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51.
This paper analyses the factors that control rates and extent of soil erosion processes in the 199 ha May Zegzeg catchment near Hagere Selam in the Tigray Highlands (Northern Ethiopia). This catchment, characterized by high elevations (2100–2650 m a.s.l.) and a subhorizontal structural relief, is typical for the Northern Ethiopian Highlands. Soil loss rates due to various erosion processes, as well as sediment yield rates and rates of sediment deposition within the catchment (essentially induced by recent soil conservation activities), were measured using a range of geomorphological methods. The area‐weighted average rate of soil erosion by water in the catchment, measured over four years (1998–2001), is 14·8 t ha?1 y?1, which accounts for 98% of the change in potential energy of the landscape. Considering these soil loss rates by water, 28% is due to gully erosion. Other geomorphic processes, such as tillage erosion and rock fragment displacement by gravity and livestock trampling, are also important, either within certain land units, or for their impact on agricultural productivity. Estimated mean sediment deposition rate within the catchment equals 9·2 t ha?1 y?1. Calculated sediment yield (5·6 t ha?1 y?1) is similar to sediment yield measured in nearby catchments. Seventy‐four percent of total soil loss by sheet and rill erosion is trapped in exclosures and behind stone bunds. The anthropogenic factor is dominant in controlling present‐day erosion processes in the Northern Ethiopian Highlands. Human activities have led to an overall increase in erosion process intensities, but, through targeted interventions, rural society is now well on the way to control and reverse the degradation processes, as can be demonstrated through the sediment budget. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
52.
Tesfaye Haimanot Tarekegn Alemseged Tamiru Haile Tom Rientjes P. Reggiani Dinand Alkema 《International Journal of Applied Earth Observation and Geoinformation》2010
Flood modeling often provides inputs to flood hazard management. In the present work we studied the flooding characteristics in the data scarce region of the Lake Tana basin at the source of the Blue Nile River. The study required to integrate remote sensing, GIS with a two-dimensional (2D) module of the SOBEK flood model. The resolution of the topographic data in many areas, such as the Lake Tana region, is commonly too poor to support detailed 2D hydrodynamic modeling. To overcome such limitations, we used a Digital Elevation Model (DEM) which was generated from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image. A GIS procedure is developed to reconstruct the river terrain and channel bathymetry. The results revealed that a representation of the river terrain largely affects the simulated flood characteristics. Simulations indicate that effects of Lake Tana water levels propagate up to 13 km along the Ribb River. We conclude that a 15 m resolution ASTER DEM can serve as an input to detailed 2D hydrodynamic modeling in data scarce regions. However, for this purpose it is necessary to accurately reconstruct the river terrain geometry and flood plain topography based on ground observations by means of a river terrain model. 相似文献
53.
Richard W. Healy Sosina S. Haile David L. Parkhurst Scott R. Charlton 《Ground water》2018,56(5):810-815
Variably saturated groundwater flow, heat transport, and solute transport are important processes in environmental phenomena, such as the natural evolution of water chemistry of aquifers and streams, the storage of radioactive waste in a geologic repository, the contamination of water resources from acid‐rock drainage, and the geologic sequestration of carbon dioxide. Up to now, our ability to simulate these processes simultaneously with fully coupled reactive transport models has been limited to complex and often difficult‐to‐use models. To address the need for a simple and easy‐to‐use model, the VS2DRTI software package has been developed for simulating water flow, heat transport, and reactive solute transport through variably saturated porous media. The underlying numerical model, VS2DRT, was created by coupling the flow and transport capabilities of the VS2DT and VS2DH models with the equilibrium and kinetic reaction capabilities of PhreeqcRM. Flow capabilities include two‐dimensional, constant‐density, variably saturated flow; transport capabilities include both heat and multicomponent solute transport; and the reaction capabilities are a complete implementation of geochemical reactions of PHREEQC. The graphical user interface includes a preprocessor for building simulations and a postprocessor for visual display of simulation results. To demonstrate the simulation of multiple processes, the model is applied to a hypothetical example of injection of heated waste water to an aquifer with temperature‐dependent cation exchange. VS2DRTI is freely available public domain software. 相似文献
54.
