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41.
Simulation of soil erosion and deposition in a changing land use: A modelling approach to implement the support practice factor 总被引：1，自引：0，他引：1
Using the USPED (Unit Stream Power Erosion Deposition) model, three land use scenarios were analysed for an Italian small catchment (15 km2) of high landscape value. The upper Orme stream catchment, located in the Chianti area, 30 km south of Florence, has a long historical agriculture record. Information on land use and soil conservation practices date back to 1821, hence offering an opportunity to model impacts of land use change on erosion and deposition. For this study, a procedure that takes into account soil conservation practices and potential sediment storage is proposed. The approach was to calculate and model the flow accumulation considering rural and logging roads, location of urban areas, drainage ditches, streams, gullies and permanent sediment sinks. This calculation attempts to assess the spatial variability, especially the impact of support practices (P factor). Weather data from 1980–2003 were taken into account to calculate the R factor. However, to consider the intense pluviometric conditions in terms of the erosivity factor, the 0.75th quantile was used, while the lowest erosivity was modelled using the 0.25th quantile. Results of the USPED model simulation show that in 1821 the mean annual net erosion for the watershed was 2.8 Mg ha− 1 y− 1; in 1954 it was 4.2 Mg ha− 1 y− 1; and in 2004 it was 5.3 Mg ha− 1 y− 1. Conservation practices can reduce erosion processes by ≥ 20 Mg ha− 1 y− 1 when the 1821 practices are introduced in the present management. On the other hand, if the support practices are not considered in the model, soil erosion risk is overestimated. Field observation for the present-day simulation confirmed that erosion and associated sediment deposition predicted by the model depend, as expected, on geomorphology and land use. The model shows limitations that are mainly due to the input data. A high resolution DEM is essential for the delineation of reliable topographic potential to predict erosion and deposition especially in vineyards. 相似文献
42.
Dipankar Chakraborti Mohammad Mahmudur Rahman Bhaskar Das Amit Chatterjee Dipankar Das Biswajit Nayak Arup Pal Uttam Kumar Chowdhury Sad Ahmed Bhajan Kumar Biswas Mrinal Kumar Sengupta Md. Amir Hossain Gautam Samanta M. M. Roy Rathindra Nath Dutta Khitish Chandra Saha Subhas Chandra Mukherjee Shyamapada Pati Probir Bijoy Kar Adreesh Mukherjee Manoj Kumar 《Hydrogeology Journal》2017,25(4):1165-1181
During a 28-year field survey in India (1988–2016), groundwater arsenic contamination and its health effects were registered in the states of West Bengal, Jharkhand, Bihar and Uttar Pradesh in the Ganga River flood plain, and the states of Assam and Manipur in the flood plain of Brahamaputra and Imphal rivers. Groundwater of Rajnandgaon village in Chhattisgarh state, which is not in a flood plain, is also arsenic contaminated. More than 170,000 tubewell water samples from the affected states were analyzed and half of the samples had arsenic >10 μg/L (maximum concentration 3,700 μg/L). Chronic exposure to arsenic through drinking water causes various health problems, like dermal, neurological, reproductive and pregnancy effects, cardiovascular effects, diabetes mellitus, diseases of the respiratory and gastrointestinal systems, and cancers, typically involving the skin, lungs, liver, bladder, etc. About 4.5% of the 8,000 children from arsenic-affected villages of affected states were registered with mild to moderate arsenical skin lesions. In the preliminary survey, more than 10,000 patients were registered with different types of arsenic-related signs and symptoms, out of more than 100,000 people screened from affected states. Elevated levels of arsenic were also found in biological samples (urine, hair, nails) of the people living in affected states. The study reveals that the population who had severe arsenical skin lesions may suffer from multiple Bowens/cancers in the long term. Some unusual symptoms, such as burning sensation, skin itching and watering of eyes in the presence of sun light, were also noticed in arsenicosis patients. 相似文献
43.
In Belgium, IWVA uses managed aquifer recharge (MAR) to recharge the aquifer with treated wastewater generated from the communities to sustain the potable water supply on the Belgian coast. This MAR facility is faced with a challenge of reduced infiltration rates during the winter season when pond water temperatures near 4°C. This study involves the identification of the predominant factor influencing the rate of infiltration through the pond bed. Several factors, including pumping rates, natural recharge, tidal influences of the North Sea and pond-water temperature, were identified as potential causes for variation of the recharge rate. Correlation statistics and linear regression analysis were used to determine the sensitivity of the infiltration rate to the aforementioned factors. Two groundwater flow models were developed in visual MODFLOW to simulate the water movement under the pond bed and to obtain the differences in flux to track the effects of variation of hydraulic conductivity during the two seasons. A 32% reduction in vertical hydraulic gradient in the top portion of the aquifer was observed in winter, causing the recharge rates to fluctuate. Results showed that water temperature caused a 30% increase in hydraulic conductivity in summer as compared with winter and has the maximum impact on infiltration rate. Cyclic variations in water viscosity, occurring because of seasonal temperature changes, influence the saturated hydraulic conductivity of the pond bed. Results from the models confirm the impact on infiltration rate by temperature-influenced hydraulic conductivity. 相似文献
44.
