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51.
There is a consensus that sediment delivery ratio in the Chinese Loess Plateau is close to 1 at the inter-annual timescale. However, little information is available about the sediment delivery at finer timescales. We evaluated the sediment delivery from plots to watersheds at the event or intra-annual, annual, and inter-annual timescales within the Wudinghe river basin, a 30, 261 km2 basin in the Loess Plateau. We calculated the ratio of sediment output to sediment input and presented the temporal change of the channel morphology to determine whether sediment deposition occurs. Although a single flood event frequently has a sediment yield exceeding 10, 000 t km−2, sediment deposition rarely occurs except during some small runoff events (sediment yield < 5000 t km −2) or dry years (sediment yield < 10, 000 t km −2) when moving from slopes up to the main channels of the Wudinghe River. This observation suggests a sediment delivery ratio close to 1 even at the event or intra-annual and the annual timescales, but not necessarily at the interannual timescale. Such a high sediment delivery ratio can be related to hyper-concentrated flows, which have very strong sediment transport capacity even at low flow strength. Because hyper-concentrated flows are well-developed in the whole Loess Plateau, a sediment delivery ratio close to 1 below the interannual timescale possibly remains true for other rivers in the Loess Plateau. 相似文献
52.
Extreme freeze-thaw action occurs on the Qinghai-Tibet Plateau due to its unique climate resulting from high elevation and cold temperature. This action causes damage to the surface soil structure, as soil erosion in the Qinghai-Tibet Plateau is dominated by freeze-thaw erosion. In this research, freezing–thawing process of the soil samples collected from the Qinghai–Tibet Plateau was carried out by laboratory experiments to determinate the volume variation of soil as well as physical and mechanical properties, such as porosity, granularity and uniaxial compressive strength, after the soil experiences various freeze–thaw cycles. Results show that cohesion and uniaxial compressive strength decreased as the volume and porosity of the soil increased after experiencing various freeze–thaw cycles, especially in the first six freeze–thaw cycles. Consequently, the physical and mechanical properties of the soil were altered. However, granularity and internal friction angle did not vary significantly with an increase in the freeze–thaw cycle. The structural damage among soil particles due to frozen water expansion was the major cause of changes in soil mechanical behavior in the Qinghai–Tibet Plateau. 相似文献
53.
SHANG Wen ZHAO Lin WU Xiao-dong LI Yu-qiang YUE Guang-yang ZHAO Yong-hua QIAO Yong-ping 《山地科学学报》2015,15(4):1010-1024
As a key attribute of soil quality, soil organic matter (SOM) and its different fractions play an important role in regulating soil nutrient cycling and soil properties. This study evaluated the soil carbon (C) and nitrogen (N) concentrations in different SOM fractions (light– and heavy fractions, microbial biomass) under different vegetation types and analyzed their influencing factors in continuous permafrost regions along the Qinghai-Tibet Highway in the North of Kunlun Mountains, China. Soil samples were collected in pits under four vegetation types — Alpine swamp meadow (ASM), Alpine meadow (AM), Alpine steppe (AS) and Alpine desert (AD) — at the depth of 0-50 cm. The vegetation coverage was the highest at ASM and AM, followed by AS and AD. The results indicated that the concentrations of light fraction carbon (LFC) and nitrogen (LFN), and microbial biomass carbon (MBC) and nitrogen (MBN) decreased as follows: ASM > AM > AS > AD, with the relatively stronger decrease of LFC, whereas the heavy fraction carbon (HFC) and nitrogen (HFN) concentrations were lower in AS soils than in the AD soils. The relatively higher proportions of LFC/SOC and MBC/SOC in the 0-10 cm depth under the ASM soils are mainly resulted from its higher substrate input and soil moisture content. Correlation analysis demonstrated that aboveground biomass, soil moisture content, soil organic carbon (SOC) and total nitrogen (TN) positively correlated to LFC, LFN, HFC, HFN, MBC and MBN, while pH negatively correlated to LFC, LFN, HFC, HFN, MBC and MBN. There was no relationship between active layer thickness and SOM fractions, except for the LFC. Results suggested that vegetation cover, soil moisture content, and SOC and TN concentrations were significantly correlated with the amount and availability of SOM fractions, while permafrost had less impact on SOM fractions in permafrost regions of the central Qinghai–Tibet Plateau. 相似文献
54.
