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Evaluation of the LISEM soil erosion model in two catchments in the East African Highlands 总被引:1,自引:0,他引:1
Under increasing population pressure, soil erosion has become a threat in the East African Highlands, and erosion modelling can be useful to quantify this threat. To test its applicability for this region, the LISEM soil erosion model was applied to two small catchments, one in the Usumbara Mountains, Tanzania, and the other on the slopes of Mount Kenya. Input data for the model were collected in both catchments, as were data on runoff and erosion that were used for calibration and validation of the model. LISEM was first calibrated on catchment outlet data, and afterwards simulated spatial patterns of erosion were compared to available erosion data. The results showed that LISEM can, after calibration, give good discharge predictions for some events, but not for all. However, LISEM generally overpredicted soil loss from the catchments. Comparison with observed erosion patterns did not show overprediction, but according to the model, erosion was more widespread than was observed. There are several reasons for these discrepancies. First, it is difficult to obtain enough accurate data to run the model, such as accurate maps, rainfall data and soil and plant characteristics. Second, it is also difficult to obtain accurate data to evaluate the performance of the model, either for the catchment outlet or spatially, therefore observed erosion rates are also uncertain. Third, the model could not deal correctly with complex events, i.e. those having double rainfall peaks, and might also have difficulties with catchment characteristics such as soil type and the complexity of land use. Finally, LISEM could not deal with events in which throughflow or baseflow played a role, which was to be expected since those processes are not simulated by LISEM. Nevertheless, LISEM could be calibrated to give good discharge predictions for some events, and also gave reasonable results when compared to data obtained from erosion plots. Furthermore, only complex, distributed, storm‐based models such as LISEM can give spatial predictions for single storms. Therefore, it is concluded that if the aim is spatial prediction on an event basis, there is no alternative to complex erosion models such as LISEM, but if the aim is to predict average annual erosion, the data‐demanding, physically based LISEM erosion model may not be the most appropriate model. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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J. M. Liotard J. M. Dautria D. Bosch M. Condomines H. Mehdizadeh J.-F. Ritz 《International Journal of Earth Sciences》2008,97(1):89-102
The activity of the Damavand volcano (Central Alborz, northern Iran) began 1.8 Ma ago and continued up to 7 ka BP. Although
the volcanic suite is clearly of shoshonitic affinity, only two petrographic types can be distinguished in the studied lavas:
(1) weakly differentiated absarokites (49 < %SiO2 < 51), scattered around the volcano but with a regional extension, (2) highly differentiated banakites (59 < %SiO2 < 63), which form the bulk of the 4,000 m thick volcanic pile. All lavas are alkalic (3.7 < %K2O < 5), REE and LILE-rich (e.g., 85 < La < 148 ppm; 9 < Th < 32 ppm) and show highly fractionated REE patterns (69 < La/Yb < 115)
and pronounced Nb–Ta negative anomalies. The absarokites are characterised by Sr (0.7045–0.7046) and Nd (0.51266–0.51269)
isotope compositions close to the Bulk Earth values, and distinct from those of the banakites (0.7047 < 87Sr/86Sr < 0.7049, 0.51258 < 143Nd/144Nd < 0.51262). The Pb isotope ratios are also slightly lower in the absarokites than in the banakites (18.71 < 206Pb/204Pb < 18.77, 15.62 < 207Pb/204Pb < 15.63, 38.85 < 208Pb/204Pb < 38.91, and 18.77 < 206Pb/204Pb < 18.84, 15.62 < 207Pb/204Pb < 15.64, 38.94 < 208Pb/204Pb < 39.06, respectively). Overall, there is a clear tendency towards higher Sr, Pb and lower Nd isotope ratios with increasing
degree of differentiation. This study suggests that the absarokites result from a low degree of partial melting (∼5%) of a
highly metasomatized mantle source, which inherited its characteristics from an old subduction setting. The initiation of
volcanic activity 1.8 Ma ago results from variations in the lithospheric thermal regime, probably related to lithospheric
delamination as proposed for Anatolia (Pearce et al. 1990). The banakites are mainly generated by extensive fractional crystallisation (∼70%) of the absarokitic magma, with a limited
amount (a few percents) of assimilation of an old crustal component, in the form of bulk assimilation or AFC processes, which
both can explain the Sr, Nd and Pb isotope data. 相似文献
56.
