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Spatial patterns of old, deep-seated landslides: A case-study in the northern Ethiopian highlands 总被引：1，自引：0，他引：1
M. Van Den Eeckhaut J. Moeyersons J. Nyssen Amanuel Abraha J. Poesen Mitiku Haile J. Deckers 《Geomorphology》2009,105(3-4):239-252
During the last decade, slope failures were reported in a 500 km2 study area in the Geba–Werei catchment, northern Ethiopia, a region where landslides were not considered an important hazard before. Field observations, however, revealed that many of the failures were actually reactivations of old deep-seated landslides after land use changes. Therefore, this study was conducted (1) to explore the importance of environmental factors controlling landslide occurrence and (2) to estimate future landslide susceptibility. A landslide inventory map of the study area derived from aerial photograph interpretation and field checks shows the location of 57 landslides and six zones with multiple landslides, mainly complex slides and debris flows. In total 14.8% of the area is affected by an old landslide. For the landslide susceptibility modelling, weights of evidence (WofE), was applied and five different models were produced. After comparison of the models and spatial validation using Receiver Operating Characteristic curves and Kappa values, a model combining data on elevation, hillslope gradient, aspect, geology and distance to faults was selected. This model confirmed our hypothesis that deep-seated landslides are located on hillslopes with a moderate slope gradient (i.e. 5°–13°). The depletion areas are expected on and along the border of plateaus where weathered basalts rich in smectite clays are found, and the landslide debris is expected to accumulate on the Amba Aradam sandstone and upper Antalo limestone. As future landslides are believed to occur on inherently unstable hillslopes similar to those where deep-seated landslides occurred, the classified landslide susceptibility map allows delineating zones where human interventions decreasing slope stability might cause slope failures. The results obtained demonstrate that the applied methodology could be used in similar areas where information on the location of landslides is essential for present-day hazard analysis. 相似文献
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A study was made of the water chemistry, tissue nutrients and surface phosphatase activities of the 2-cm apices of three mosses in four upland streams in northern England, UK. This was part of a project to optimize methods for assessing nutrient fractions in environments with highly variable water chemistry. Aqueous N and P fractions showed the greatest variability followed by moss phosphatase activities, with nutrient composition of the shoot apices the least variable. There was no consistent pattern as to which aqueous N or P fraction was the most variable. The ratio between total inorganic N and total filtrable P ranged over three orders of magnitude in some streams. The interrelations between tissue N and P concentrations, tissue N:P ratio, phosphatase activities and aqueous variables showed:
- (1) Significant +ve relationship between tissue N and aqueous NO3–N in some populations, but not between tissue P and aqueous P concentration;
(2) Significant +ve relationships between phosphatase activities and aqueous organic N, but none with aqueous organic P;
(3) Significant +ve relationships between phosphodiesterase:phosphomonoesterase activities and aqueous organic N;
(4) Significant −ve relationships between phosphatase activities and tissue P concentration;
(5) Significant +ve relationships between phosphatase activities and tissue N:P.
Both types of biological measurement are valuable for monitoring ambient nutrients in upland streams. Neither is clearly better than the other, so both should be included in surveys. 相似文献
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Alemseged Tamiru Haile Ashenafi Lekasa Akawka Beza Berhanu Tom Rientjes 《水文科学杂志》2017,62(13):2139-2149
Climatic and hydrological changes will likely be intensified in the Upper Blue Nile (UBN) basin by the effects of global warming. The extent of such effects for representative concentration pathways (RCP) climate scenarios is unknown. We evaluated projected changes in rainfall and evapotranspiration and related impacts on water availability in the UBN under the RCP4.5 scenario. We used dynamically downscaled outputs from six global circulation models (GCMs) with unprecedented spatial resolution for the UBN. Systematic errors of these outputs were corrected and followed by runoff modelling by the HBV (Hydrologiska ByrånsVattenbalansavdelning) model, which was successfully validated for 17 catchments. Results show that the UBN annual rainfall amount will change by ?2.8 to 2.7% with a likely increase in annual potential evapotranspiration (in 2041–2070) for the RCP4.5 scenario. These changes are season dependent and will result in a likely decline in streamflow and an increase in soil moisture deficit in the basin. 相似文献
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三十多年来,人们对水生野生动物保护中的保护地建设、迁地保护、人工保种、人工驯养、人工繁育、人工养殖、增殖放流、生态修复等保护方式一直存在着激烈的争论.这反映了人们对水生野生动物保护目标、保护方式认识不一致甚至对立的问题,而其根本在于缺乏一个能够适应水生野生动物保护需求和特征的理论话语体系.本文基于对水生野生动物保护目标认知和设置的差异,基于对水生野生动物保护中人工干预方式的差异,尝试以“物种保护与生态保护”、“主动保护与被动保护”两个维度为框架建立水生野生动物保护的理论话语体系,然后着重分析水生野生动物物种保护中的主动保护与被动保护的状况与成效,指出部分水生野生动物保护地由于其整体生态格局已被改变或依然处于恶化的趋势中,并且无法避免人类活动的干扰和影响,导致了相应水生野生动物的就地保护效果不理想,而获得足够主动保护努力介入的物种在获得人工保种、人工繁育、人工养殖之后,其物种灭绝的风险已基本解除,甚至部分已野外绝迹物种还存在野外种群重建的机会.而后,以长江三种鲟鱼的保护和效果为例,对比展示了主动保护对于水生野生动物保护的必要性.建议就水生野生动物保护而言,在不遗余力抓保护地建设等被动保护的同时,更要积极地推动人工繁育、人工养殖等主动保护来对物种兜底. 相似文献