LI Lei XIA Yin-hang LIU Shu-juan ZHANG Wei CHEN Xiang-bi ZHENG Hua QIU Hu-sen HE Xun-yang SU Yi-rong 《山地科学学报》2015,157(5):1229-1240
The conventional method which assumes the soil distribution is continuous was unsuitable for estimating soil organic carbon density (SOCD) in Karst areas because of its discontinuous soil distribution. The accurate estimation of SOCD in Karst areas is essential for carbon sequestration assessment in China. In this study, a modified method, which considers the vertical proportion of soil area in the profile when calculating the SOCD, was developed to estimate the SOCD in a typical Karst peak-cluster depression area in southwest China. In the modified method, ground-penetrating radar (GPR) technology was used to detect the distribution and thickness of soil. The accuracy of the method was confirmed through comparison with the data obtained using a validation method, in which the soil thickness was measured by excavation. In comparison with the conventional method and average-soil-depth method, the SOCD estimated using the GPR method showed the minimum relative error with respect to that obtained using the validation method. At a regional scale, the average SOCDs at depths of 0–20 cm and 0–100 cm, which were interpolated by ordinary kriging, were 1.49 (ranging from 0.03–5.65) and 2.26 (0.09–11.60) kgm−2based on GPR method in our study area (covering 393.6 hm2), respectively. Therefore, the modified method can be applied on the accurate estimation of SOCD in discontinuous soil areas such as Karst regions. 相似文献
55.
Accessibility to organic carbon (OC) budget is required for sustainable agricultural development and ecosystem preservation and restoration. Using geostatistical models to describe and demonstrate the spatial variability of soil organic carbon (SOC) will lead to a greater understanding of this dynamics. The aim of this paper is to present the relationships between the spatial variability of SOC and the topographic features by using geostatistical methods on a loess mountain-slope in Toshan region, Golestan Province, northern Iran. Hence, 234 soil samples were collected in a regular grid that covered different parts of the slope. The results showed that such factors as silt, clay, saturated moisture content, mean weighted diameter (MWD) and bulk density were all correlated to the OC content in different slope positions, and the spatial variability of SOC more to slope positions and elevations. The coefficient of variation (CV) indicated that the variability of SOC was moderate in different slope positions and for the mountain-slope as a whole. However, the higher variability of SOC (CV = 45.6%) was shown in the back-slope positions. Also, the ordinary cokriging method for clay as covariant gave better results in evaluating SOC for the whole slope with the RMSE value 0.2552 in comparison with the kriging and the inverse distance weighted (IDW) methods. The interpolation map of OC for the slope under investigation showed lowering SOC concentrations versus increasing elevation and slope gradient. The spatial correlation ratio was different between various slope positions and related to the topographic texture. 相似文献
56.
Unsaturated shallow soil deposits may be affected by either superficial soil erosion or shallow landslides in adjacent or overlapping source areas and in different seasons when a different soil suction exists. The triggering analysis of both these processes is a relevant issue for the hazard analysis while the literature mostly provides specific approaches for erosion or for landslides. The paper proposes a large-area analysis for a case study of Southern Italy, consisting of unsaturated shallow deposits of loose pyroclastic (air-fall) volcanic soils that have been repeatedly affected by erosion and landslides in special seasons. For a past catastrophic event, the simulated source areas of shallow landslides are smaller than those observed in the field while the simulated eroded areas with thickness greater than 5 cm are comparable with the in-situ evidences, if the analysis takes into account high rainfall intensity and a spatially variable soil cover use. More in general, the results of the paper are consistent with the previous literature and also provide a methodological contribution about the application of distinct tools over large area. The added value is that the paper shows how the combination of distinct large-area analyses may help with understanding the dominant slope instability mechanisms. Only once this goal is fully achieved, can specific physically-based analyses be confidently performed at detailed scales and for smaller specific areas. 相似文献
57.