P. Wernert K. Schulmann F. Chopin P. Štípská D. Bosch M. El Houicha 《Journal of Metamorphic Geology》2016,34(9):917-940
New petrographic and microstructural observations, mineral equilibria modelling and U/Pb (monazite) geochronological studies were carried out to investigate the relationships between deformation and metamorphism across the Rehamna massif (Moroccan Variscan belt). In this area, typical Barrovian (muscovite to staurolite) zones developed in Cambrian to Carboniferous metasedimentary rocks that are distributed around a dome‐like structure. First assemblages are characterized by the presence of locally preserved andalusite, followed by prograde evolution culminating at 6 kbar and 620 °C in the structurally deepest staurolite zone rocks. This Barrovian sequence was subsequently uplifted to supracrustal levels, heterogeneously reworked at greenschist facies conditions, which was followed locally by static growth of andalusite, indicating heating to 2.5–4 kbar and 530–570 °C. The 206Pb/238U monazite age of 298.3 ± 4.1 Ma is interpreted as minimum age of peak metamorphic conditions, whereas the ages of 275.8 ± 1.7 Ma and 277.0 ± 1.1 Ma date decompression and heating at low pressure, in agreement with previous dating of Permian granitoids intruding the Rehamna massif. The prograde metamorphism occurred during thickening and associated horizontal flow in the deeper crust (S1 horizontal schistosity). The horizontally disposed metamorphic zones were subsequently uplifted by a regional scale antiform during ongoing N–S compression. The re‐heating of the massif follows late massive E–W shortening, refolding and retrograde shearing of all previous fabrics coevally with regionally important intrusions of Permian granitoids. We argue that metamorphic evolution of the Rehamna massif occurred several hundred kilometres from the convergent plate boundaries in the interior of continental Gondwanan plate. The tectonometamorphic history of the Rehamna massif is put into Palaeozoic plate tectonic perspective and Late Carboniferous reactivation of (Devonian)–Early Carboniferous basins formed during stretching of the north Gondwana margin and formation of the Palaeotethys Ocean. The inherited heat budget of these magma‐rich basins plays a role in the preferential location of this intracontinental orogen. It is shown that rapid transition from lithospheric stretching to compression is characterized by specific HT type of Barrovian metamorphism, which markedly differs from similar Barrovian sequences along Palaeozoic plate boundaries reported from Variscan Europe. 相似文献
57.
Surhud More † Frank C. van den Bosch Marcello Cacciato H. J. Mo Xiaohu Yang Ran Li 《Monthly notices of the Royal Astronomical Society》2009,392(2):801-816
The kinematics of satellite galaxies reflect the masses of the extended dark matter haloes in which they orbit, and thus shed light on the mass–luminosity relation (MLR) of their corresponding central galaxies. In this paper, we select a large sample of centrals and satellites from the Sloan Digital Sky Survey and measure the kinematics (velocity dispersions) of the satellite galaxies as a function of the r -band luminosity of the central galaxies. Using the analytical framework presented in More, van den Bosch & Cacciato, we use these data to infer both the mean and the scatter of the MLR of central galaxies, carefully taking account of selection effects and biases introduced by the stacking procedure. As expected, brighter centrals on average reside in more massive haloes. In addition, we find that the scatter in halo masses for centrals of a given luminosity, σlog M , also increases with increasing luminosity. As we demonstrate, this is consistent with σlog L , which reflects the scatter in the conditional probability function P ( L c | M ) , being independent of halo mass. Our analysis of the satellite kinematics yields σlog L = 0.16 ± 0.04 , in excellent agreement with constraints from clustering and group catalogues, and with predictions from a semi-analytical model of galaxy formation. We thus conclude that the amount of stochasticity in galaxy formation, which is characterized by σlog L , is well constrained, independent of halo mass and in a good agreement with current models of galaxy formation. 相似文献
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Cecilia Scorza & Frank C. van den Bosch 《Monthly notices of the Royal Astronomical Society》1998,300(2):469-478
Hubble Space Telescope images of two early-type galaxies harbouring both nuclear and outer stellar discs are studied in detail. By means of a photometric decomposition, the images of NGC 4342 and 4570 are analysed and the photometric properties of the nuclear discs investigated. We find a continuity of properties in the parameter space defined by the central surface brightness μ0 and the scalelength R d of discs in spirals, S0s and embedded discs in ellipticals, in the sense that the nuclear discs extend the observed disc properties even further towards smaller scalelengths and brighter central surface brightnesses. When including the nuclear discs, disc properties span more than four orders of magnitude in both scalelength and central surface brightness. The nuclear discs studied here are the smallest and brightest stellar discs known, and as such, they are as extreme in their photometric properties as Malin I, when compared with typical galactic discs that obey Freeman's law. We discuss a possible formation scenario in which the double-disc structure observed in these galaxies has been shaped by now dissolved bars. Based on the fact that the black holes known to exist in some of these galaxies have masses comparable to those of the nuclear discs, we explore a possible link between the black holes and the nuclear discs. 相似文献
60.
Mehdi Mechati Dalila Hammor Delphine Bosch Olivier Bruguier Laure Fernandez 《International Geology Review》2018,60(4):464-478
Metagabbros and amphibolites exposed in the Bou-Maïza area of the Edough massif (northeast Algeria) are described in detail. Field and petro-structural observations point to the syn-sedimentary emplacement of gabbros as clasts, blocks and lenses of polymictic gabbroic breccias. Associated amphibolites display fine-scale parallel sedimentary bedding and represent mafic epiclastites, litharenites and mafic greywackes. The mafic beds and lenses are intercalated with aluminous pelitic schists of continental origin, quartzite and marble. It is concluded that all mafic rocks from this locality derive from the erosion of an oceanic plutono-volcanic complex of MORB affinity that was reworked in a block matrix mélange and emplaced as turbidites and debris flows during the Mesozoic. We propose a convergent plate margin setting for these formations connected with the subducted Calabrian branch of the Tethyan slab. 相似文献