Impacts of artisanal gold mining systems on soil and woody vegetation in the semi‐arid environment of northern Ethiopia          下载免费PDF全文

Hailemariam Meaza  Mushir Ali  Zbelo Tesfamariam  Niguse Abebe 《Singapore journal of tropical geography》2017,38(3):386-401

Gold mining is a tremendously important economic activity in rural districts of Ethiopia. We assessed the impacts of artisanal gold mining on soil and woody vegetation in northern Ethiopia. Estimation of soil loss, plant inventory, group discussions and transect studies were used to address the research questions. We employed t‐test to compare woody species and soil loss between mined and unmined sites. Moreover, we ran one‐way ANOVA to compare the average volume of soil loss among the mining sites. The study shows that gold mining removed colossal volumes of soil from the mining landscape with a significant difference among gold mining sites (P ≤ 0.05). Soil loss between the mined and unmined sites was also significant (P ≤ 0.05). Moreover, gold mining destroyed massive tracts of vegetation. Woody species encountered at plot level decreased from artisanal gold mined to unmined sites (P ≤ 0.05). Moreover, dead trees and exposed tree roots were higher in mined than the unmined areas (P ≤ 0.05). This discouraged regeneration and recruitment of woody vegetation. To conclude, gold mining system converted vegetated sites and farmlands into dysfunctional landscape. Therefore, we suggest that combined rehabilitation efforts are required to overcome the challenges of artisanal gold mining on sustainable land management in northern Ethiopia.  相似文献   

埃塞俄比亚阿迪戴斯塔VSHMS型铜锌矿床地质特征          下载免费PDF全文

高长亮  党万民  刘鹏磊  吕涛  高志友  陈永昊  张勇  高荣政  高昕旸 《山东国土资源》2016,32(6)

VSHMS型矿床是近年来研究块状硫化物矿床的新动向,埃塞俄比亚北部阿迪戴斯塔矿床为一个铜锌异体共生、伴生银的大型VSHMS型铜锌多金属矿床,通过对该矿床的区域地质背景、矿区地质、矿床地质特征的研究,指出铜锌矿床赋矿地层为新元古代特沙里特浅变质火山-沉积岩群,矿带具有"双色蚀变带"特征,并与典型VSHMS型矿床对比,初步探讨该矿床的成因类型及成矿模式。  相似文献   

Use of the revised universal soil loss equation (RUSLE) for soil and nutrient loss estimation in long-used rainfed agricultural lands,North Ethiopia   总被引：1，自引：1，他引：0  

Berhane Lema  Fassil Kebede  Ibrahim Fitiwy  Zenebe Abraha 《自然地理学》2016,37(3-4):276-290

This study was conducted to quantify agricultural land degradation in the Ruba Gered watershed, Ethiopia. The watershed was divided into 12 land mapping units (LMU) after superimposing maps of soil, slope, land use/cover, and elevation. Subsequently, cultivated land was delineated to assess degradation types and severity based on standard approaches. Sheet erosion was estimated using the revised universal soil loss equation. Composite soil samples were collected from each LMU to quantify key soil nutrients (OM, total nitrogen, available phosphorus, and available potassium) lost by sheet erosion. The annual average soil loss due to sheet erosion was estimated to be 17.4 t ha^?1 yr^?1, with average annual nutrient losses estimated as 246.5 kg ha^?1 organic matter, 12.4 kg ha^?1 total nitrogen, 0.1 kg ha^?1 available phosphorus, and 1.6 kg ha^?1 available potassium. The study revealed that substantial quantities of soil and nutrients are lost every year in the study area due to severe sheet erosion. This amount of nutrient loss severely degrades soil and reduces soil fertility.  相似文献   

Long-term resilience, bush encroachment patterns and local knowledge in a Northeast African savanna     

Graciela Gil-Romera  Henry F. Lamb  David Turton  Miguel Sevilla-Callejo  Mohammed Umer 《Global Environmental Change》2010,20(4):612-626

