青藏高原西部地表热通量输送的低频特征   总被引：1，自引：1，他引：0       下载免费PDF全文

张鹏飞  李国平  尹建昌 《高原气象》2009,28(3):556-563

以1997年9月-1998年10月青藏高原西部改则地区自动气象站(AWS)近地层连续观测的梯度资料为基础,计算了高原西部地面感热通量、蒸发潜热通量及地面热源强度,应用Marr小波变换重点分析了地表热通量输送以及与此相关的降水量、土壤湿度和土壤热通量的周期振荡特征.结果表明:地面感热具有明显的30～60天低频振荡,并且在夏季存在准8天的中期振荡;蒸发潜热和降水量以准双周振荡为主.土壤热通量以30～50天低频振荡为主,夏季还存在准8天的中期振荡;土壤湿度在冬季呈现明显的30～50天低频振荡,夏季则为20～30天的低频振荡.  相似文献   

Patterns and implications of plant-soil δC and δN values in African savanna ecosystems     

Lixin Wang  Paolo D'Odorico  Stephen A. Macko 《Quaternary Research》2010,73(1):77-3082

Southern African savannas are mixed plant communities where C₃ trees co-exist with C₄ grasses. Here foliar δ¹⁵N and δ¹³C were used as indicators of nitrogen uptake and of water use efficiency to investigate the effect of the rainfall regime on the use of nitrogen and water by herbaceous and woody plants in both dry and wet seasons. Foliar δ¹⁵N increased as aridity rose for both C₃ and C₄ plants for both seasons, although the magnitude of the increase was different for C₃ and C₄ plants and for two seasons. Soil δ¹⁵N also significantly increased with aridity. Foliar δ¹³C increased with aridity for C₃ plants in the wet season but not in the dry season, whereas in C₄ plants the relationship was more complex and non-linear. The consistently higher foliar δ¹⁵N for C₃ plants suggests that C₄ plants may be a superior competitor for nitrogen. The different foliar δ¹³C relationships with rainfall may indicate that the C₃ plants have an advantage when competing for water resources. The differences in water and nitrogen use likely collectively contribute to the tree-grass coexistence in savannas. Such differences facilitate interpretations of palaeo-vegetation composition variations and help predictions of vegetation composition changes under future climatic scenarios.  相似文献   

Local-scale spatial variability of soil organic carbon and its stock in the hilly area of the Loess Plateau, China   总被引：3，自引：0，他引：3  

Yafeng Wang  Yihe Lü  Yong Luan 《Quaternary Research》2010,73(1):70-76

Soil organic carbon (SOC) is one of the key components for assessing soil quality. Meanwhile, the changes in the stocks SOC may have large potential impact on global climate. It is increasingly important to estimate the SOC stock precisely and to investigate its variability. In this study, Yangjuangou watershed was selected to investigate the SOC distribution under different land uses. We found that SOC concentration decreased with increasing soil depth under all land uses and was significantly different across the vertical soil profile (P < 0.01). However, considering effect of land use on SOC, it is only significant (P < 0.01) in the topsoil (0-5 cm) layer. This indicated that land use has a large effect on the stocks of SOC in the surface soil. The stratification ratio of SOC > 1.2 may mean that soil quality is improving. The order of the SOC density (0-30 cm) under different land uses is forestland > orchard land > grassland > immature forestland > terraced cropland. The SOC stock is found to be as large as 2.67 × 10³ t (0-30 cm) in this watershed. Considering time effect of restoration, the slope cropland just abandoned is more efficient for SOC accumulation than trees planted in the semi-arid hilly loess area.  相似文献   

A critical political ecology of cotton and soil fertility in Mali     

Tor A. Benjaminsen  Jens B. Aune 《Geoforum》2010,41(4):647-656

The aim of this article is to analyse the influence of commodified cotton production on soil fertility in southern Mali. From the late 1950s and until recently, production of both cash-crop cotton and food crops have increased rapidly in this region, giving it a reputation of being an African ‘success story’. The flip side of this economic success is, however, said to be environmental degradation especially in terms of loss of soil fertility. We collected 273 soil samples in 19 villages located in various zones of land use intensity. In each village, the samples were collected on up to six different land use types varying with intensification. The analysis of the soil samples showed that soil fertility was highest in the sacred groves that have been protected and never cultivated. However, comparing soils under continuous cultivation and soils under fallow no clear trends in soil fertility were found. Cotton yields have declined since the early 1990s, while the total use of fertilisers has increased. This is often interpreted as proof of soil exhaustion, but there is no clear indication in this study that cotton-cereal rotation as practiced by smallholders in southern Mali reduces soil fertility. We argue that the decline in yields has been caused by an extensification process. Cotton fields expanded rapidly, due to attractive cotton prices in the 1990s, leading to falling investments per ha and cultivation of more marginal lands. These findings also have implications for a political ecology of commodity production and lead us to argue for an open-ended and empirically based ‘critical political ecology’.  相似文献   