eDNA (environmental DNA)是指从环境样品（水体、土壤、沉积物、空气、混合物等）中提取的DNA,是各种生物的DNA混合物,区别于传统从单物种样品中提取的DNA。eDNA监测是指从环境样品中提取DNA,用物种特异性引物或特定DNA metabarcoding引物对其进行扩增测序、分类学分析、相对丰度分析、功能预测等,以监测环境中是否存在某特定物种,或者获得环境中物种组成、群落结构、生态功能等相关信息。eDNA监测主要应用在特定物种监测检出、生物多样性调查评估、群落结构和功能分析、生态系统过程分析评估等领域。eDNA监测可以应用在陆地、水体、空气、器物表面、生物（内）表面等任何有可能存在不确定DNA的场景。因为eDNA监测的非侵入性、灵敏检出、大类群检出、易标准化方法与结果、低人力物力时间成本、结果可核查等特点,未来很有希望发展成为一种常规的物种监测、群落功能预测、生态过程分析的方法,对象可涵盖所有生境条件下的所有生物类群。但要实现这个图景,需要从普遍性和特殊性层面完成eDNA监测技术链条中10个关键环节的技术标准化：样品重复数设计、采样时间设计、采样点设计、采样方法设... 相似文献
55.
鱼产潜力可为渔业资源保护和管理提供科技支撑,传统的鱼产潜力估算方法在大型湖泊中往往成本高、采样率低、时效差.本研究基于2018—2020年非冰封期(5—10月)在青海湖的实测数据,通过提取和校对海洋水色遥感MODIS卫星数据反演产品(1 km分辨率)并结合垂向归纳模型(VGPM)构建了青海湖浮游植物初级生产力及鱼产潜力估算模型,估算的浮游植物初级生产力与实测值对比的平均相对误差小于25%.利用该模型估算2018—2020年非冰封期青海湖基于浮游植物初级生产力的鱼产潜力并分析其时空分布规律,结果显示青海湖鱼产潜力在5—10月呈现先增加后减少的季节波动规律,最大值出现在夏季(7—8月);空间分布上呈现湖心小,岸边及靠近入湖支流河口区域大的分布状态,全湖总鱼产潜力月均变化范围为2.5万~17.6万t.鱼产潜力的时空分布规律主要受气温、外源营养物质、裸鲤摄食等影响.研究表明青海湖非冰封期的鱼类资源承载力年累计值可达45.8万t,明显高于现有裸鲤资源的现存量和历史产量高峰值,表明青海湖仍然具备很大的鱼类资源承载力与增殖空间.本研究为同类型的大型高原湖泊基于卫星遥感的高效长期鱼产潜力监测估算提供了范例,为青海湖“封湖育鱼”政策制定和增殖放流保护决策提供参考. 相似文献
56.
Wakgari Furi Moumtaz Razack Tigistu Haile Tamiru A. Abiye Dagnachew Legesse 《Environmental Earth Sciences》2011,62(6):1323-1335
Rise of groundwater level becomes an emerging concern at Wonji irrigation field, Main Ethiopian Rift. An integrated study
based on geophysical resistivity methods is conducted at Wonji wetland to understand the link between irrigation water and
the shallow aquifer system as well as to confirm the current concern of groundwater rise. The study was also intended to improve
the uncertainty of understanding the hydrogeology of Wonji wetland including the extent and direction of groundwater–surface
water interaction. The vertical and horizontal contacts between the different geological series of the Wonji area are resolved
with 2D high-resolution geophysical imaging. Results from both VES and 2D tomography show low resistivity layers under Wonji
irrigation field with narrow ranges in resistivity variation which corresponds to a homogeneous saturated layer. The geoelectric
sections reveal two fault systems running NW–SE and N–S directions which impede lateral groundwater flow. Furthermore, groundwater
is converged towards the Wonji irrigation site strained by these fault systems. The geophysical results show strong link between
irrigation water and the shallow unconfined aquifer as well as among the local and regional flow systems. 相似文献
57.