Bush encroachment is a significant phenomenon in savanna environments as it affects wildlife and local livelihoods by preventing new pasture generation. In this article we present a 2000-year record of vegetation change in the Dara range of the Mago National Park, southwestern Ethiopia, an area inhabited by Mursi agro-pastoralists. We use an interdisciplinary approach to understand whether bush encroachment in this area is a recent event or a transitional state of the savanna and describe the local understanding of encroachment as a species-specific process. The vegetation record was obtained from a fossil hyrax midden, a type of sediment already used in Southern Africa but never before in East Africa. Six encroaching phases, led by Capparaceae and Grewia, were found over the last two millennia. The system proved to be resilient, with alternating open and encroached phases, and showed a non-linear response to environmental change, thereby fitting the control theory hypothesis for hysteresis loops. Determining the thresholds conditioning the system's resilience could help to improve savanna management for both local people and National Park authorities.  相似文献   

Stable carbon isotope ratios in tree rings of co-occurring species from semi-arid tropics in Africa: Patterns and climatic signals     

Aster Gebrekirstos  Martin Worbes  Demel Teketay  Masresha Fetene  Ralph Mitlhner 《Global and Planetary Change》2009,66(3-4):253-260

Although several proxies have been proposed to trace the course of environmental and climatological fluctuations, precise paleoclimate records from the tropics, notably from Africa are still sorely lacking today. Stable carbon isotopes (δ¹³C) in tree rings are an attractive record of climate. In this study, the patterns and climatic signals of δ¹³C ratios were determined on tree rings of deciduous (Acacia senegal, Acacia tortilis, Acacia seyal) and an evergreen (Balanites aegyptiaca) species, from a semi-arid Acacia Woodland in Ethiopia. δ¹³C inter-annual patterns are synchronous among the co-occurring species. A declining trend with time was observed in δ¹³C, notably for B. aegyptiaca, which could be due to anthropogenic increases in atmospheric CO₂ concentration and decrease in atmospheric δ¹³C. Tree ring δ¹³C values of all the species revealed significant negative correlation with precipitation amount but not with temperature and relative humidity. The δ¹³C series of the deciduous species shows a higher correlation (r = − 0.70 to − 0.78) with precipitation than the evergreen species (r = − 0.55). A master δ¹³C series, composed of the average of the three Acacia species, displayed stronger significant correlation (r = − 0.82) than any of the individual species δ¹³C series. The weak relationship between temperature and δ¹³C in this study indicates that photosynthetic rate is not a significant factor. Moisture stress, however, may have a direct impact on the stomatal conductance and explain the strong negative relationship between δ¹³C and precipitation. The results demonstrate the potential of δ¹³C in tree rings to reflect physiological responses to environmental changes as a vehicle for paleoclimatic reconstruction, which is important to understand tree response to past and future climate change.  相似文献   

Volcanic vents rooted on extension fractures and their geodynamic implications in the Ethiopian Rift     

Tesfaye Korme  Jean Chorowicz  Bernard Collet  Franco F. Bonavia 《Journal of Volcanology and Geothermal Research》1997,79(3-4)

Most of the extension fractures located in the Ethiopian rift are related to rift dynamics, and they have consistently similar orientations for hundreds of kilometers. The orientation of extension fracture gives the local extension direction which is perpendicular to its horns (end segments of an extension fracture). We have established clear geometrical relationships between tectonics and volcanism in the Main Ethiopian Rift by interpreting high-resolution images obtained from Landsat-TM and SPOT satellites and by quantitatively analyzing the geometry of extension fractures, elongated vents and linear volcanic clusters. Applying the relationships obtained, we show that extension fractures in the rift served as channels for magma rising to the surface, and that extension fractures underlie most of the elongated volcanic vents and linear volcanic clusters. The geometry of extension fractures beneath volcanic edifices can be deduced from the shape of elongated vents and pattern of linear volcanic clusters rooted on them. Utilizing the orientations of extension fractures directly observed and those inferred from elongated volcanic vents and linear clusters, we found that the extension direction of the Main Ethiopian Rift is northwest–southeast and that the direction has been rotated clockwise for about 20° in the time interval 2.83 to 0.023 Ma. The Recent axis of rift opening is oriented N40° and located closer to the southeastern escarpment giving an asymmetric geometry to the Main Ethiopian Rift (MER).  相似文献   

