Late Quaternary vegetation changes around Lake Rutundu,Mount Kenya,East Africa: evidence from grass cuticles,pollen and stable carbon isotopes     

Dr M. J. Wooller  D. L. Swain  K. J. Ficken  A. D. Q. Agnew  F. A. Street-Perrott  G. Eglinton 《第四纪科学杂志》2003,18(1):3-15

Woody, subalpine shrubs and grasses currently surround Lake Rutundu, Mount Kenya. Multiple proxies, including carbon isotopes, pollen and grass cuticles, from a 755‐cm‐long core were used to reconstruct the vegetation over the past 38 300 calendar years. Stable carbon‐isotope ratios of total organic carbon and terrestrial biomarkers from the lake sediments imply that the proportion of terrestrial plants using the C₄ photosynthetic pathway was greater during the Late Pleistocene than in the Holocene. Pollen data show that grasses were a major constituent of the vegetation throughout the Late Pleistocene and Holocene. The proportion of grass pollen relative to the pollen from other plants was greatest at the last glacial maximum (LGM). Grass cuticles confirm evidence that C₄ grass taxa were present at the LGM and that the majority followed the cold‐tolerant NADP‐MEC₄ subpathway. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Numerical modeling for analyzing thermal surface anomalies induced by underground coal fires     

Stefan Wessling  Claudia Kuenzer  Winfried Kessels  Manfred W. Wuttke 《International Journal of Coal Geology》2008,74(3-4):175-184

Coal seams burning underneath the surface are recognized all over the world and have drawn increasing public attention in the past years. Frequently, such fires are analyzed by detecting anomalies like increased exhaust gas concentrations and soil temperatures at the surface. A proper analysis presumes the understanding of involved processes, which determine the spatial distribution and dynamic behavior of the anomalies.In this paper, we explain the relevance of mechanical and energy transport processes with respect to the occurrence of temperature anomalies at the surface. Two approaches are presented, aiming to obtain insight into the underground coal fire situation: In-situ temperature mapping and numerical simulation. In 2000 to 2005, annual temperature mapping in the Wuda (Inner Mongolia, PR China) coal fire area showed that most thermal anomalies on the surface are closely related to fractures, where hot exhaust gases from the coal fire are released. Those fractures develop due to rock mechanical failure after volume reduction in the seams. The measured signals at the surface are therefore strongly affected by mechanical processes.More insight into causes and effects of involved energy transport processes is obtained by numerical simulation of the dynamic behavior of coal fires. Simulations show the inter-relation between release and transport of thermal energy in and around underground coal fires. Our simulation results show a time delay between the coal fire propagation and the observed appearance of the surface temperature signal. Additionally, the overall energy flux away from the burning coal seam into the surrounding bedrock is about 30-times higher than the flux through the surface. This is of particular importance for an estimation of the energy released based on surface temperature measurements. Finally, the simulation results also prove that a fire propagation rate estimated from the interpretation of surface anomalies can differ from the actual rate in the seam.  相似文献   

内蒙古桌子山煤田火区特征及灭火方法探讨     

田晓华 《中国煤炭地质》2008,(11):12-14

内蒙古自治区桌子山煤田赋存着较为稀缺的煤种一焦煤,煤田内存在的火区不仪烧掉了宝贵的焦性煤炭资源,给煤矿生产带来严重的事故隐患,对当地生态环境也造成极大的破坏。经查明区内有26处子火区,分布面积约760万m^2,通过煤田地质特征、煤质特征、地表指示特征、同位素氡气的浓度相对分布特征、物性特征分析了区内煤层发火原因,根据桌子山煤田火区特点,建议采用浅剥、深灌与覆盖相结合的灭火方法,并对火区进行动态监测。  相似文献   

Biomass burning in the tropical savannas of Ivory Coast: An overview of the field experiment Fire of Savannas (FOS/DECAFE 91)   总被引：1，自引：0，他引：1  

