Effects of changes in land use and land cover on sediment discharge of runoff in a typical watershed in the hill and gully loess region of northwest China

Land use plays a much more important role than other factors, such as climate, soil properties, topographic features, vegetation coverage, human activities and others, in affecting soil erosion and sediment discharge. In order to understand the effects of changes in land use on sediment discharge and to provide a theoretical basis for land use planning, management and ecological restoration, we used the controlled Qiaozidong watershed and the uncontrolled Qiaozixi watershed in the third sub-region of the Loess Plateau as examples and analyzed the effects of land use and land cover on the discharge of sediments. The results show that the impact of land use and land cover on the annual amount of sediment discharge is significant. Compared with the uncontrolled watershed during similar periods, the amount of sediment discharged from the controlled watershed was reduced by 44%, 75% and 86%, respectively, in wet, normal and dry years. In the controlled watershed, compared with the period from 1986 to 1994, the amount of sediments discharged was less during the period from 1995 to 2004. The impact of land use and land cover on sediment discharge demonstrated characteristics of seasonal fluctuation. The effects of sediment reduction in the controlled watershed were greater than those in the uncontrolled watershed in May and September. In the controlled watershed, the reduction effect coincided with the distribution of rainfall. The amount of discharged flood sediments is closely correlated with rainfall, rainfall intensity in a 60 min period and the volume of flood. The rainstorm-runoff process and the rainstorm-sediment discharge process demonstrate that land cover has a strong regulatory and control function in the flood process and sediment discharge in rainstorms. For the controlled watershed, given the same precipitation frequency distribution, the average amount of sediment discharged during the land use period from 1995 to 2004 was less than that during the earlier land use period from 1986 to 1994 under every recurrent period. __________ Translated from Journal of Beijing Forestry University, 2007, 29(6): 115–122 [译自: 北京林业大学学报]     

Elastic-plastic Analysis of Timber Frame with FEM

Elastic-plastic analysis of timber frame and its seven strengthened projects are analyzed with the software ANSYS10.0. The numerical calculation and material mechanics calculation for the timber beam are compared to verify the correctness of the finite element model. The paper also analyzes the law of stress and strain of timber beam. In contrast with the yield load and ultimate load of strengthened timber frames, it shows that the lateral resistance of timber frame with corner supports is greatly improved. And a strengthened project for the timber frame is put forward.     

Plastic upper bound theory reliability analysis of coal gangue hills

We established the plasticity limit analysis reliability limit state equation and the reliability calculating formula for gangue hills using the JC method. This work was based on the plasticity mechanics limit analysis upper bound theory and traditional slice methods. A reliability index of gangue hill stability was derived using this equation. It was found that the safety coefficient of gangue hills derived by the limit state equation risks failure if the variability of cohesion and internal friction angle are not considered. When the variability of the strength parameters rises, the reliability theory more consistently projects practicality than the limit state equation for gangue hill stability assessment.     

桂林岩溶石山青冈栎种内与种间竞争的数量关系

根据野外调查数据,采用Hegyi单木竞争指数模型,定量地研究了桂林岩溶石山建群种青冈栎的种内、种间竞争关系.结果表明,青冈栎所受到的竞争强度随着林木径级的增大而逐渐减小,种内竞争明显较种间竞争剧烈.青冈栎种内和种间竞争强度的顺序为:青冈栎＞石山樟＞亮叶槭＞圆叶乌桕＞光叶海桐＞翅荚香槐＞梧桐＞黄连木＞铁屎米＞粗康柴.整个林分以及青冈栎种内对对象木的的竞争强度与对象木胸径之间的关系近似服从幂函数关系,而伴生树种对对象木的竞争强度与对象木胸径之间的关系近似服从对数函数关系,对象木胸径与竞争强度间呈显著负相关关系.     

黄土丘陵区农业生态安全评价指标体系初探

以纸坊沟流域为例，构建了黄土丘陵区流域农业生态安全评价指标体系。依据该流域近70a来的农业生态安全状况，将该流域生态经济系统演变过程划分为4个阶段。从这4个阶段入手分析影响农业生态安全的主要因子，得出了一系列评价指标。结合选取指标的科学性、动态性、实用性等基本原则，参考压力-状态-响应（PSR）模型和多位专家的建议，进一步筛选、分类和确定评价指标，从而建立了一套由生态环境、社会经济、综合功能3大类，20个具体指标构成的适宜于黄土丘陵区的农业生态安全评价指标体系。     

基于GIS的乌鲁木齐市城市荒山建设用地适宜性评价

为了评估荒山土地用作建设用地的适宜性程度,以乌鲁木齐市荒山为例,应用修正的多因子综合评价模型,采用Arc GIS 10.0的空间分析模块,综合考虑了坡度、坡向、交通等多项因子,并对不同因子赋予权重进行叠加,得到适宜性评价结果。结果显示:1前期资料收集的完整性对评价单元的划分和评价方法的选择影响很大。2地质和地貌条件对荒山建设用地适宜性评价具有重要影响。3不可用于建设用地的面积比重最大,占总面积的54.90%,不宜建设用地的比重占总面积的20.52%,可用于建设用地开发的面积,仅为4.39%,适宜建设用地占总面积的20.19%。评价结果可为乌鲁木齐市建设用地提供更多选择。     

丘陵岗地保护性耕作技术在江西省万安县果业生产中应用

介绍针对丘陵岗地开发中“水土流失加剧、土壤酸化趋重、土壤肥力下降明显”等问题而推广应用的保护性耕作技术和取得的成效.     

丘陵地区水稻收获机械的选型

丘陵地区的区域气候、水土和自然条件与平原地区不同,水稻的耕作制度和技术类型也有明显的区域特点.机械化收获是水稻生产机械化的一个重点,也是广大农民长期盼望解决的难题.收获机械的正确选型直接关系到水稻机械化收获技术的应用效果,因此必须根据丘陵地区的地理环境和气候条件的实际,合理选择水稻的收获方式和机具,确定收获机械的功率、喂入方式和行走装置类型等主要技术参数,结合当地农机部门引进推广、试用和示范的机具情况,选购成熟的产品和适合的机型与品牌.     

晋西黄土丘陵区飞播造林成效调查

对岚县、五寨在不同年度、不同立地条件下飞播造林的成效进行了调查，分析了飞播造林成效差的原因，以便为今后这一地区的生态环境建设提供科学依据。     

洱海东部面山石漠化土地生态恢复措施

对大理市洱海东部面山区域土地石漠化的原因进行分析,论述了石漠化土地的类型、分布及其面积.根据石漠化土地的具体情况和已进行过治理措施的效果,提出了以下治理措施和对策:进行森林植被的恢复(封山育林,人工造林);加强农田水利和农村能源建设;加强法治建设,严格进行现有植被的管理和保护;制定能激励当地民众参与治理的政策和措施.