Planation surfaces in Northern Ethiopia   总被引：3，自引：0，他引：3  

M. Coltorti  F. Dramis  C.D. Ollier   《Geomorphology》2007,89(3-4):287-296

Planation surfaces are an old-fashioned topic in geomorphology, but they are nevertheless important where they make up much of the landscape. Northern Ethiopia is largely a stepped topography, caused by differential erosion. Exhumation of old planation surfaces that were preserved under sedimentary or volcanic cover is an important process in landscape evolution. The oldest planation surface is of early Palaeozoic age (PS1); the second is Late Triassic (PS2); and the third is of Early Cretaceous age (PS3). The Oligocene Trap Volcanics buried a surface (PS4) of early Tertiary age, which is now widely exposed by erosion as a surface that, where flat enough, is an exhumed planation surface. The surfaces do not relate to the supposed Africa-wide pediplain sequence of King [King, L.C., 1975. Planation surfaces upon highlands. Z. Geomorph. NF 20 (2), 133–148.], either in mode of formation and age. Although the region is tropical, there is scarce evidence of deep weathering and few indications that the surfaces could be regarded as etchplains. These surfaces indicate that eastern Africa underwent long episodes of tectonic quiescence during which erosion processes were able to planate the surface at altitudes not too far from sea level. Only after the onset of rifting processes, uplift became active and transformed a vast lowland plain into the present Ethiopian highlands, largely exceeding 2500 m a.s.l. Some hypotheses and speculations on the genesis of these surfaces are considered here.  相似文献   

Reservoir siltation in the semi‐arid highlands of northern Ethiopia: sediment yield–catchment area relationship and a semi‐quantitative approach for predicting sediment yield     

L. Tamene  S. J. Park  R. Dikau  P. L. G. Vlek 《地球表面变化过程与地形》2006,31(11):1364-1383

Due to shortage of rainfall and its increasing variability, moisture stress is identified to be one of the most critical factors affecting agricultural productivity in the drylands of Ethiopia. To circumvent this problem, a strategy of supplemental irrigation through surface water harvesting was adopted by the government and several micro‐dams have been built in the semi‐arid parts of the country. However, the benefits from the water harvesting schemes are not sustainable because of rapid water storage loss due to siltation. There is, therefore, an urgent need for improved catchment‐based erosion control and sediment management strategies. The design and implementation of such strategies require data on the rate and magnitude of sediment deposition. To this end, reservoir surveys were conducted to estimate sediment deposition rate for 11 reservoirs identified to be representative of catchments in the Tigray region of northern Ethiopia. Two approaches were employed during the survey: one was based on measurement of sediment thickness in reservoirs while the other was based on comparing the original and existing topography of the reservoir‐beds. The average annual sediment yield estimated for the study sites was about 19 t ha^?1 y^?1. An equation of the type SSY = 3á36A^0á67 (with SSY = area specific sediment yield in t ha^?1 y^?1 and A = catchment area in km²) was also established for the study region, which is opposite to the ‘universal’ SSY–A relationship. In order to improve the sediment yield predictive capability of A, it was integrated with a factorial index that assesses the catchment's propensity to erosion and potential sediment yield. The effect of accelerated sediment deposition on water storage loss of reservoirs and possible controlling factors of the SSY–A relationship are outlined. The potential semi‐quantitative scoring approach to characterize catchments in terms of erosion sensitivity and the significance of the A‐index approach to predict SSY of similar catchments are also highlighted. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

The use of plant water relations to characterize tree species and sites in the drylands of northern Ethiopia     

K. Gebrehiwot  B. Muys  M. Haile  R. Mitloehner 《Journal of Arid Environments》2005,60(4):581-592

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   

Geology and mineral potential of Ethiopia: a note on geology and mineral map of Ethiopia   总被引：1，自引：0，他引：1  

Solomon Tadesse  Jean-Pierre Milesi  Yves Deschamps   《Journal of African Earth Sciences》2003,36(4):273-313

This work presents a geoscientific map and database for geology, mineral and energy resources of Ethiopia in a digital form at a scale of 1:2,000,000, compiled from several sources. The final result of the work has been recorded on CD-ROM in GIS format so that the map and the database could be available to users on a personal computer.Metallic resources (precious, rare, base and ferrous–ferroalloy metals) are widely related to the metamorphic meta-volcano-sedimentary belts and associated intrusives belonging to various terranes of the Arabian–Nubian Shield, accreted during the East and West Gondwana collision (Neoproterozoic, 900–500 Ma).Industrial minerals and rock resources occur in more diversified geological environments, including the Proterozoic basement rocks, the Late Paleozoic to Mesozoic sediments and recent (Cenozoic) volcanics and associated sediments.Energy resources (oil, coal, geothermal resources) are restricted to Phanerozoic basin sediments and Cenozoic volcanism and rifting areas.  相似文献