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1.
Daniel Meshesha Ryuichi Shinjo Risa Matsumura Takele Chekol 《Contributions to Mineralogy and Petrology》2011,162(5):889-907
Mantle xenoliths entrained in Quaternary alkaline basalts from the Turkana Depression in southern Ethiopia (the East Africa
Rift) were studied for their geochemical and Sr–Nd–Pb isotopic compositions to constrain the evolution of the lithosphere.
The investigated mantle xenoliths are spinel lherzolites in composition with a protogranular texture. They can be classified
into two types: anhydrous and hydrous spinel lherzolites; the latter group characterized by the occurrences of pargasite and
phlogopite. The compositions of whole-rock basaltic component (CaO = 3.8–5.6 wt%, Al2O3 = 2.5–4.1 wt%, and MgO = 34.7–38.1 wt%), spinel (Cr# = 0.062–0.117, Al2O3 = 59.0–64.4 wt%) and clinopyroxene (Mg# = 88.4–91.7, Al2O3 = 5.2–6.7 wt%) indicate that the lherzolites are fertile and have not experienced significant partial melting. Both types
are characterized by depleted 87Sr/86Sr (0.70180–0.70295) and high 143Nd/144Nd (0.51299–0.51348) with wide ranges of 206Pb/204Pb (17.86–19.68) isotopic compositions. The variations of geochemical and isotopic compositions can be explained by silicate
metasomatism induced by different degree of magma infiltrations from ascending mantle plume. The thermobarometric estimations
suggest that the spinel lherzolites were derived from depths of 50–70 km (15.6–22.2 kb) and entrained in the alkaline magma
at 847–1,052°C. Most of the spinel lherzolites from this study record an elevated geotherm (60–90 mW/m2) that is related to the presence of rising mantle plume in an active tectonic setting. Sm–Nd isotopic systematic gives a
mean TDM model age of 0.95 Ga, interpreted as the minimum depletion age of the subcontinental lithosphere beneath the region. 相似文献
2.
Anders Wästfelt Tsegaye TegenuMichael M. Nielsen Bo Malmberg 《Applied geography (Sevenoaks, England)》2012,32(2):465-476
Satellite images have enormous potential for qualitative land use analysis. This paper presents empirical results that demonstrate how normally invisible dimensions produced by land use can be identified by enriching satellite data with qualitative information from field studies.Land use can be defined as the intentional use of a specific piece of land resulting in patterns of ecological responses that are visible in the land cover and landscape. Responses to land use often result in a heterogeneous combination of reflectance in satellite images. Statistical methods used in the classification of satellite imagery are limited in their capacity to handle categories consisting of heterogeneous combinations of spectral values. To overcome this limitation, a contextual post-classification method has been used to map land cover configurations as related to different agricultural practices in the district of Sodo, Ethiopia.The results show that it is possible to map socio-spatial distribution of different agricultural and socioeconomic practices on a regional level by combining field observations and spatial contextual information. The empirical findings show local agricultural activity variations in cash crop production and subsistence agriculture in the Sodo district of Ethiopia. 相似文献
3.
Hailemariam Meaza Diress Tsegaye Jan Nyssen 《Norsk geografisk tidsskrift. Norwegian journal of geography》2016,70(1):1-12
In the northern highlands of Ethiopia degraded hillsides have been allocated to landless farmers for tree planting since the mid-1990s. The authors assessed the effect of hillside plantations on the livelihoods of landless farmers in the eastern part of the Tigray Region by using transect walks, focus group discussions, and pretested questionnaires. A matched-pairs design was used to compare crop yields, livestock holdings per household, and household incomes to test the differences before and eight years after the intervention. In addition, regression analysis was used to capture variables influencing hillside management. The findings revealed that the plantations significantly increased crop yields, livestock holdings, and the household incomes of all beneficiaries. In addition, tree planting on degraded hillsides had a positive impact on the livelihoods of formerly landless farmers. However, moisture stress and free-ranging livestock were crucial problems. The findings are highly relevant in a conservation context because many existing or planned hillside allocations to landless farmers are located on degraded steep slopes that are unsuitable for crop production. Thus, replicating the practice to other areas with similar environment and problems would be worthwhile, although the management should focus on careful planning to avoid conflicts of interest between beneficiaries and non-beneficiaries. 相似文献
4.