Amaury Frankl Jean Poesen Nelles Scholiers Miró Jacob Mitiku Haile Jozef Deckers Jan Nyssen 《地球表面变化过程与地形》2013,38(14):1672-1684
Small‐scale aerial photographs and high‐resolution satellite images, available for Ethiopia since the second half of the twentieth century as for most countries, allow only the length of gullies to be determined. Understanding the development of gully volumes therefore requires that empirical relations between gully volume (V) and length (L) are established in the field. So far, such V–L relations have been proposed for a limited number of gullies/environments and were especially developed for ephemeral gullies. In this study, V–L relations were established for permanent gullies in northern Ethiopia, having a total length of 152 km. In order to take the regional variability in environmental characteristics into account, factors that control gully cross‐sectional morphology were studied from 811 cross‐sections. This indicated that the lithology and the presence of check dams or low‐active channels were the most important controls of gully cross‐sectional shape and size. Cross‐sectional size could be fairly well predicted by their drainage area. The V–L relation for the complete dataset was V = 0 · 562 L 1·381 (n = 33, r2 = 0 · 94, with 34 · 9% of the network having check dams and/or being low‐active). Producing such relations for the different lithologies and percentages of the gully network having check dams and/or being low‐active allows historical gully development from historical remote sensing data to be assessed. In addition, gully volume was also related to its catchments area (A) and catchment slope gradient (Sc). This study demonstrates that V–L and V–A × Sc relations can be very suitable for planners to assess gully volume, but that the establishment of such relations is necessarily region‐specific. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
58.
Katrien Descheemaeker Jean Poesen Lorenzo Borselli Jan Nyssen Dirk Raes Mitiku Haile Bart Muys Jozef Deckers 《水文研究》2008,22(20):4097-4105
Daily runoff from 27 plots (5 m × 2 m) recorded during two rainy seasons in the Tigray highlands (Ethiopia) were analysed together with daily rainfall to calculate runoff curve numbers for hillslopes covered by semi‐natural vegetation in varying stages of vegetation restoration. Curve number model parameters were derived using a least squares fitting procedure on the collected rainfall–runoff datasets. Curve numbers varied from 29 to 97. Land use type was an important explanatory factor for the variation in curve numbers, whereas hydrologic soil group was not. Curve numbers were negatively correlated with vegetation cover. Taking into account antecedent soil moisture conditions did not improve runoff prediction using the curve number method. As runoff prediction was less accurate in areas with low curve numbers, two separate regression functions relating curve numbers with vegetation cover were proposed for different land use types. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
59.
Limited availability of surface‐based rainfall observations constrains the evaluation of satellite rainfall products over many regions. Observations are also often not available at time scales to allow evaluation of satellite products at their finest resolutions. In the present study, we utilized a 3‐month rainfall data set from an experimental network of eight automatic gauges in Gilgel Abbay watershed in Ethiopia to evaluate the 1‐hourly, 8 × 8‐km Climate Prediction Center morphing technique (CMORPH) rainfall product. The watershed is situated in the Lake Tana basin which is the source of the Blue Nile River. We applied a suite of statistical metrics that included mean difference, bias, standard deviation of differences and measures of association. Our results indicate that the accuracy of the CMORPH product shows a significant variation across the basin area. Its estimates are mostly within ±10 mm h?1 of the gauge rainfall observations; however, the product does not satisfactorily capture the rainfall temporal variability and is poorly correlated (<0.27) to gauge observations. Its poor rain detection capability led to significant underestimation of the seasonal rainfall depth (total bias reaches up to ?52%) with large amounts of hit rain bias as well as missed rain and false rain biases. In the future refinement of CMORPH algorithm, more attention should be given to reducing missed rain bias over the mountains of Gilgel Abbay, whereas equal attention should be given to hit, missed rain and false rain biases over other parts of the watershed. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
60.
Water relations of four tree species were studied in four sites in the drylands of northern Ethiopia. Predawn water potentials were significantly higher at all sites as compared to midday measurements for Acacia etbaica and Boswellia papyrifera. In contrast, Lannea fruticosa revealed this significant difference only once, while Terminalia brownii at only two of the four sites. An analysis of variance showed that A. etbaica has a wider tolerance range as compared to the other species. There was no significant difference among the four sites in terms of predawn, midday and diurnal ranges of water potential. The study revealed that A. etbaica and B. papyrifera are performing better as compared to T. brownii and L. fruticosa under the current climatic conditions. Understanding the physiological basis of survival, productivity, ability to cope with low moisture availability, and growth potential of indigenous species in the drylands is essential for the utilization and promotion of these and other species. 相似文献