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1.
Detecting soil salinity changes and its impact on vegetation cover are necessary to understand the relationships between these changes in vegetation cover. This study aims to determine the changes in soil salinity and vegetation cover in Al Hassa Oasis over the past 28 years and investigates whether the salinity change causing the change in vegetation cover. Landsat time series data of years 1985, 2000 and 2013 were used to generate Normalized Difference Vegetation Index (NDVI) and Soil Salinity Index (SI) images, which were then used in image differencing to identify vegetation and salinity change/no-change for two periods. Soil salinity during 2000–2013 exhibits much higher increase compared to 1985–2000, while the vegetation cover declined to 6.31% for the same period. Additionally, highly significant (p < 0.0001) negative relationships found between the NDVI and SI differencing images, confirmed the potential long-term linkage between the changes in soil salinity and vegetation cover. 相似文献
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3.
Amal Saidi Abdelfatah Tahiri Lahcen Ait Brahim Maraim Saidi 《Comptes Rendus Geoscience》2002,334(3):221-226
The fracturing analysis in the Permian basins of Jebilet and Rehamna (Hercynian Morocco) and the underlying terranes allowed us to suggest a model for their opening. Three tectonic episodes are distinguished: a transtensional episode NNE–SSW-trending (Permian I), occurring during the opening along sinistral wrench faults N70–110-trending, associated with synsedimentary normal faults; a transpressive episode ESE–WNW-trending (Permian II), initiating the closure, the normal faults playing back reverse faults and the N70 trending faults dextral wrench faults; a compressional episode NNW–SSE (post-Permian, ante-Triassic), accentuating the closure and the deformation and putting an end to the Tardi-Hercynian compressive movements. To cite this article: A. Saidi et al., C. R. Geoscience 334 (2002) 221–226. 相似文献
4.
A study on two closed salt lake basins, Tal Chapar and Parihara in the eastern margin of the Thar Desert, Rajasthan, was carried
out to unravel late Quaternary geomorphic evolution of these saline lakes. Both lakes are elliptical in shape bordered by
stabilised dunes, and are oriented in a NE-SW direction, i.e., in the direction of the prevailing summer monsoon wind. Both
lakes have been formed in the wind-shadow zones of isolated hills of Precambrian quartzite. Our study indicates that the late
Quaternary sediments in the lakes began with the cyclic deposition of laminated fine silt layers (0.5 m thick), rich in organic
matter, alternating with ripple cross-bedded sand layers (each ∼1.5–2 m thick). Sand layers that are moderately sorted are
separated by laminated silt-clay layers with gypsum/calcite and this unit occurs in the upper most 4 m sequence in deeper
sections. The presence of gypsum crystals within the laminated sediments suggests a high concentration of Ca in the inflowing
water.
At Parihara Lake the organic carbon-rich sediments at 95 cm depth was dated to 7,375 + 155/−150 year BP. At Tal Chapar radiocarbon
dates of 7,190 + 155/−150 and 9,903 + 360/−350 was obtained from the sediments rich in organic carbon occurring at a depth
of 1.35 m and 1.80 m, respectively. The study reveals strong hydrologic oscillations during the past ∼14,000 year BP (13,090 + 310/−300 year
BP).
Quaternary geomorphic processes, especially the strong aeolian processes during dry climatic phases, played a major role in
the formation of the lake basins, as well as the fringing linear dunes. Geochemical and mineralogical analyses of the lacustrine
sediments, supported by radiocarbon dates indicate the existence of an ephemeral lake earlier than ∼13,000 year BP as sediments
began to be deposited in a lacustrine environment implying sustained runoff in the catchments. A freshwater lake formed between
9,000 year and 7,000 year BP. The lake dried periodically and this strong fluctuating regime continued until about ∼7,000 year
BP. Mid-Holocene was wet and this was possibly due to higher winter rains A saline lake existed between 6,000 year and 1,300 year
BP and finally present day semi arid conditions set in since 1,200 year BP. Remnants of a habitation site (hearth and charred
bones) on stabilised dune at Devani near Tal Chapar were dated to 240 ± 120 year, while that at Gopalpura was dated to 335 ± 90 year.