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Biadgilgn Demissie Jan Nyssen Paolo Billi Mitiku Haile Veerle Vaneetvelde Amaury Frankl 《自然地理学》2019,40(1):71-90
This paper investigates land-use/cover changes related to river dynamics in northern Ethiopia. Aerial photographs from 1965 to 1986, and SPOT images of 2007 and 2014 were used to extract land units. Land-use/cover changes took place in 48% of the entire landscape around the river across the last five decades. Changes related to swap accounted for 37%, whereas net changes accounted for 11%. The most systematic transitions in terms of gain were from shrubland to farmland, alluvial deposit to settlement, and alluvial deposit to active channel and settlement. Most of these transitions were related to the river dynamics and depict cyclic transitions: farmland → active channel → alluvial deposits → grassland/shrubland → farmland. Human interventions and natural vegetation succession were also very important. The study concludes that river systems have considerable impact on livelihood and need attention in land management undertakings in graben bottoms. 相似文献
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Boswellia papyrifera (Del) Hochst is a key dry land plant species in the Horn of Africa with high socio-economic significance in Ethiopia, Eritrea and Sudan. In recent decades, populations of this species are declining due to lack of recruitment through natural regeneration. This study investigated the potential of vegetative propagation using leafless branch cuttings as an alternative means of reproduction for the species. The effect of time of collection and cutting sizes (length and thickness) on shooting and rooting of the cuttings was investigated. The effects of these three factors were analysed, two-by-two, in three separate factorial experiments each arranged in a randomized complete block design. Time of collection affected cutting performance: shooting percent, shoot number, cutting vigour, leaf number, leaf length, rooting percent and root length were best when cuttings were collected in February-March, and weakest in May. Medium to long cuttings (1.0 m-2.0 m) and thicker cuttings (0.19-0.27 m) performed better than shorter or thinner cuttings. These results indicate that B. papyrifera is amenable to macro-propagation via leafless branch cuttings. Reproduction of B. papyrifera through macro-propagation may help overcome the population recruitment bottleneck of this important species and will help the long-term yield possibilities of its precious product frankincense. 相似文献
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This paper presents the enrichment tendency and spatial distribution of metals in the groundwater which is pumped out from the granitic aquifers in South Africa. Groundwater is the sole source of water supply for the local community in the study area (Namaqualand), and hence, it was necessary to understand the controlling geochemical processes and interrelationship of metals in the groundwater. The geochemical association of metals has been assessed based on the geostatistical methods. The results show that geochemical processes such as oxidation, leaching, and evaporation besides water–rock interaction are very important in controlling metal enrichment in the groundwater from highly mineralized rocks. The metal enrichment index for selected toxic metals in groundwater increases in the order of Cd > U > Cr > Pb. The observed enrichment trend could be considered as a result of mineralization of basement rocks which is facilitated by active geochemical process in the arid environment. The lack of aquifer flushing due to negligible recharge helps the metals to concentrate at shallow groundwater zones supported by severe evaporation process. 相似文献
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An online systematic error correction is presented and examined as a technique to improve the accuracy of real-time numerical weather prediction, based on the dataset of model errors(MEs) in past intervals. Given the analyses, the ME in each interval(6 h) between two analyses can be iteratively obtained by introducing an unknown tendency term into the prediction equation, shown in Part I of this two-paper series. In this part, after analyzing the 5-year(2001–2005) GRAPESGFS(Global Forecast System of the Global and Regional Assimilation and Prediction System) error patterns and evolution,a systematic model error correction is given based on the least-squares approach by firstly using the past MEs. To test the correction, we applied the approach in GRAPES-GFS for July 2009 and January 2010. The datasets associated with the initial condition and SST used in this study were based on NCEP(National Centers for Environmental Prediction) FNL(final) data.The results indicated that the Northern Hemispheric systematically underestimated equator-to-pole geopotential gradient and westerly wind of GRAPES-GFS were largely enhanced, and the biases of temperature and wind in the tropics were strongly reduced. Therefore, the correction results in a more skillful forecast with lower mean bias and root-mean-square error and higher anomaly correlation coefficient. 相似文献