Pradip Samanta Soumik Mukhopadhyay Anudeb Mondal Subir Sarkar 《Journal of Asian Earth Sciences》2011,40(2):542-549
Ubiquitous microorganisms, especially cyanobacteria preferably grow on the sediment surface thereby producing microbial mats. In the absence of grazers and bioturbators, microbial mat is a unique feature of the Proterozoic. Most of the papers so far published described a wide variety of bed surface microbial mat structures with rare illustrations from sections perpendicular to bedding. Nonetheless, bed surface exposures are relatively rare in rock records. This limitation of bed surface exposures in rock records suggest that a study of microbial mats in bed-across sections is needed. The 60 m thick coastal marine interval of the Sonia Sandstone Formation is bounded between two terrestrial intervals, a transgressive lag at the base and an unconformity at the top, and has been chosen for exploration of microbial mat structures in bed-across sections. A wide variety of microbial mat-induced structures in bed-across sections are preserved within the coastal interval of the Sonia Sandstone. Though many of these structures are similar in some aspects with bed surface structures, some of those presented here are new. The palaeogeographic range of these microbial structures extends from supralittoral to neritic. Diagenetic alterations of microbial mats produce pyrite and those zones are suitable for the preservation of microbial remains. SEM and EDAX analyses show fossil preservation of filamentous microbial remains that confirm the presence of microbial mats within the coastal interval of the Sonia Sandstone. Effects of proliferation of microbial mats in the siliciclastic depositional setting are numerous. The mat-cover on sediment surfaces hinders reworking and/or erosion of the sediments thereby increases the net sedimentation rate. Successive deposition and preservation of thick microbial mat layer under reducing environments should have a great potential for hydrocarbon production and preservation and therefore these Proterozoic formations could be a target for exploration. 相似文献
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46.
In high-grade (granulite facies) quartzofeldspathic rocks the progressive development of a fabric records contrasting deformation
behaviour of quartz and feldspar. Feldspar has undergone deformation mainly by recrystallization-accommodated dislocation
creep and produced smaller recrystallized grains progressively in the course of deformation. Quartz has not deformed solely
by dislocation creep but also by a diffusion-controlled mechanism. Dislocation climb is important in the dislocation creep
of quartz. In contrast to feldspar, quartz grains have not recrystallized into smaller grains at any stage of deformation.
Rather, they have transformed initially to short monocrystalline ribbons and ultimately to long polycrystalline ribbons. This
textural change of quartz is a continuous process and has taken place in the course of bulk textural change of the rocks during
the deformation. 相似文献
47.
D S Mackay S Samanta D E Ahl B E Ewers S T Gower & S N Burrows 《Transactions in GIS》2003,7(1):139-153
All land surface process models require parameters that are proxies for spatial processes that are impractical or impossible to measure. Recent developments in model parameter estimation theory suggest that information obtained from calibrating such models is inherently uncertain in nature. As a consequence, identification of optimum parameter values is often highly non–specific. A calibration framework using fuzzy logic is presented to deal with such uncertain information. An application of this technique to calibrate the sub–canopy controls on transpiration in a land surface process model demonstrates that objective estimates of parameter values and expected ranges of predictions can be obtained with suitable choices for objective functions. An iterative refinement in parameter estimates was possible with conditional sampling techniques. The automated approach was able to correctly identify parameter tradeoffs such that two strongly different sets of parameters could 相似文献
48.
Basanta Kumar Samanta 《Pure and Applied Geophysics》1966,63(1):68-81
Summary A direct method has been applied in this paper to find the stresses in some steadily rotating, self-gravitating spherical earth models. 相似文献
49.
Natural Hazards - The present paper assesses the slope stability of the Tungnath Temple at Rudraprayag District, in the Indian state of Uttarakhand, and suggests the remedial measures. The... 相似文献
50.
J. K. Ghosh J. Bhanja S. Purkayastha T. Samanta S. Sengupta 《Mathematical Geology》2002,34(5):505-528
A geological map is the representation, on a two-dimensional plane, of the disposition of three-dimensional rock bodies exposed on the earth's surface. The problem of mapping is essentially that of dividing an area into homogeneous subregions on the basis of the exposed rock types. Automatic Bayesian methods of model selection using default Bayes factors have been employed to solve the problem of choosing a set of boundaries between homogeneous subregions, assuming no complication excepting low-angle tilting affected rock bodies. The method is tested on two data sets. A sampling scheme for optimum allocation of observation points is also presented. 相似文献