These historical sites on stabilised dunes were, according to the local accounts, settlements of people who used the lake
brine for manufacturing salt. 相似文献
5.
The aeolian sedimentation record of the Thar desert 总被引：1，自引：0，他引：1
A review of the aeolian sedimentary record of the Thar desert is presented. This includes a regional survey of the major dune
forms, their genesis and their relationship to climate and other regional landforms. A key aspect of this work is the chronometry
of the dunes using luminescence methods. Luminescence dating of sand has enabled quantification of the duration of the phases
of sand aggradation and quiescence, time scales of dune migration and the dating of pedogenic carbonates. We demonstrate that
the conventional wisdom of synchronicity of dune aggradation with glacial epoch is not true in the context of Thar sands and
here only a short durationwindow of opportunity existed for dune aggradation. Luminescence ages further suggest that this window occurred during a transitional climatic
regime from glacial to interglacial about 4–10 ka after the glacial epoch. Other inferences included are that:
相似文献
| – | • the aeolian activity in the Thar began over > 150 ka, resolving that Thar is not of anthropogenic origin as suggested previously; |
| – | • the present spatial extent of the aeolian activity in the Thar is in a contracted stage compared to that in the geological past, which refutes the arguments on its rapid north-eastward expansion; |
| – | • the current dune migration rates in areas of significant human-induced disturbances are much higher than during the geological past; |
| – | • the monsoon activity in the Thar varied significantly, from being minimal during the isotopic marine stages 4 and 2 to being close to the present during stage 3; |
| – | • on shorter time scales the dune activities correlated with the lacustrine records of the region with a phase difference of a few centuries and a periodicity of ∼ 1500 years; |
| – | • the sand aggradation climate in the southern margin in Gujarat gradually shrank northwards such that in general dunes older than 10 ka are seen in the extreme southern margin and dunes younger than 2ka ages occur mostly in the western part of Rajasthan. |
6.
The Niger River is the third largest river in the African continent. Nine riparian countries share its basin, which rank all among the world’s thirty poorest. Existing challenges in West Africa, including endemic poverty, inadequate infrastructure and weak adaptive capacity to climate variability, make the region vulnerable to climate change. In this study, a risk-based methodology is introduced and demonstrated for the analysis of climate change impacts on planned infrastructure investments in water resources systems in the Upper and Middle Niger River Basin. The methodology focuses on identifying the vulnerability of the Basin’s socio-economic system to climate change, and subsequently assessing the likelihood of climate risks by using climate information from a multi-run, multi-GCM ensemble of climate projections. System vulnerabilities are analyzed in terms of performance metrics of hydroelectricity production, navigation, dry and rainy season irrigated agriculture, flooding in the Inner Delta of the Niger and the sustenance of environmental flows. The study reveals low to moderate risks in terms of stakeholder-defined threshold levels for most metrics in the 21st Century. The highest risk levels were observed for environmental flow targets. The findings indicate that the range of projected changes in an ensemble of CMIP3 GCM projections imply only relatively low risks of unacceptable climate change impacts on the present large-scale infrastructure investment plan for the Basin. 相似文献
7.
