Vegetation effects on sediment connectivity and processes in an ephemeral channel in SE Spain

High sediment delivery due to catchment and channel erosion can impact on waterway health and reservoir sedimentation. Methods that decrease sediment connectivity within the system are needed to address these potential impacts. Vegetation has the potential to decrease channel erosion and sediment transfers in dryland environments by increasing channel bed resistance and roughness. Detailed studies of vegetation and process interactions were undertaken within an ephemeral channel in SE Spain at three scales (channel network, reach and patch) by repeat surveys and mapping after floods. Connectivity mapping showed variations in vegetation type and density along the channel and that these influence sediment retention and channel erosion. Hydraulic calculations of vegetation roughness effects at 25 cross-sections down the channel indicate the influence of different vegetation type and characteristics. Particular attention was paid to the perennial grass Lygeum spartum because of its potential benefits in channel stabilisation. Sedimentation takes place within these reaches, mainly by trapping within and downstream of individual plants. Check dams have a profound influence on vegetation and sediment distribution in this channel but use of vegetated zones may be a more sustainable strategy of sediment control.     

http://www.sciencedirect.com/science/article/pii/S1674987111000211

Arid and semi-arid regions are susceptible to high levels of erosion.A rapid and cost effective methodological erosion assessment for these regions is required to describe and monitor the processes that control erosion.This study uses remote sensing to describe the contribution of several factors that control erosion.Topography,land use,vegetation density,soil properties and climatic proxies are used to determine erosion risk and to provide basic maps of water and soil conservation practices. A hierarchi...     

Flow dynamics and erosion rate of a representative karst basin (Upper Aniene River,Central Italy)

Experimental data refer to a preliminary estimate of suspended solid and solute load of a perennial river. The basin is composed almost entirely of bare mesozoic, highly fractured, karstified carbonate rocks of the central Apennine range. The suspended solid load related to stormflow events in 1991 corresponds to about 14,970 t yr^–1. For the same period the solute load is 60,060 t yr^–1 for a mean base flow discharge of 9.4 m³ s^–1. Based on the mean concentration of Ca + Mg in water, the value of dissolution of carbonate rocks of 37.1 m³ km^–2 (equivalent approximately to 0.04 mm yr^–1) was calculated. Physical and chemical variations that occur during storm events indicate the complex dynamic processes in the karst aquifer and the role undertaken by the epikarst as perched water reservoir and by the major conduits that develop through the vadose and saturated zones of the karst system.     

Deforestation modifying terrestrial organic transport in the Rio Tapajós, Brazilian Amazon

The concentration and biomarker compositions of sedimentary organic matter (OM) as well as fine and coarse suspended particles were analysed to identify the impact of deforestation on the transport of terrigenous organic matter (OM) in the Rio Tapajós, a major tributary to the Amazon. Substantial shifts in the concentration and composition of recently deposited sedimentary OM suggest that intensive deforestation over the last few decades has considerably modified the natural inputs of sedimentary materials to the aquatic ecosystems by disrupting the terrigenous fluxes of humus and soil materials from the drainage basin. The observed compositional changes of bulk OM and land derived biomarkers (e.g. lignin) in recent sediments illustrate a sedimentary enrichment in OM from soil horizons that, under normal forest cover, tend to be retained in the drainage basin. On average, the recently accumulated OM is nitrogen-rich ((C/N)a=12–15) and more highly degraded ((Ac/Al)v=0.4–0.6 and DHBA/V=0.15–0.20) than deep materials ((C/N)a=20–30, (Ac/Al)v=0.25–0.4, and DHBA/V=0.05–0.10), showing that this recently accumulated material is more humified than original inputs to the aquatic system, and consistent with increased exportation of fine eroded mineral and organic particles from surface soils along river banks. The present study illustrates the relevance of using OM oxidation products in sediment profiles to evaluate deforestation impacts on aquatic ecosystems and to characterize the nature of eroded soil materials, complementing studies on mineral/metal cycling.     

沿程淤积与溯源淤积的概念与数学模型

沿程淤积与溯源淤积是有关河床纵剖面调整的一对重要概念,但以前的一些文章对此的认识是互相矛盾的。本文对沿程淤积和溯源淤积的概念作了严格的限定,并给出了数量化的定义——沿程淤积与溯源淤积的数学模型。     

控制碰撞造山带热异常形成的主要因素及其地质作用分析

本文对剥蚀、逆冲断层剪切摩擦和放射性物质富集等因素对造山带热结构和热演化的影响进行了模拟计算以及定量分析,并对热异常与造山带内的若干地质现象之间的关系进行了讨论.在剪切生热模型的计算中考虑了逆冲断层的速度变化及其对热结构的影响,考察了断裂宽度与热结构之间的关系.计算中还考虑了两种热剪切计算模式,即:(1)瞬间推覆就位模式;(2)非瞬间推覆就位模式.从计算与讨论中得出如下认识:造山带后期的剥蚀使整个岩石层加热;剪切摩擦使壳内局部地区升温;放射性物质的富集主要使上部岩石层产生热异常.三者联合作用的结果使岩石层大幅度升温,从而形成造山带内部大范围的与其它地区不同的高温异常以及独特的地质特征.通过计算和讨论,文中认为:重熔型花岗岩和大量的构造岩是造山带内逆断层剪切作用的产物;与逆断层呈平行排列的拉张正断层是造山带在诸因素作用下升温,然后又经剥蚀,物质发生热收缩的结果.在造山带演化后期出现的这种拉张正断层代表造山带解体和向盆地转化的构造面貌.     

ON THE DYNAMIC MECHANISM OFEROSION PROCESS

Erosion process is controlled and affected by various forces of different nature. Erosion processes induced or affected by these forces can be classified into three cate- gories: erosion process induced by endogenic agent, by exogenic agent and associated with human activities. In this article, various dynamic mechanisms are systematically reviewed. Effects of tectonic stress and gravitational stress fields on erosion, effects of human activity on erosion, effect of exogenic forces such as water and wind erosion are discussed respectively.     

土壤坑蚀性实验研究

对采自内蒙东胜、河北张家口、山西离石和湖北通城、秭归等不同自然地理环境区的９２个土壤样，分别进行了其各项物理、化学特性的测定，和崩解、溅蚀、贯入试验，发现不同土类的试验结果与其理化性状之间存在规律性，它们是土壤抗蚀性的反映。文中还对不同土壤的抗蚀性大小进行了讨论。     

Discussion. Denudational isostatic rebound of intraplate highlands: The Lachlan river valley,Australia

Episodic terrace cutting cannot be a complex response to the steady isostatic rebound forecast by an elastic flexure model because three terraces match epiphreatic passage levels in nearby caves. There is also some doubt about how fluvial incision rates should be extrapolated to catchment-wide rates. At the local scale of the Lachlan River highlands, active tectonic compression may be more important than flexure, which is more important at a regional scale.     

苏北平原地下咸淡水形成与含水介质的关系

据第四纪沉积环境、海水进退过程,分析了地下咸淡水与含水介质的形成及关系。环境同位素表明,地下水与含水介质不属同生关系,而晚于含水介质形成,同生水已排泄入海。