Mesenbet Yibeltal Atsushi Tsunekawa Nigussie Haregeweyn Enyew Adgo Derege Tsegaye Meshesha Tsugiyuki Masunaga Mitsuru Tsubo Paolo Billi Kindiye Ebabu Mulatu Liyew Berihun 《地球表面变化过程与地形》2021,46(6):1209-1222
Gully erosion is a major cause of soil loss and severe land degradation in sub-humid Ethiopia. The objective of this study was to investigate the role and the effect of subsurface water level change on gully headcut retreat, gully formation and expansion in high rainfall tropical regions in the Ethiopian highlands. During the rainy seasons of 2017–2019, the expansion rate of 16 fixed gullies was measured and subsurface water levels were measured by piezometers installed near gully heads. During the study period, headcut retreats ranged from 0.70 to 2.35 m, with a mean value of 1.49 ± 0.56 m year−1, and average depth of the surface water level varied between 1.12 and 2.82 m, with a mean value of 2.62 m. Gully cross-section areas ranged from 2.90 to 20.90 m2, with an average of 9.31 ± 4.80 m2. Volumetric retreat of gully headcuts ranged from 4.49 to 40.55 m3 and averaged 13.34 ± 9.10 m3. Soil loss from individual gullies ranged from 5.79 to 52.31 t year−1 and averaged 17.21 ± 11.74 t year−1. The headcut retreat rate and sediment yield were closely related over the three study seasons. Elevated subsurface water levels facilitated the slumping of gully banks and heads, causing high sediment yield. When the soil was saturated, bank collapse and headcut retreat were favoured by the combination of elevated subsurface water and high rainfall. This study indicates that area exclosures are effective in controlling subsurface water level, thus reducing gully headcut retreat and associated soil loss. 相似文献
5.
E. Aynekulu M. DenichD. Tsegaye R. AertsB. Neuwirth H.J. Boehmer 《Journal of Arid Environments》2011,75(5):499-503
Forests are highly susceptible to dieback under ongoing climate warming. In degraded forests, dead standing trees, or snags, have become such prominent features that they should be taken into account when setting management interventions. This study investigated (1) the extent and spatial pattern of standing dead stems of Juniperus procera and Olea europaea subsp. cuspidata along an elevational gradient, and (2) the effect of dieback on forest stand structure. We quantified abundance, size, and spatial pattern of tree dieback in 57 plots (50 m × 50 m) established at 100 m intervals along five transects. The snag density and basal area (mean ± SE) of the two species combined were 147 ± 23 stems ha−1 and 5.35 ± 0.81 m2 ha−1, respectively. The percentages of snags were extremely high for both J. procera (57 ± 7%) and O. europaea subsp. cuspidata (60 ± 5%), but showed a decreasing trend with increasing elevation suggesting that restoration is even more urgent at the lower elevations. Snags of the two species accounted for 31 and 45% of total stand density and basal area, respectively. Living stems exhibited truncated inverse-J-shaped diameter and height class distributions, indicating serious regeneration problems of these foundation species in the study area. In addition to direct interventions to assist recruitment of climax tree species, sites with high dieback would probably benefit from snag reduction to prevent fire incidents in the remaining dry Afromontane forests in northern Ethiopia. 相似文献
6.
7.
Analyzing the runoff response to soil and water conservation measures in a tropical humid Ethiopian highland 总被引：1，自引：0，他引：1
Dagnenet Sultan Atsushi Tsunekawa Nigussie Haregeweyn Enyew Adgo Mitsuru Tsubo Derege Tsegaye Meshesha 《自然地理学》2013,34(5):423-447
AbstractDifferent soil and water conservation (SWC) practices have been implemented in many drought-prone parts of Ethiopia since the 1980s. We assessed the effect of SWC practices on runoff response and experimentally derived and tested the validity of the runoff curve number (CN) model parameter for the tropical humid highland climate of the Kasiry watershed in northwestern Ethiopia. We recorded daily rainfall and runoff depth from 18 runoff plots (30 m long × 6 m wide) representing the five main land-use types with various SWC practices and two slope classes (gentle and steep). CN values were derived using the lognormal geometric mean CN procedure. Runoff was significantly less from plots with SWC measures, with average reductions of 44 and 65% observed in cultivated and non-agricultural lands, respectively. Runoff on plots representing non-agricultural land was relatively accurately predicted with the derived CN method, but predictions were less accurate for plots treated with a SWC practice. We conclude that predicting the effect of SWC practices on runoff requires parameterization with separate sets of CN value for each SWC practice. 相似文献
8.
