Problems of the solution: intervention into small-scale irrigation for drought proofing in the Mekele Plateau of northern Ethiopia     

Yohannes Aberra 《The Geographical journal》2004,170(3):226-237

The Mekele Plateau, located in the semi-arid northern highland region of Ethiopia, is a drought-prone, highly degraded area. It has long been neglected by policymakers and thus recurring famine, widespread poverty, armed conflicts and mass outmigration have contributed to the near collapse of the farming systems and the livelihoods of the population. Traditional stream diversion irrigation has been practised in this area for several centuries. The systems of water management in particular may be considered inappropriate owing to the need for thriftiness in water use imposed by the local environment. The systems of headworks and canals are crude and wasteful on water. Recent interventions to improve the small-scale irrigation systems of the area have not been successful. Most interventions have preferred to introduce rainwater harvesting systems using micro-dams rather than trying to upgrade the traditional diversion schemes. Evaluation of irrigation structures in the field, interviews with key informants in government, analysis of documents and discussions with irrigators indicate that both the Ministry of Agriculture and SAERT-Commission's rainwater harvesting programmes have generally failed. The case of the most recent intervention by SAERT has failed because of myopic project planning, inadequate engineering studies, unsound designs, too short a time for implementation, and lack of full farmer involvement at different levels of project planning and implementation.  相似文献   

Economic analysis for the production of four grape cultivars using microcatchment water harvesting systems in Iran     

Hamid Reza Fooladmand  Ali Reza Sepaskhah   《Journal of Arid Environments》2004,58(4):478

An economic analysis was conducted for temporal yield variations of four local grape cultivars grown in rain-fed microcatchments in the Bajgah area of Fars province, in Islamic Republic of Iran. For this study, four local cultivars of grapes were considered. The cultivars examined were Black Rishbaba, Rotabi, Asgari and Black grapes. The soil type was a gravely loam with an average slope of 5–6%, in microcatchment systems, and in plots without microcatchments. Analysis of yield data with a multiple regression model indicated that a 9 m² (3×3 m) microcatchment area for each individual plant (vine) was the most appropriate area for vineyards in this region. The results also demonstrated that by using this area for each grapevine, yields (kg/ha) were 40% greater than yields obtained for vines in the standard vineyard (without microcatchments) in this area. Economic analysis was performed and the cost and income were compared for a depreciation period (life-span period) of 50 years and interest rate of 14%. The analysis showed that a microcatchment area of 9 m² is economically feasible. The Black Rishbaba rain-fed vines were the most suitable cultivar for this region. The benefit probabilities of rain-fed Black Rishbaba, Rotabi, Asgari and Black grapes with a microcatchment area of 9 m² and without such an area were 63.3% (i.e. two of 3 years), 52.4% (i.e. one of 2 years), 32.9% (i.e. one of 3 years), 13.3% (i.e. one of 8 years), and 59.5% (i.e. two of 3 years), 39.4% (i.e. two of 5 years), 31.8% (i.e. one of 3 years), and 10.7% (i.e. one of 9 years), respectively. Therefore, the Black Rishbaba and Rotabi cultivars are economically more stable in microcatchment system, while only the Black Rishbaba cultivar would be such in the standard vineyard system.  相似文献   

Wood storage in a wide mountain river: case study of the Czarny Dunajec,Polish Carpathians     

Bart&#x;omiej Wyga  Joanna Zawiejska 《地球表面变化过程与地形》2005,30(12):1475-1494

Storage of large woody debris in the wide, mountain, Czarny Dunajec River, southern Poland, was investigated following two floods of June and July 2001 with a seven‐year frequency. Within a reach, to which wood was delivered only by bank erosion and transport from upstream, wood quantities were estimated for eighty‐nine, 100 m long, channel segments grouped into nine sections of similar morphology. Results from regression analysis indicated the quantity of stored wood to be directly related to the length of eroded, wooded banks and river width, and inversely related to unit stream power at the flood peak. The largest quantities of wood (up to 33 t ha^?1) were stored in wide, multi‐thread river sections. Here, the relatively low transporting ability of the river facilitated deposition of transported wood while a considerable length of eroded channel and island banks resulted in a large number of trees delivered from the local riparian forest. In these sections, a few morphological and ecological situations led to the accumulation of especially large quantities of wood within a small river area. Very low amounts of wood were stored in narrow, single‐thread sections of regulated or bedrock channel. High stream power facilitated transport of wood through these sections while the high strength of the banks and low channel sinuosity prevented bank retreat and delivery of trees to the channel. Considerable differences in the character of deposited wood existed between wide, multi‐thread channel sections located at different distances below a narrow, 7 km long, channellized reach of the river. Wood deposited close to the downstream end of the channellized reach was highly disintegrated and structured into jams, whereas further downstream well preserved shrubs and trees prevailed. This apparently reflects differences in the distance of wood transport and shows that in a mountain river wider than the height of trees growing on its banks, wood can be transported long distances along relatively narrow, single‐thread reaches but is preferentially deposited in wide, multi‐thread reaches. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Electrodialytic remediation of CCA-treated waste wood in pilot scale     