J. P. Lacaux  J. M. Brustet  R. Delmas  J. C. Menaut  L. Abbadie  B. Bonsang  H. Cachier  J. Baudet  M. O. Andreae  G. Helas 《Journal of Atmospheric Chemistry》1995,22(1-2):195-216

FOS/DECAFE 91 (Fire of Savannas/Dynamique et Chimie Atmosphérique en Forêt Equatoriale) was the first multidisciplinary experiment organized in Africa to determine gas and aerosol emissions by prescribed savanna fires. The humid savanna of Lamto in Ivory Coast was chosen for its ecological characteristics representative of savannas with a high biomass density (900 g m^–2 dry matter). Moreover the vegetation and the climate of Lamto have been studied for more than twenty years. The emission ratios (X/CO₂) of the carbon compounds (CO₂, CO, NMHC, CH₄, PAH, organic acids and aerosols), nitrogen compounds (NO_x, N₂O, NH₃ and soluble aerosols) and sulfur compounds (SO₂, COS and aerosols) were experimentally determined by ground and aircraft measurements. To perform this experiment, 4 small plots (100×100 m) and 2 large areas (10×10 km) were prepared and burnt in January 1991 during the period of maximum occurrence of fires in this type of savanna. The detailed ecological study shows that the carbon content of the vegetation is constant within 1% (42 g C for 100 g of vegetal dry matter), the nitrogen content (0.29 g N for 100 g of dry matter) may vary by 10% and the sulfur content (0.05 g S/100 d.m.) by 20%. These variations of the biomass chemical content do not constitute an important factor in the variation of the gas and particle emission levels. With the emission ratios characteristic of humid savanna and flaming conditions (CO/CO₂ of 6.1% at the ground and 8% for airborne measurements), we propose a set of new emission factors, taking into account the burning efficiency which is about 80%: 74.4% of the carbon content of the savanna biomass is released to the atmosphere in the form of CO₂, 4.6% as CO, 0.2% as CH₄, 0.5% as NMHC and 0.7% as aerosols. 17.2% of the nitrogen content of the biomass is released as NO_x, 3.5% as N₂O, 0.6% as NH₃ and 0.5% as soluble aerosols.  相似文献   

Occurrence of microorganic pollutants in the atmosphere of Singapore during haze and non-haze periods     

Rajasekhar Balasubramanian Chanbasha Basheer Kang Lisa Siao Wei See 《中国地球化学学报》2006,25(B08):183-183

Microorganic pollutants such as polycylic aromatic hydrocarbons （PAHs）, organochlorine pesticides （OCPs）, polychlorinated biphenyls （PCBs） and total petroleum hydrocarbons （TPHs） are known to be present in urban ambient air. These organic compounds are prone to atmospheric transport and deposition over long distances, thus enabling them to accumulate even in regions remote from their sources. Deposition from the atmosphere can be via direct deposition and exchange with crops that may be directly or indirectly ingested by humans. It can also take place via wet and dry deposition and air-water exchange. Following their deposition, these microorganic pollutants tend to accumulate in soils, sediments and in human and ecological food chains. There are many reports in the literature on the atmospheric concentrations of microorganic pollutants, but there are few reports and data in Asia. This study was performed in Singapore to determine the relative amounts of persistent organic pollutants and TPHs in ambient aerosols. One of the important sources of these organic compounds in Southeast Asia is thought to be biomass burning （vegetation fires）. Hence, air sampling was conducted during both smoke haze and non-haze periods. The data obtained from this study will be presented and discussed.  相似文献   

Integrated Approaches,Multiple Scales: Snag Dynamics in Burned Versus Unburned Landscapes*     

Joy Nystrom Mast  Carol L. Chambers 《The Professional geographer》2006,58(4):397-405

