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101.
Soil (SL) and organic carbon losses (SOCL) have increased with human population and climate change linked extreme events. While SL and SOCL are clearly associated with surface run‐off, the impact of land use is still not well understood. This article elucidates the effects of land use, surface cover, and other environmental factors on SL and SOCL using data from 55 published studies. The overall SL (12.34 ± 2.25 Mg ha?1 year?1) and SOCL (21.80 ± 0.91 g C m?2 year?1) suggests substantial losses of the fertile topsoil globally. Grasslands (4.19 ± 1.22 Mg ha?1 year?1) had 77%, 66%, and 41% lower SL than orchards, croplands, and forests, respectively, which is attributable to higher soil organic matter and surface cover. Croplands had the highest SOCL at 22.78 ± 2.22 g C m?2 year?1. Natural vegetation had 98% and 70% lower run‐off and SL than did plant residue mulched plots, indicating its great potential for surface run‐off and soil erosion control. Rainfall and slope were key drivers of soil erosion, while soil surface cover, SOC, and clay content decreased. These findings improve our knowledge on soil and organic carbon losses, which is useful for fostering sustainable management of soils and natural vegetation to enhance ecosystems functionality. 相似文献
102.
Examining four colonial soil conservation schemes in East Africa that were part of the modernising project of colonialism, this article considers multiple historical geographies of the colonised world. There were multiple modernities: while information and ideas flowed in many directions between (and within) the metropole and colonies, the particular ‘modernity’ that was put into practice was shaped by its context. The article highlights therefore that – despite playing to the same tune of modernity – colonialism was highly differentiated in the way that its policies played out on the ground. Furthermore, the ‘colonised’ acted and reacted to the policies in highly differentiated ways that depended on their particular context in time and space. All but one of the soil conservation schemes examined were rejected and there was significant resistance to them. Much of the existing literature on such schemes examines them in the context of essentially political processes, and in particular their influence on rising nationalism. Whilst these processes are important, this paper shows that there were other, non-political, factors that influenced the reception they were given, which need to be considered too. These ‘everyday’ details were about the practical and technical nature of the schemes, and by exploring these aspects of the schemes, and comparing them, the article highlights why most were rejected. It suggests that different aspects of conservation schemes need to be explored for a firm understanding of the reasons behind resistance to such schemes. 相似文献
103.
A selection of plant species that may have been relevant for the Neolithic in the SW Mediterranean have been characterised with pyrolysis gas chromatography mass spectrometry (pyrolysis–GC/MS) in search for molecular vegetation markers. Roots and aerial parts were analysed separately for the following species: Anthyllis cytisoides, Asphodelus cerasiferus, Brachypodium retusum, Cistus albidus, Cistus clusii, Dorycnium pentaphyllum, Ephedra fragilis, Juniperus oxycedrus, Juniperus phoenicea, Olea europaea, Phillyrea angustifolia, Pinus halepensis, Pistacia lentiscus, Quercus coccifera, Rhamnus lycioides, Rosmarinus officinalis, Smilax aspera and Stipa tenacissima; furthermore domesticated plants were analysed, including wheat (Triticum aestivum, Triticum dicoccum, Triticum monococcum, Triticum timopheevi and Triticum turgidum), barley (Hordeum vulgare and H. vulgare Hulled) and legumes (Lathyrus cicera, Lathyrus sativus, Lens culinaris, Pisum sativa, Vicia ervilia, Vicia faba and Vicia sativa). This resulted in 290 potential markers. In addition, the organic matter of surface soils under different vegetation cover has been analysed to test the presence of the potential markers in the soil. Forty-six of the potential markers were detected in the soil organic matter, of which part have not been reported before. The results may be useful for interpretation of the organic matter composition of soils and plant remains, which can be valuable in archaeology. 相似文献
104.
105.
