Towards quantifying the negative feedback regulation of peatland evaporation to drought          下载免费PDF全文

Nicholas Kettridge  J. M. Waddington 《水文研究》2014,28(11):3728-3740

The frequency and intensity of drought is projected to increase within the boreal region under future climatic conditions. Peatlands are widely considered to regulate water loss under drought conditions, increasing surface resistance (r_s) and reducing evaporative losses. This maintains peat moisture content, increasing the resilience of these globally important carbon stores. However, the magnitude and form of this important negative feedback response remains uncertain. To address this, we monitored the response of r_s to drought within four peat cores under controlled meteorological conditions. When the water‐table was dropped to a depth of 0.30 m and the humidity reduced to ≤40%, a step shift in r_s from ~50 s m^‐1 up to 1000 s m^‐1 was observed within burned and unburned peat, which virtually shuts down evaporation, limiting water loss. We show that measured near‐surface tension cannot be used to directly calculate this transition in peat surface resistance. However, empirical relationships that account for strong vertical variations in tension through the near‐surface and/or disequilibrium between pore air and near‐surface pore water pressure provide the potential to incorporate this negative feedback response into peatland ecohydrological models. Further observations are necessary to examine this response under dynamic atmospheric conditions. We suggest that the link between surface temperature and evaporation provides potential to further examine this feedback in either burned peatlands or peatlands with a low vascular vegetation cover. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Characterizing ephemeral streams in a southern Ontario watershed using electrical resistance sensors          下载免费PDF全文

Sarah E. Peirce  John B. Lindsay 《水文研究》2015,29(1):103-111

Ephemeral streams are small headwater streams that only experience streamflow in response to a precipitation event. Due to their highly complex and dynamic spatial and temporal nature, ephemeral streams have been difficult to monitor and are in general poorly understood. This research implemented an extensive network of electrical resistance sensors to monitor three ephemeral streams within the same small headwater catchment in Southern Ontario, Canada. The results suggest that the most common patterns of network expansion and contraction in the studied streams are incomplete coalescence and disintegration, respectively. Binary logistic regression analysis of the primary controls on ephemeral streamflow showed only weak Nagelkerke R² values, suggesting that there are more complex processes at work in these ephemeral streams. A comparison of all three streams suggests that even ephemeral streams within the same subwatershed may experience differences in network expansion and contraction and may be dominated by different spatial and temporal controls. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Conflicts over industrial tree plantations in the South: Who, how and why?     

Julien-Franois Gerber 《Global Environmental Change》2011,21(1):165-176

Industrial tree plantations for wood, palm oil and rubber production are among the fastest growing monocultures and are currently being promoted as carbon sinks and energy producers. Such plantations are causing a large number of conflicts between companies and local populations, mostly in the tropics and subtropics. Within a political ecology framework, the present paper investigates the nature of such conflicts as related to the alleged impacts of the plantations, the protesters involved, and the modalities of the conflicts with a special emphasis on their outcomes. Relying on the most comprehensive literature review to date, corresponding to 58 conflict cases, I find that the prominent cause of resistance is related to corporate control over land resulting in displacements and the end of local uses of ecosystems as they are replaced by monocultures. Resistance includes the “weapons of the weak” and ranges from dialogue to direct confrontation and from local to international. It often involves NGOs, especially for legal issues. Demonstrations, lawsuits, road blockades and tree uprooting have been reported in several countries. Authorities have responded by repression in about half of the cases analysed, while popular struggles have been able to stop plantations in about one fifth, mainly through winning lawsuits or massive social unrest. While these movements can be regarded as classical land conflicts, they usually also have an ecological content, corresponding to forms of the “environmentalism of the poor”. The documented large number of such conflicts suggests that policies promoting large-scale tree plantations should be reappraised.  相似文献   

国产珠状温度传感器对比分析     

李伟 《南京气象学院学报》2011,(4):346-353

通过比对试验,采取同球比对施放方式,选择德国GRAW探空仪作为比对标准,使用总共12次同球比对数据,对中国长峰、华云和大桥3种型号探空仪的珠状电阻温度传感器开展比对分析.经典型个例分析与统计分析表明:3个型号国产探空仪高空温度廓线与德国GRAW探空仪具有较好的整体一致性,温度测量夜间性能均好于白天;长峰探空仪温度探测性能随高度变化比较稳定,而华云探空仪与大桥探空仪性能相仿,均随高度性能下降,尤其是30km以上高空;长峰探空仪温度探测整体性能最好,相对系统误差在0.2℃左右;而华云探空仪与大桥探空仪误差可达1℃,且均表现为整体上温度测值偏低.体积较小的珠状温度传感器将是未来高空温度探测的一个好的选择,下一步需要改善华云探空仪与大桥探空仪温度传感器表面涂层工艺,两者的温度辐射订正算法也需要进一步完善.  相似文献   