Anne J. Pedersen  Iben V. Kristensen  Lisbeth M. Ottosen  Alexandra B. Ribeiro  Arne Villumsen 《Engineering Geology》2005,77(3-4):331-338

When chromated copper arsenate (CCA)-treated wood is removed from service and turns into waste, the contents of Cu, Cr and As remain high due to the strong fixation of CCA in the wood. This high content of toxic compounds presents a disposal challenge. Incineration of CCA-treated waste wood is not allowed in Denmark; instead, the wood is to be land-filled until new methods for handling the wood are available. Since the amounts of CCA-treated wood being removed from service is expected to increase in the years to come, the need for finding alternative handling methods is very relevant. In this study, the usefulness of Electrodialytic Remediation was demonstrated for handling of CCA-treated waste wood in pilot scale. The electrodialytic remediation method, which uses a low-level direct current (DC) as the cleaning agent, combines electrokinetic movement of ions in the wood matrix with the principles of electrodialysis. It has previously been shown that it is possible to remove Cu, Cr and As from CCA-treated wood using electrodialytic remediation in laboratory scale, but until now, the method had not been studied in large scale. The pilot-scale plant used in this study was designed to contain up to 2 m³ wood chips. Six remediation experiments were carried out. In these experiments, the process was up-scaled stepwise by increasing the distance between the electrodes from initially 60 cm to finally 150 cm. The remediation time was varied between 11 and 21 days, and phosphoric acid and/or oxalic acid was used to facilitate the desorption of CCA from the wood. In the most successful of the experiments carried out, the concentration of CCA in the wood was reduced by up to 82% for Cr, 88% for Cu and at least 96% for As.  相似文献   

The first evidence of paleo-wildfire from the Campanian (Late Cretaceous) of North Africa     

《Cretaceous Research》2016

Although the fossil record of plant macro- and mesofossils, including fossil charcoal, is patchy geographically and temporally, such remains play an important role for the interpretation of paleoenvironmental and paleoclimatic developments in the continental realm. In Egypt, previous palynological studies on the Upper Cretaceous (Campanian) deposits suggested presence of lush subtropical forests, dominated by angiosperms and pteridophytes, which developed under warm and wet climatic conditions. In the present study, the occurrence of paleo-wildfires during the Late Cretaceous (Campanian) is presented for the first time, based on samples from a surface exposure in the vicinity of the Baris Oasis, south Western Desert, Egypt. Macroscopic charcoal was collected and subsequently analyzed under a stereomicroscope and scanning electron microscope (SEM). The charred wood remains were identified as belonging to gymnosperms, which were important components of the North African paleoflora during the Cretaceous. These charcoal remains represent the first verified occurrence of paleo-wildfires in Africa during the Campanian.  相似文献   

延庆千家店地区硅化木赋存层位及形成时代分析     

焦润成  王荣荣  张淑云 《城市地质》2016,(2):56-59

北京延庆千家店土城子组中的硅化木自发现以来,得到了众多学者的关注,但关于硅化木的赋存层位和形成时代一直未有定论,目前主流观点认为硅化木广泛发育于土城子组一段和二段的下部,关于其形成时代则自侏罗纪早期至白垩纪早期的论述均有,这种争论显然不利于木化石的保护、科普和进一步深化认识。在千家店土城子组进行的考察结果展现出与前人观点不同的线索。实地考察、剖面测量和年龄测试结果显示:原位埋藏硅化木形成时代应为晚侏罗世早期,赋存层位为土城子组一段下部,而土城子组二段下部的沉积特征反应出当时水位频繁升降,水体能量剧烈变化,火山活动暂时陷入沉寂的沉积环境,较难满足形成木化石的基本要求。  相似文献   

Phylogenetic position and systematics of the wood‐associate limpet genus Caymanabyssia and implications for ecological radiation into deep‐sea organic substrates by lepetelloid gastropods          下载免费PDF全文

Yasunori Kano  Tsuyoshi Takano  Enrico Schwabe  Anders Warén 《Marine Ecology》2016,37(5):1116-1130

