土壤侵蚀链内细沟浅沟切沟流动力机制研究

通过模拟降雨试验的方法,系统研究了细沟流流速与流量、水深与流量、流速与水深及阻力系数与雷诺数之间的关系,雨强与坡度对细沟流水力特性的影响,不同细沟流流型、流态及水动力要素作用下的侵蚀特点,并对浅沟与切沟流的水动力特性及侵蚀规律进行了初步探讨。研究结果对于揭示土壤侵蚀链内不同侵蚀方式下的水沙流动力学机制,以及土壤侵蚀演化规律具有重要意义。

土壤侵蚀链概念的科学意义及其特征

首次提出土壤侵蚀链的概念 ,简要分析了土壤侵蚀链概念的内涵与外延 ,以及土壤侵蚀链与通常所称的土壤侵蚀垂直分带的区别与联系。指出土壤侵蚀链具有等级层次性 ,动态演化过程的复杂性及类型多样性等 3个突出特征。从坡面水流的水动力参数变化特点 ,研究了侵蚀过程能量传递的特征。这些为研究和揭示坡沟系统土壤侵蚀链的动力机制 ,以及有效控制与治理黄土丘陵沟壑区的水土流失现象 。

黄土坡面细沟侵蚀的动力条件

黄土坡面各种侵蚀方式以水流能量、侵蚀物质及侵蚀微地貌３种作用方式相关联，水流能量是制约侵蚀物质和侵蚀微地貌时空分异的本质原因。研究表明，雷诺数（Ｒｅ）、弗罗德数（Ｆｒ）及过水断面单位能量（Ｅ）为判定不同侵蚀方式出现的水动力学指标。并运用实验方法确定出细沟侵蚀的动力临界为：Ｒｅ≥１４８６，Ｆｒ≥６．５１９，Ｅ≥１．３８７ｃｍ。

2008年汶川地震触发滑坡量大于造山作用生长量

浅源地震是山区地壳抬升的主要驱动力（Avouac，2008）。然而，浅源大地震也触发大范围的同震滑坡，造成显著、但在空间上不均匀的侵蚀（Keefer，1994；Malamud et al，2004；Larsen et al，2010）。因此地壳抬升与同震滑坡的分布及规模间的相互作用就引发了一个根本的问题，即大地震及其相关的滑坡是创生还是消毁了山区地形。2008年中国四川Mw7．9汶川地震触发了超过56000处滑坡（Dai et al，2011），其空间分布仅仅部分与构造变形样式有关（Shen et al，2009）。通过将滑坡面积一体积标度关系（Larsen et al，2010；Guzzetti et al，2009）应用于高分辨率卫星影像，我们仔细检查了造山方量的潜在变化。我们估计，同震滑坡产生了约5～15km^3的可侵蚀物质，大于2．6±1．2km^3（deMichele et al，2010）的同震地壳抬升净方量。这种差异表明，在可能的2000-4000年的地震复发周期中（Shen et al，2009），即使只有小部分滑坡物质从造山带中运移走，汶川地震也会在龙门山导致物质净亏损。我们的结果对长期以来广泛持有的大倾滑或走滑地震能造山的观点提出了挑战，并希望引起对同震滑移、滑坡量与地形生成之间的关系更多的思考研究。

A native herbaceous community exerts a strong allelopathic effect on the woody range-expander Betula fruticosa

Biological invasions by alien and range-expanding native plant species can suppress native plants through allelopathy.However,the homeland security hypothesis suggests that some native plants can resist invasion by producing allelopathic compounds that inhibit the growth of invasive plants.Most research has focused on allelopathic interactions between individual native and invasive plant species,with less emphasis on how allelopathy helps entire native communities resist invasions.Additionally,limited knowledge exists about allelopathic interactions between range-expanding native species and recipient native communities,and their influence on invasion success.To bridge this knowledge gap,we conducted two greenhouse competition experiments to test reciprocal allelopathic effects between a native woody range-expanding species,Betula fruticosa,and a community of four native herbaceous species(Sanguisorba officinalis,Gentiana manshurica,Sium suave and Deyeuxia angustifolia)in China.We assessed whether B.fruticosa and the native community differed in their competitive effects and responses,and whether these were influenced by activated carbon,which neutralizes allelochemicals in the soil.Activated carbon reduced the suppressive effects of the native community on the above-ground biomass of B.fruticosa,which indicates that the native community exerted a strong allelopathic effect on B.fruticosa.In contrast,activated carbon only marginally enhanced the suppressive effects of B.fruticosa on the native community,which indicates that allelopathy is not the primary mechanism by which B.fruticosa exerts its suppression.Overall,these findings support the homeland security hypothesis and suggest that biotic resistance from the native herbaceous community may limit the invasion success of the woody range-expander B.fruticosa.

Slope Processes, Mass Movement and Soil Erosion： A Review

Soil erosion and land degradation are global problems and pose major issues in many countries. Both soil erosion and mass movement are two forms of land degradation and humans play important roles in these geomorphological processes. This paper reviews slope processes associated with mass movement and soil erosion and contributory factors, including physical and human agents. Acting together, these cause diverse geomorphological features. Slope processes are illustrated by reference to case studies from Brazil and UK. The causes and impacts of erosion are discussed, along with appropriate remedial bioengineering methods and the potential of the measures to prevent these types of environmental degradation. Although there are several agents of erosion, water is the most important one. Cultivation can promote soil erosion, due to ploughing and harvesting, which moves soil down slopes. Soil erosion and mass movement data would inform the viability of soil conservation practices. Integrated management of drainage basins offers a Dromising way forward for effective soil conservation and soil remedial bioengineering in Brazil and UK.

Variability in the composition and export of silica in the Huanghe River Basin

Concentrations of suspended particle material(SPM), dissolved silicate(DSi), biogenic silica(BSi), phytoliths(plant produced siliceous microscopic structures), and other parameters were analyzed to examine the influence of both natural processes and human activities on silica delivery to the estuary of the Huanghe River(Yellow River). Our results indicate that the concentrations of DSi in the river decreased significantly since 1986. Approximately 34% of dissolved silica was trapped in the basin between 1986 and 2010 due to a reduction of soil erosion. Phytoliths comprised 67.2%–96.3% of BSi, with the smoothing bar type being the dominant form. Concentrations of BSi are significantly higher in the Huanghe River compared to other major rivers throughout the world due to its high sediment yield. We also found that the ratios of BSi/(BSi+DSi) and BSi/SPM were approximately 0.5 and 0.003 at Lijin near the river mouth, indicating that BSi carried in suspension by the Huanghe River was an important component of the rivers silica load. Significant amounts of BSi were also composed of phytoliths in Bohai Sea sediments near the Huanghe River estuary with the smoothing bar form again being the most abundant. The relatively high specific fluxes of BSi in the Huanghe River reflect its high turbidity and high erosion rates in the basin. The high sediment load originating on the Loess Plateau is likely responsible for the higher BSi flux, in agreement with a general trend of increasing BSi flux with increasing sediment flux in global river systems. This study demonstrates that BSi transported by rivers can be composed largely of phytoliths originating from the erosion of topsoils. The flux of phytoliths in river's suspended sediment load may therefore represent a significant contribution to the biogeochemical cycle of silica in coastal waters.