利用回流法合成隧道结构的锰钾矿,并研究其光化学降解苯酚的效果及影响因素。分别采用X射线衍射、原子吸收光谱、扫描电镜、透射电镜和BET氮气吸附法对锰钾矿的晶体结构(包括晶型、晶胞参数和结晶度)、化学组成、微观形貌和比表面积进行了表征。研究表明,非光照时锰钾矿对苯酚的降解效果较差,光照能显著促进锰钾矿对苯酚的降解;光照条件下,p H值减小能显著促进锰钾矿对苯酚的降解;锰钾矿用量增加至1.00 g/L时能显著促进锰钾矿降解苯酚,但继续增加矿物用量却显著降低苯酚降解率;非光照条件下,p H值减小和矿物用量增加不能显著促进锰钾矿降解苯酚。 相似文献
58.
本文基于沿河土家族自治县耕地质量地球化学调查评价项目野外调查数据资料,分析了耕地土壤元素在不同成土母岩及不同土壤类型的地球化学特征。在摸清耕地土壤地球化学特征的基础上,利用SPSS统计分析软件,对全县表层土壤样品22个元素(指标)进行因子分析,得到有代表性的7个因子成分,分析不同元素组合的区域分布基于何种因素,并对各主因子进行了地质解释:F1主因子代表的变量与地质背景密切相关;F2主因子代表的变量与土壤中的As、Mo、Se与有机质易形成络合物有关;F3主因子代表的变量与区域上常形成与矿产有关的地球化学异常有关;F4主因子代表的变量可能与人工施肥及植被有关;F5主因子代表的变量与铜矿床有关;F6主因子代表的变量与分布的地层岩性有关;F7主因子代表的变量与萤石矿有关。根据全县富硒、富锗特色耕地分布特征及农产品优势,建议优先开发塘坝镇、新景镇等4个区域,为沿河县调整农业种植结构、发展现代山地特色优质农产品提供地球化学依据。 相似文献
59.
旁压试验在苏通大桥地质勘察工程中的应用 总被引：6，自引：2，他引：6
详细介绍了旁压试验的使用方法,以及受潮汐影响的大桥勘察旁压原位测试中的特殊处理措施,分析了旁压试验中各强度参数指标的处理方法和原则,并运用这些方法和原则处理了苏通大桥旁压试验的强度参数指标,为大桥的设计提供了设计强度参数,也可为同类工程提供参考意义。 相似文献
60.
黄土边坡的变形破坏一般与地表水入渗导致的地下水位上升有关。然而,现场观测发现黄土地区地表水入渗深度有限,降雨的湿润峰一般在2m以内。自湿润峰以下至地下水位之间很长一段的含水率是不变的,那么地表水是如何补给地下水的,一直存在争议。为此,本文利用甘肃正宁县地区的Q3黄土重塑样进行非饱和渗透特性的土柱试验。在一个4m高的玻璃桶内制备土样,土柱上按一定间距插入水分计探头,在顶部按每天1000mL水量均匀渗入水,测得给定时间沿土柱的含水率剖面。结果发现,随着补给时间的延长,湿润峰下移,湿润峰经过的上半土柱含水率几乎不变,当湿润峰到达土柱底部时,形成潜水位,这和现场观察的现象一致。这说明在地表活动带以下,饱和带以上,虽然土的含水率不变,但存在着稳定非饱和渗流,这是黄土地区地下水的唯一补给方式。 相似文献