An isolated block of Precambrian basement rocks and Mesozoic sediments is exposed at Kella along the western margin of the Central Main Ethiopian Rift (MER), surrounded by Tertiary to Quaternary volcanic rocks. Apatite fission‐track thermochronology on two basement samples yielded ages of 7.2 ± 1.0 Ma and 6.7 ± 3.0 Ma and a long mean track length (>14.5 μm). Rapid Late Miocene cooling is attributed to denudation related to rifting. Despite the paucity of data, due to the absence of suitable lithologies in the area, our data confirm that the Central MER is younger than 8 Ma as recently proposed on the basis of field evidence and radiometric dating of volcanics. This implies that the Central MER formed after the Northern MER, indicating a diachronous development of this third arm of the Red Sea–Gulf of Aden–Ethiopian Rift system. Terra Nova, 00, 000–000, 2010 相似文献
9.
Yared A. Bayissa Tsegaye Tadesse Mark Svoboda Brian Wardlow Calvin Poulsen John Swigart 《地理信息系统科学与遥感》2019,56(5):718-748
Developing a robust drought monitoring tool is vital to mitigate the adverse impacts of drought. A drought monitoring system that integrates multiple agrometeorological variables into a single drought indicator is lacking in areas such as Ethiopia, which is extremely susceptible to this natural hazard. The overarching goal of this study is to develop a combined drought indicator (CDI-E) to monitor the spatial and temporal extents of historic agricultural drought events in Ethiopia. The CDI-E was developed by combining four satellite-based agrometeorological input parameters – the Standardized Precipitation Index (SPI), Land Surface Temperature (LST) anomaly, Standardized Normalized Difference Vegetation Index (stdNDVI) and Soil Moisture (SM) anomaly – for the period from 2001 to 2015. The method used to combine these indices is based on a quantitative approach that assigns a weight to each input parameter using Principal Component Analysis (PCA). The CDI-E results were evaluated using satellite-based gridded rainfall (3-month SPI) and crop yield data for 36 intra-country crop growing zones for a 15-year period (2001 to 2015). The evaluation was carried out for the main rainfall season, Kiremt (June-September), and the short rainfall season, Belg (February-May). The results showed that moderate to severe droughts were detected by the CDI-E across the food insecure regions reported by FEWS NET during Kiremt and Belg rainfall seasons. Relatively higher correlation coefficient values (r > 0.65) were obtained when CDI-E was compared with the 3-month SPI across the majority of Ethiopia. The spatial correlation analyses of CDI-E and cereal crop yields showed relatively good correlations (r > 0.5) in some of the crop growing zones in the northern, eastern and southwestern parts of the country. The CDI-E generally mapped the spatial and temporal patterns of historic drought and non-drought years and hence the CDI-E could potentially be used to develop an agricultural drought monitoring and early warning system in Ethiopia. Moreover, decision makers and donors may potentially use CDI-E to more accurately monitor crop yields across the food-insecure regions in Ethiopia. 相似文献
10.
We studied current recruitment failure of Dobera glabra, an important famine-food throughout the dryland parts of the Horn of Africa. The species has previously been found to have recalcitrant seeds, a strategy not common for plants in dryland areas. We experimentally tested (1) how germination capacity of D. glabra is affected by seed form, storage period and moisture under nursery conditions, and (2) how seed predation by vertebrate herbivore and seed exposure at germination site affect germination under field conditions in northern Afar rangelands, Ethiopia. D. glabra seeds that received either mulching or supplementary watering (3 days/week) had a higher germination success than controls. The seeds are probably desiccation sensitive since stored seeds had poor germination performance compared to fresh seeds. Seeds in the rangeland plots protected from herbivores had significantly higher germination success compared to open plots. Our findings demonstrate that seed predation and moisture limitation highly reduced the germinability of the recalcitrant D. glabra seeds, indicating that the species might have persisted due to past wetter periods and low herbivore density in dry environments. 相似文献