景观格局与水土流失的尺度特征与耦合方法   总被引：11，自引：0，他引：11  

傅伯杰  徐延达  吕一河 《地球科学进展》2010,25(7):673-681

景观格局与生态过程的耦合研究是景观生态学研究的核心科学问题,也是综合自然地理学深化和发展的关键.尺度广泛存在于生态学现象中,尺度效应与尺度转换是景观生态学研究面临的挑战,探讨格局与过程之间相互作用机理与尺度特征是为解决尺度问题提供理论依据的必然途径.水土流失作为一种生态过程,是国内外颇为关注的生态问题.依据多种研究手段,在不同尺度上开展景观格局与水土流失的相互关系与尺度特征的研究,在分析景观格局的时空异质性、水土流失的影响因子与尺度效应的基础上,揭示流域景观格局与水土流失的耦合机理,发展尺度转换方法和景观格局-水土流失过程耦合模型,是完善景观生态学的理论基础,是为水土流失区生态建设提供科学依据的重要途径.  相似文献   

评估集合卡曼滤波反演土壤湿度廓线的性能     

苟浩锋  刘彦华  张述文  李得勤 《地球科学进展》2010,25(4):400-407

集合卡曼滤波由于易于使用而被广泛地应用到陆面数据同化研究中,它是建立在模型为线性、误差为正态分布的假设上,而实际土壤湿度方程是高度非线性的,并且当土壤过干或过湿时会发生样本偏斜.为了全面评估它在同化表层土壤湿度观测来反演土壤湿度廓线的性能,特引入不需要上述假设的采样重要性重采样粒子滤波,比较非线性和偏斜性对同化算法的影响.结果显示:不管是小样本还是大样本,集合卡曼滤波都能快速、准确地逼近样本均值,而粒子滤波只有在大样本时才能缓慢地趋近;此外,集合卡曼滤波的粒子边缘概率密度及其偏度和峰度与粒子滤波完全不同,前者粒子虽不完全满足正态分布,但始终为单峰状态,而后者粒子随同化推进经历了单峰到双峰再到单峰的变化.  相似文献   

云南省剑川县地质灾害调查及成因分析     

纪甲子  陈爱兵  李俊  姜海  董光泽 《云南地质》2010,29(4):471-474

详细分析剑川县境内地质灾害类型、空间分布特征及其成因,认为剑川县地质灾害以滑坡、泥石流为主。形成受地形地貌、地质构造、地层岩性、降雨、植被、人类工程活动等条件影响。  相似文献   

毛乌素沙漠风积砂力学特性室内试验研究     

宋焱勋  彭建兵  王治军  李喜安  赵兴考 《工程地质学报》2010,18(6):894-899

在对毛乌素沙漠风积砂物理特性进行试验研究的基础上,通过室内击试验、压缩试验及三轴剪切试验,对毛乌素沙漠风积砂的力学特性进行了初步研究。结果表明:毛乌素沙漠风积砂击实特性与粉、黏性土有较大的差异,在干燥和最佳含水率状态下易于击实,击实曲线呈双峰形态;压缩试验表明毛乌素沙漠风积砂一般属于低压缩性土,其压缩特性与试样初始密度、含水率、荷载级别及加载条件有关;三轴剪切试验表明毛乌素沙漠风积砂抗剪强度指标受试样密度的影响较大,虽然含水率对抗剪强度指标有一定影响且具有一定规律性,但影响程度并不明显。本文相关成果为解决该区风积砂相关岩土工程问题和工程地质问题提供了可靠的试验依据。  相似文献   

碳酸盐岩风化成土过程中的微生物作用   总被引：9，自引：0，他引：9  

连宾 《矿物岩石地球化学通报》2010,29(1):52-56

碳酸盐岩风化作用长期受到广泛关注,有关其成土的物源也一直是颇有争议的问题。基于前人有关碳酸盐岩风化成土作用的研究基础和对有关资料的调研与分析,结合各类研究成果,笔者提出了喀斯特地区岩石微生物的风化成土作用途径:微生物生长对矿物养料的吸收,以及分泌的代谢产物导致碳酸盐岩的破坏分解和一些次生矿物的形成;一些岩石微生物能够通过新陈代谢固定大气中的碳素和氮素,截留由雨水、风尘、大气气溶胶甚至空气流动所带来的土壤颗粒等外来物质。微生物在岩石表面与缝隙中的生长繁殖在碳酸盐岩风化成土这一漫长的地质演化过程中发挥了不可替代的重要作用。  相似文献   

基坑土钉墙支护施工工艺探究     

于宁 《城市地质》2010,5(4):45-48

土钉墙作为一种比较实用的原位岩土加固技术,近年来在深基坑支护工程中得到了广泛的应用。本文简要阐述了基坑土钉墙支护施工的主要步骤及相关技术,分析了深基坑土钉墙支护主要施工工艺。  相似文献