The present study was conducted to evaluate the effect of either individual or combined wheat bran(WB) replacement with Azolla pinnata supplemented with Digestin~(TM) in the diet of freshwater prawn, Macrobrachium rosenbergii Postlarvae(PL) on growth performance, nutrient utilization, chemical body composition and survival(%). Experimental diets were a wheat bran-soybean based diet with no Azolla and Digestin~(TM)(control, T_1), and diets containing 17% Azolla supplemented with Digestin~(TM) 0%(T_2), 1%(T_3), 2%(T_4) and 3%(T 5). Each experimental diet was allocated into three tanks(6 m~3/tank) fed for 12 wks. Each tank was subdivided into three equal pens by nets(2 m~3) and stoked with 84 PL/m~2. The experimental diets were readily consumed by prawns PLs where both high growth and good feed efficiency were achieved for all diets. The results showed that the diets containing A. pinnata supplemented with Digestin? at the level up to 3% have the higher growth and better nutrient utilization than the control diet. No differences were observed for moisture and protein content among the experimental diets. However, the highest protein content was observed on prawns fed on diets T_1 and T 5 respectively, while the lowest value was recorded for T_4 diet. The results also show that prawn PLs fed the diets contain A. pinnata and supplemented with Digestin~(TM) recorded the highest values of body lipid content compared to the control diet. Feed efficiency and economic conversion rate(ECR) values show that economic performance and the cost-effectiveness of the A. pinnata supplemented with up to 3% Digestin~(TM) recorded the highest net return, and therefore it is recommended for prawn, M. rosenbergii PL's. These results are clearly indicating that A. pinnata have a good potential for use in prawn diets at reasonable levels than other conventional diets. 相似文献
8.
Jerbi Hamza Sebai Amal Massuel Sylvain Riaux Jeanne Leduc Christian Tarhouni Jamila 《Hydrogeology Journal》2023,31(5):1181-1196
Long-term exploitation schemes in many regions are often based solely on hydrodynamic factors, while the agricultural use of groundwater undergoes significant changes over time. The Bouhefna-Haffouz aquifer system in central Tunisia is one of those cases where an aquifer exploitation scheme was well designed hydrodynamically to address the political needs at the time. Fifty years later, a numerical groundwater model has been conducted to assess the sustainability of the scheme. Results show that the scheme aimed to lower the groundwater level to reduce overflow to Merguellil Wadi and maintain it at a level that benefits agricultural profitability. This caused loss of the Merguellil baseflow, forcing farmers to switch from traditional irrigation canals to deep wells and motor pumps, thereby disrupting the hydrological budget even further. The numerical model indicates that the flow to the wadi reached zero in 1978, the average flow by vertical leakage decreased from 8 hm3 in 1970 to 2 hm3 in 2020, and the horizontal percolation between the regional aquifer units increased from 1 hm3 in 1970 to 6 hm3 in 2020. Although the groundwater exploitation scheme was not previously considered a factor in local hydrological changes, the results of this study demonstrate the significant impact of societal behavior following the scheme’s implementation on the hydrological budget of Merguellil Wadi.
相似文献9.
In this paper, we investigate the dynamics of Lemaitre-Tolman-Bondi spacetimes with imperfect fluid in the presence of electromagnetic field. We study the effects of charge with respect to an observer moving radially relative to the fluid, that is, a tilted observer. The relationship between various quantities in the tilted and non-tilted congruences is developed using the Einstein-Maxwell field equations. We explore various factors affecting the inhomogeneities in the energy density of the fluid and also discuss the stability of the non-tilted congruence. 相似文献
10.
We present a model which, for the first time, accounts for nucleation, growth and/or resorption of particles of variable composition in aqueous solutions (AS). Devised for describing the precipitation of binary solid solutions, it yields the time evolution of all ion activities in the AS, together with the particle population characteristics: number, size and composition profile of particles as a function of time and of their time of nucleation. We apply this numerical approach to the prototypical case of (Ba,Sr)CO3 solid solution precipitation. We demonstrate the great sensitivity of the composition profiles and particle sizes to the initial conditions under which the AS is prepared, and thus illustrate the possibility of engineering the particle characteristics into a chosen state. Finally, by comparing the precipitation of two solid solutions (Ba,Sr)CO3 and (Ba,Sr)SO4, we evidence the sensitivity of the particle composition profiles to the ratio of the end-member solubility products, which leads to the formation of core-shell particles in the case of (Ba,Sr)SO4. 相似文献