By studying landscape form and patterns, we can study processes at multiple scales and determine how collectively those processes inform us about function(s). Integrating landscape ecology from a biogeographical perspective with geographic information science (GIScience) practices offers new ways to study how landscapes change over time and space, including how they can be measured, analyzed, and modeled for management needs. This article presents methodologies and selected results of analyzing spatial patterns from field data across multiple scales by examining standing dead tree (snag) processes across wildfire‐disturbed landscapes in Arizona. Our primary motivation was to illustrate a particular type of work benefiting from the coalescing of landscape ecology and GIScience, functioning at the methodological and practical overlap of these two contributing fields. Our management goals were to (1) describe spatial patterns and characteristics of snags in pairs of burned and unburned ponderosa pine forests of Arizona in four recent (within the past ten years) wildfires, (2) document bird response to wildfires by combining landscape ecology and GIScience methods, and (3) link these patterns to snag monitoring plots and cavity‐nesting bird use to predict the probability of snag use by birds and cavity nesters based on snag characteristics (snag use model). The methods and results demonstrate how integration of landscape ecology with both GIS and GIScience improves the ways to study landscapes and land management issues, in this case offering guidelines for retention of snags that provide habitat for wildlife.  相似文献   

多源遥感技术在汝箕沟煤田火区动态监测中的应用   总被引：3，自引：0，他引：3  

王晓鹏万余庆  张光超林燕  张忠富王军 曹主军 《中国煤田地质》2005,17(5):28-31

以高空间分辨率的Quickbird卫星图像和高光谱分辨率的OMIS Ⅰ航空高光谱图像数据为信息源,结合细分光谱仪、红外测温计等地面遥感技术,对宁夏汝箕沟煤田的煤火现状进行了定量调查分析及动态监测,查明了煤田煤火的范围、强度,分析了不同时期煤田火区的变化规律,评价了火区治理效果并对后续灭火工作提出建议,为火区治理提供了决策依据.  相似文献   

山西运城市森林火险等级预报系统   总被引：1，自引：0，他引：1  

陈雪珍 《山西气象》2002,(1):14-16

利用有关气象及森林火灾资料，分析了林林火灾的发生与气象条件、火条件及森林含水率的关系，计算了森林火险综合预报指标，建立了以预报方程，经试用效果良好。  相似文献   

古炭屑与古森林火?   总被引：9，自引：1，他引：9       下载免费PDF全文

吕静  王宇飞  李承森 《古地理学报》2002,4(2):71-76

森林火普遍发生在地质历史时期中，它对自然植被系统的演替起着重要作用。不同强度和频率的森林火培育出不同类型的植被：频繁的森林火导致草甸的形成，而热带雨林形成的原因之一是森林火的缺乏。古炭屑作为古森林火的遗迹，具有分布广泛、细胞结构保存完好以及原地埋藏等特点，为研究古森林火发生的强度和频率提供了宝贵的材料。古炭屑的出现与当时的气候因素、植被类型和地理状况有密切关系：干旱、少雨的气候常常伴随高频率森林火的发生，表现出古炭屑的数量增多；易燃物种组成的植被易发生森林火，古炭屑的出现也会增多，而耐火树种会降低森林火的强度，古炭屑则出现少。因此，从古炭屑的数量和种类的变化，可探讨古森林火的发生规律，进而推断长期地质历史时期的气候、植被、地理状况的演变。  相似文献   

ISO-834标准火灾作用后钢管混凝土的轴压刚度和抗弯刚度   总被引：4，自引：1，他引：4  

霍静思  韩林海 《地震工程与工程振动》2002,22(5):143-151

火灾后钢管混凝土的轴压刚度和抗弯刚度是钢管混凝土结构变形性能和抗震分析的重要指标，也是火灾后钢管混凝土修复和加固的重要依据之一，本文利用数值方法计算了标准火灾作用后钢管混凝土轴压构件和纯弯构件荷载-变形关系曲线，分析了受火时间、材料强度、含钢率、截面尺寸等因素的影响规律，最后推导了标准火灾作用后钢管混凝土轴压刚度和抗弯刚度的简化计算公式，所得结果可供有关钢管混凝土结构工程设计时参考。  相似文献