根据历史文献和考古调查,确定出甘肃省庆阳市西峰区彭原乡的两座古城遗址分别是后汉富平县城(GC1)和唐宋彭原县城(GC2),唐宋彭原县是北魏永和元年(434年)以后从今庙头嘴村搬迁到南庄村。据此推断泾河四级支流、马莲河三级支流彭原沟(当地称湫沟)流域的现代侵蚀沟,是在此年以后开始发育的。利用黄土高原现代侵蚀沟地貌年龄计算公式,计算出彭原沟主干沟道现代侵蚀沟的地貌年龄为1669±819年,沟口附近的现代侵蚀沟发育于西晋成帝咸康五年(339年)前后,其主要分支沟谷现代侵蚀沟的地貌年龄介于900±442~1300±638年之间。沟头平均延伸速度为3.367m/a,沟谷平均下切速度为0.063m/a,平均加宽速度0.19m/a。公式计算结果与考古结果基本相符,研究结果具有较高的信度。依此结果,将彭原沟及其支流地貌复原至西晋时期。 相似文献
106.
Sumanta Haldar 《Journal of Earthquake Engineering》2013,17(6):737-757
The behavior of pile foundations in non liquefiable soil under seismic loading is considerably influenced by the variability in the soil and seismic design parameters. Hence, probabilistic models for the assessment of seismic pile design are necessary. Deformation of pile foundation in non liquefiable soil is dominated by inertial force from superstructure. The present study considers a pseudo-static approach based on code specified design response spectra. The response of the pile is determined by equivalent cantilever approach. The soil medium is modeled as a one-dimensional random field along the depth. The variability associated with undrained shear strength, design response spectrum ordinate, and superstructure mass is taken into consideration. Monte Carlo simulation technique is adopted to determine the probability of failure and reliability indices based on pile failure modes, namely exceedance of lateral displacement limit and moment capacity. A reliability-based design approach for the free head pile under seismic force is suggested that enables a rational choice of pile design parameters. 相似文献
107.
Recent developments in digital technologies are heralding significant changes in the way we acquire, visualise and analyse archaeological data. Terrestrial laser scanners can be used to create photo-realistic virtual copies of landscapes, and archaeological features, and offer the potential to improve our understanding of three-dimensional (3D) spatial relationships at study sites. Here we present a methodology for the integration of a high-resolution 3D site model with soil chemical data obtained from an abandoned settlement site located in the Central Highlands of Scotland. At this site, the multi-element concentration in soil, co-visualised within a topographic setting, has an important role to play in elucidating settlement layout and activity. The methods described here are also of significance in archiving sites of archaeological/historical importance where development activities and/or environmental processes may destroy remains, or where access to field sites is restricted. 相似文献
108.
An approach to mitigate the seismic risk of existing structures by means of the creation of a continuous thin layer of grouted soil at a convenient depth is presented. A parametric numerical analysis is reported using different constitutive models with reference to two geometrical schemes. It is shown that if the grouted layer has a stiffness significantly lower than that of the surrounding soil, it may be effective in reducing the seismic demand. In the parametric analyses, the positive role of yielding is also observed, which indicates that the barrier is more effective with larger input amplitudes. 相似文献
109.
通过对谭家坡遗迹馆微环境长期监测,遗迹馆内的空气温度、相对湿度、土壤温度以及土壤含水率监测数据进行对比分析,对修建外围保护建筑下的遗址环境有了初步的了解,并从监测结果中得出遗迹馆内空气温度、相对湿度、土壤温度与含水率的变化规律与特征。研究结果表明,潮湿多雨的气象环境造成谭家坡遗迹馆内高温、高湿,遗址土体也容易遭受地下水的侵蚀,对遗址直接或间接引发病变,或加速物理和生物的破坏作用。建议科学而恰当在控制遗址保存环境,建立环境数据库,形成一套完整的预测、预警监控体系。 相似文献
110.
室外土遗址经常因遭遇降雨、水淹等发生结皮,造成土遗址表层性能改变,影响土遗址的进一步保护。以定量纯净黄土在等降雨大小下,通过控制不同降雨时长,试验了不同降雨时长下土壤结皮发育的过程,分别测试了降雨前后的结皮厚度、密度、硬度及孔隙结构。结果表明,在降雨量未达到饱和状态时,随降雨量增大,结皮层的厚度、密度、硬度迅速增大,表皮土壤颗粒被击碎,孔隙迅速减小;在降雨量达到饱和状态时,随降雨量增大,结皮层的厚度、密度、硬度缓慢增大,但表皮土壤裂缝迅速发育,由周围向中心形成同心圆状或辐射状裂隙。研究结论可为室外土遗址的保护提供参考。 相似文献