The gastropod superfamily Lepetelloidea represents an extremely diverse lineage in terms of their utilization of different deep‐sea organic substrates that include sunken wood, leaves, whale and fish bones, egg cases of sharks and rays, annelid tubes and detrital cephalopod beaks among others. They also inhabit cold seeps and hydrothermal vents, thus presenting an interesting case for the evaluation of such organic substrates as ‘stepping stones’ into these chemosynthetically nourished environments. Here we show the first molecular phylogeny of the Pseudococculinidae, a primarily wood‐dwelling family and the most speciose in Lepetelloidea. Special emphasis is placed on the genus Caymanabyssia, for which the only subfamily Caymanabyssiinae has been established, and a new species Caymanabyssia solis is described herein and compared with previously known taxa in order to reconsider the morphological characteristics of lepetelloids on wood. Bayesian and likelihood trees reconstructed using four‐gene sequences reveal that Pseudococculinidae sensu auctt. is a polyphyletic taxon that is grouped by shared plesiomorphic conditions of characters including the radula, a digestive organ, the morphology of which is often governed strongly by diet and feeding ecology. The newly reinterpreted families Pseudococculinidae and Caymanabyssiidae represent reciprocal sister clades as a basal radiation in Lepetelloidea. Sunken wood might thus have served as an ancestral habitat from which species on other substrates and vent and seep taxa were derived.  相似文献   

内蒙古科尔沁右翼中旗协和尔斯德中生代火山沉积地层时代研究          下载免费PDF全文

付俊彧  那福超  郑少林  钟辉  汪岩  宋维民  孙巍  杨帆 《中国地质》2018,45(1):129-140

内蒙古科尔沁右翼中旗协和尔斯德一带出露一套中生代地层,岩石组合主要为酸性火山碎屑岩、火山碎屑沉积岩夹碎屑沉积岩及酸性火山熔岩。1∶50000区调依据在该套地层上部层位发现的木化石组合确定其时代为中—晚侏罗世,结合岩石组合,将该套地层划分为上侏罗统满克头鄂博组。为了准确厘定该套地层时代,为木化石延限研究及区域生物地层划分对比提供依据,本次研究在低于产木化石层位的酸性火山碎屑岩中采取了锆石测年样品(LA-ICP-MS),获得锆石U-Pb年龄(165±1)Ma,时代为中侏罗世。同时采取了侵入该套地层的斑状细晶闪长岩测年样品,获得锆石年龄(131±1)Ma,限定了地层形成的上限年龄。根据岩性组合的区域对比、测年结果、木化石组合时限、地层产状特征,认为该套地层应划为中侏罗统新民组,是突泉火山-沉积盆地充填物的一部分。  相似文献   

Relational Agriculture: Gender,Sexuality, and Sustainability in U.S. Farming     

Isaac Sohn Leslie  Jaclyn Wypler  Michael Mayerfeld Bell 《社会与自然资源》2019,32(8):853-874

Although 97% of U.S. farms are “family-owned,” little research examines how gender and sexual relationships – inherent in familial dynamics – influence farmers’ practices and livelihoods. Gender and sexual dynamics – shaped by race and class – affect who is considered a farmer, land management decisions, and access to resources like land, subsidies, and knowledge. We use feminist and queer lenses to illuminate how today’s agricultural gender and sexual relations are not “natural,” but when left uninterrogated are constructed in ways that harm women and queer farmers while limiting potential to develop sustainable practices. Women and queer farmers also resist, “re-orienting” gender and sexual relations in ways that expand possibilities for achieving food justice and ecological sustainability. We offer “relational agriculture” as a tool for making visible and re-orienting gender and sexual relations on farms. Relational agriculture brings sexuality into food justice and demonstrates the centrality of gender and sexuality to agricultural sustainability.  相似文献   

山区农村土地利用转型与小农经济变迁耦合机理   总被引：1，自引：0，他引：1  

苏康传  杨庆媛  张佰林  张忠训 《地理研究》2019,38(2):399-413

通过山区土地利用转型与小农经济变迁的耦合关系分析,可以揭示山区人地关系的变化过程和机理。随着工业化、城镇化的快速推进,山区农村人地关系发生深刻变化,小农经济变迁驱动土地利用转型,土地利用转型进一步促进小农经济变迁。在阐述土地利用转型及小农经济变迁内涵和特征基础上,结合实证探讨二者间的耦合机理,以期为乡村振兴战略的实施提供理论支撑和现实参考。研究表明：① 山区农村土地利用转型与小农经济变迁相互影响,耦合演进。② 山区农村土地利用转型重点体现在农村宅基地、耕地及林地三类用地上。③ 中国小农经济已发生四次变迁,而山区小农经济变迁在第四次中表现较为明显,其阶段特征主要为农村人口向城镇迁移,土地流转频繁,土地规模经营趋势增强。④ 山区小农经济变迁引发耕地空间形态及功能转型,山区耕地转型进一步促进小农经济变迁。⑤ 山区小农经济变迁及农户生计策略非农化转变促使农户对宅基地结构及功能的需求发生变化;闲置废弃宅基地综合整治可显化农村土地资产价值,增加农民土地财产性收入,促进小农经济变迁。⑥ 通过云南省砚山县耕地利用转型案例剖析,验证了本文提出的山区农村土地利用转型与小农经济变迁的耦合机理。  相似文献