壤侵蚀图的每个图斑,建立了包含多种因子的空间数据库。通过每个图斑林草地面积百分比和NDVI值的统计分析,建立了NDVI与植被盖度的线性关系。多重因子数据库和NDVI-植被盖度关系,可以为区域土壤侵蚀定量评价提供支持。

区域水土流失研究的科学体系

区域水土流失研究是土壤侵蚀水土保持学科的重要组成部分。在综述国内外研究的基础上,从研究对象、研究目标和主要研究内容等方面,对区域水土流失研究的学科体系进行了讨论。最后提出了区域水土流失研究的重点问题,包括:区域水土流失及动态分析与趋势预测,水土保持的区域环境效应研究,区域水土保持政策与决策,区域水土保持的基础信息设施研究等四个方面。

WEPP模型的最新研究进展

WEPP(Water Soil Loss Equation)作为新一代水蚀预报模型,是指导水土保持措施优化配置、水土资源保护与持续利用的有效工具。近年来,遥感和GIS技术为WEPP快速获取所需资料、处理数据、图像编辑和输出等提供可靠的技术支撑;同时,区域化、尺度概念的引入,为WEPP应用于大尺度提供技术保障。为借鉴WEPP模型的优点,促进我国水蚀预报模型的发展,对WEPP模型的最新发展进行了详尽的介绍,并对WEPP应用到我国时可能存在的问题进行了初步分析。

Impacts of socio-economic factors on sediment yield in the Upper Yangtze River

In recent years, the role of human activities in changing sediment yield has become more apparent for the construction of hydraulic engineering and water conservation projections in the Upper Yangtze River, but it has not been evaluated at the macro scale. Taking Sichuan Province and Chongqing City as an example, this paper studies the relationship between socio-economic factors and sediment yield in the Upper Yangtze River based on section data in 1989 and 2007. The results show that sediment yield is significantly correlated with population density and cultivated area, in which the former appears to be more closely related to sediment yield. Moreover, in the relation of sediment yield vs. population density, a critical value of population density exists, below which the sediment yield increases with the increase of population density and over which the sediment yield increases with the decrease of population density. The phenomenon essentially reflects the influence of natural factors, such as topography, precipitation and soil property, and some human activities on sediment yield. The region with a higher population density than critical value is located in the east of the study area and is characterized by plains, hills and low mountains, whereas the opposite is located in the west and characterized by middle and high mountains. In the eastern region, more people live on the lands with a low slope where regional soil erosion is slight; therefore, sediment yield is negatively related with population density. In contrast, in the western region, the population tends to aggregate in the areas with abundant soil and water resources which usually lead to a higher intensity of natural erosion, and in turn, high-intensity agricultural practices in these areas may further strengthen local soil erosion. It is also found that population tends to move from the areas with bad environment and high sediment yield to the areas with more comfortable environment and less sediment yield. The natural factors have greater influence on sediment yield of western region than that of eastern region. Generally, the natural factors play a dominant role on sediment yield in the Upper Yangtze River.

Morphological Adaptations to Drought and Reproductive Strategy of the Moss Syntrichia caninervis in the Gurbantunggut Desert, China

The biological soil crusts (BSCs) in the Gurbantunggut Desert, the largest fixed and semi-fixed desert in China, feature moss-dominated BSCs, which play an indispensable role in sand fixation. Syntrichia caninervis Mitt. (S. caninervis) serves as one of the most common species in BSCs in the desert. In this study we examined the morphological structure of S. caninervis from leafy gametophyte to protonema using light and scanning electron microscopy (SEM). We also examined the relationships between the morphological structure of S. caninervis and environmental factors. We found that: (1) this moss species is commonly tufted on the sand surface, and its leaves are folded upwards and twisted around the stem under dry conditions; (2) the cells on both upper and lower leaf surfaces have C-shaped dark papillae, which may reflect sunlight to reduce the damage from high temperature; (3) the leaf costa is excurrent, forming an awn with forked teeth; and (4) the protonema cells are small and thickset with thick cell walls and the cytoplasm is highly concentrated with a small vacuole. In addition, we also found that the protonema cells always form pouches on the tip of the mother cells during the process of cell polarization. Our results suggest that S. caninervis has, through its life cycle, several morphological and structural characteristics to adapt to dry environmental conditions. These morphological features of S. caninervis may also be found in other deserts in the world due to the world-wide distribution of the species.

Self-assembly morphology effects on the crystallization of semicrystalline block copolymer thin film

Self-assembly morphology effects on the crystalline behavior of asymmetric semicrystalline block copolymer polystyrene-block-poly(L-lactic acid) thin film were investigated. Firstly, a series of distinctive self-assembly aggregates, from spherical to ellipsoid and rhombic lamellar micelles (two different kinds of rhombic micelles, defined as rhomb 1 and rhomb 2) was prepared by means of promoting the solvent selectivity. Then, the effects of these self-assembly aggregates on crystallization at the early stage of film evolution were investigated by in situ hot stage atomic force microscopy. Heterogeneous nucleation initiated from the spherical micelles and dendrites with flat on crystals appeared with increasing temperature. At high temperature, protruding structures were observed due to the thickening of the flat-on crystals and finally more thermodynamically stable crystallization formed. Annealing the rhombic lamellar micelles resulted in different phenomena. Turtle-shell-like crystalline structure initiated from the periphery of the rhombic micelle 1 and spread over the whole film surface in the presence of mostly noncrystalline domain interior. Erosion and small hole appeared at the surface of the rhombic lamellar micelle 2; no crystallization like that in rhomb 1 occurred. It indicated that the chain-folding degree was different in these two micelles, which resulted in different annealing behaviors.

Distribution of uranium isotopes in the main channel of Yellow river (Huanghe), China

Uranium isotopes were measured in waters and suspended particulate matters (SPM) of the main channel of Yellow River, China that were sampled during four field trips between August 2005 and July 2006. The results show that the concentration of dissolved U (2.04-7.83 mu g/l) and the activity ratio of U-234/U-238 (1.36-1.67) are much higher than the average U concentrations and activity ratios of global major rivers. Mass balance calculations using the results of simulated experiments and measurement data show that the section of the Yellow River between Lanzhou and Sanmenxia has its dissolved U derived from two sources: suspended sediments (68%) and groundwater/runoff from loess deposits (32%). Both sources are related to the heavy erosion of the Chinese Loess Plateau. (C) 2008 Elsevier Ltd. All rights reserved.