无线铂电阻温度传感器测试系统     

唐慧强  鲍磊磊  李超 《南京气象学院学报》2011,(5):419-422

为实现对铂电阻温度传感器的自动测试,设计了基于ZigBee的铂电阻的测试系统.多个高精度微型铂电阻测试节点组网后把测试数据通过汇聚节点传输到计算机.在Windows的开发平台下,利用Delphi7.0+SQL Server2000技术进行软件研发,实现了铂电阻数据的自动采集、处理、传输、管理、性能评判等功能为一体的自动化测试系统,解决了传统测试系统需要大量布线的问题,提高了铂电阻温度传感器测试效率.  相似文献   

Characterisation of subsurface spatial variability using a cone resistivity penetrometer     

Hyung-Koo Yoon  Soon-Hyuck JungJong-Sub Lee 《Soil Dynamics and Earthquake Engineering》2011

The subsurface spatial variation in clay soils, such as thin-layered sand seams, affects the mechanical strength and electrical resistivity. The objective of this study is the development and application of cone resistivity penetrometer (CRP), which measures the cone tip resistance, sleeve friction, and electrical resistivity to evaluate the subsurface spatial variability. The electrical resistivity is measured at the cone tip to increase its resolution. Two outer diameters of the cone resistivity penetrometers (CRPs) are developed: D=10 mm CRP with a projected area of 0.78 cm² and D=15 mm CRP with a projected area of 1.76 cm². The cone tip resistance is effectively separated using a friction sleeve. Strain gauges are used to measure the mechanical strength, and coaxial type electrodes monitor the electrical resistivity. The application tests in the laboratory are conducted using layered soils and saturated sands. In addition, the penetration tests in the field are carried out and compared with the standard piezocone test. The penetration tests show that the soil layers and the density changes are clearly detected by the electrical resistivity and mechanical strength. Field tests show that CRP clearly evaluates the subsurface profile. This study suggests that CRP may be a useful technique for the evaluation of subsurface spatial variability during penetration testing.  相似文献   

Experimental investigation on seismic behavior of single piles in sandy soil     

Werasak Raongjant 《地震工程与工程振动(英文版)》2011,10(3)

This paper describes a quasi-static test program featuring lateral cyclic loading on single piles in sandy soil. The tests were conducted on 18 aluminum model piles with different cross sections and lateral load eccentricity ratios, e/d, (e is the lateral load eccentricity and d is the diameter of pile) of 0, 4 and 8, embedded in sand with a relative density of 30% and 70%. The experimental results include lateral load-displacement hysteresis loops, skeleton curves and energy dissipation curves. Lateral cap...  相似文献   

HPFL条带加固眠墙抗剪试验研究   总被引：4，自引：0，他引：4  

尚守平  姜巍 《震灾防御技术》2011,6(3):231-241

为了了解高性能水泥复合砂浆薄层(High Performance Ferrocement Laminate,简称HPFL)加固低强度眠墙的抗震性能,本文通过1片未加固眠墙和4片采用HPFL条带加固的眠墙的水平低周反复荷载试验,对比研究了各个墙片的抗震性能.试验结果表明,用HPFL条带加固后的眠墙显著提高了其开裂荷载和极...  相似文献   

Consolidation of vertical drain with depth-varying stress induced by multi-stage loading     

M.M. Lu  K.H. Xie  S.Y. Wang 《Computers and Geotechnics》2011

An explicit analytical solution is developed for the consolidation of vertical drain with both radial and vertical drainage by adopting a depth-varying stress induced by multi-stage loading. The well resistance and smear effect are also considered. The smear effect is described by three decay patterns of horizontal permeability towards drains within the smeared zone, including a reduced constant pattern, a linear decay pattern and a parabolic decay pattern. A parameter analysis is performed to investigate the consolidation behavior of the vertical drain. The convergence of the proposed series solution is discussed.  相似文献   

EH4法勘查祥云米甸煤矿隐伏塌陷区效果     

王鑫  钟云川 《云南地质》2011,30(1):75-77,88

运用EH4电磁测深法布置剖面,结合岩矿石电性参数及地质资料分析,对剖面实测数据进行反演,较准确地识别出隐伏塌陷区、煤矿采空区及松散浮土层等地质异常区域及范围,较好地确定可能的地质灾害。  相似文献