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121.
Climate change is expected to increase temperatures and lower rainfall in Mediterranean regions; however, there is a great degree of uncertainty as to the amount of change. This limits the prediction capacity of models to quantify impacts on water resources, vegetation productivity and erosion. This work circumvents this problem by analysing the sensitivity of these variables to varying degrees of temperature change (increased by up to 6·4 °C), rainfall (reduced by up to 40%) and atmospheric CO2 concentrations (increased by up to 100%). The SWAT watershed model was applied to 18 large watersheds in two contrasting regions of Portugal, one humid and one semi‐arid; incremental changes to climate variables were simulated using a stochastic weather generator. The main results indicate that water runoff, particularly subsurface runoff, is highly sensitive to these climate change trends (down by 80%). The biomass growth of most species showed a declining trend (wheat down by 40%), due to the negative impacts of increasing temperatures, dampened by higher CO2 concentrations. Mediterranean species, however, showed a positive response to milder degrees of climate change. Changes to erosion depended on the interactions between the decline in surface runoff (driving erosion rates downward) and biomass growth (driving erosion rates upward). For the milder rainfall changes, soil erosion showed a significant increasing trend in wheat fields (up to 150% in the humid watersheds), well above the recovery capacity of the soil. Overall, the results indicate a shift of the humid watersheds to acquire semi‐arid characteristics, such as more irregular river flows and increasingly marginal conditions for agricultural production. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
122.
Vanessa Cerqueira Koppe João Felipe Coimbra Leite Costa Jair Carlos Koppe Fernando Gambin Gary Fallon Nick Davies 《Natural Resources Research》2007,16(4):293-303
Seismic reflection methods measure the time a seismic wave takes to travel through the ground, from the user defined source
to a series of signal monitoring sensors known as geophones. The measured times need to be depth converted to allow for integration
with other geological data. In order to convert from time to depth, an estimate of the rock volume velocity field must be
made. The velocity field estimate can be made by assignment of velocity estimates to a geological model independent of the
seismic processing. This article presents the results of using the acoustic geophysical log data extrapolated via sequential
Gaussian simulation to derive the velocity field. The uncertainties associated with the velocity estimates were significant
and provided the means to assess confidence limits for the actual depth determination. The technique is assessed by application
to a major coal deposit, approximately 2.1 m thick and 210 m deep. Considering only the uncertainty associated with estimating
the velocity field, half of the confidence interval values showed approximately 1 m of uncertainty in depth. The application
of sequential Gaussian simulation to model the 3D distribution of acoustic velocity can be extended to other geophysical log
parameters or derived estimates. 相似文献
123.
Adakitic magmas in the Ecuadorian Volcanic Front: Petrogenesis of the Iliniza Volcanic Complex (Ecuador) 总被引:1,自引:0,他引:1
Silvana Hidalgo Michel Monzier Hervé Martin Gilles Chazot Jean-Philippe Eissen Jo Cotten 《Journal of Volcanology and Geothermal Research》2007
The Iliniza Volcanic Complex (IVC) is a poorly known volcanic complex located 60 km SSW of Quito in the Western Cordillera of Ecuador. It comprises twin peaks, North Iliniza and South Iliniza, and two satellite domes, Pilongo and Tishigcuchi. The study of the IVC was undertaken in order to better constrain the role of adakitic magmas in the Ecuadorian arc evolution. The presence of volcanic rocks with an adakitic imprint or even pristine adakites in the Ecuadorian volcanic arc is known since the late 1990s. Adakitic magmas are produced by the partial melting of a basaltic source leaving a garnet rich residue. This process can be related to the melting of an overthickened crust or a subducting oceanic crust. For the last case a special geodynamic context is required, like the subduction of a young lithosphere or when the subduction angle is not very steep; both cases are possible in Ecuador. The products of the IVC, made up of medium-K basaltic andesites, andesites and dacites, have been divided in different geochemical series whose origin requires various interactions between the different magma sources involved in this subduction zone. North Iliniza is a classic calc-alkaline series that we interpret as resulting from the partial melting of the mantle wedge. For South Iliniza, a simple evolution with fractional crystallization of amphibole, plagioclase, clinopyroxene, magnetite, apatite and zircon from a parental magma, being itself the product of the mixing of 36% adakitic and 64% calc-alkaline magma, has been quantified. For the Santa Rosa rhyolites, a slab melting origin with little mantle interactions during the ascent of magmas has been established. The Pilongo series magma is the product of a moderate to high degree (26%) of partial melting of the subducting oceanic crust, which reached the surface without interaction with the mantle wedge. The Tishigcuchi series shows two stages of evolution: (1) metasomatism of the mantle wedge peridotite by slab melts, and (2) partial melting (10%) of this metasomatized source. Therefore, the relative ages of the edifices show a geochemical evolution from calc-alkaline to adakitic magmas, as is observed for several volcanoes of the Ecuadorian arc. 相似文献
124.
Danièle Valdes Jean-Paul Dupont Nicolas Massei Benoît Laignel Joël Rodet 《Comptes Rendus Geoscience》2005,337(15):1365-1374
In karst systems, rain events often result in a decrease of the conductivity (a tracer of dissolved phase transport) and an increase in turbidity (a tracer of suspended solids transport) at wells and springs. This study shows that the comparison of suspended solids and solute transport by the coupled approach of curves (Turbidity–Conductivity) and autocorrelations gives evidence of the transport processes in the karst network and allows understanding the karst hydrodynamics. To cite this article: D. Valdes et al., C. R. Geoscience 337 (2005). 相似文献
125.
da Rosa CE de Souza MS Yunes JS Proença LA Nery LE Monserrat JM 《Marine pollution bulletin》2005,50(9):956-964
In January of 2003, a cyanobacterial bloom in the Patos' Lagoon (Southern Brazil) (32 degrees 05'S-52 degrees 12'W) was observed. Water samples were taken to identify the composition and abundance of the bloom, as well as the occurrence of toxins. The effects of this occurrence on the estuarine worm Laeonereis acuta (Polychaeta, Nereididae) was also evaluated. Predominance of cyanobacteria, particularly Anabaena trichomes ( approximately 2.5.10(6) individuals per liter) was observed, and low concentrations of microcystins and anticholinesterasic toxins were detected. Augmented levels of lipid hydroperoxides (LPO) and glutathione-S-transferase activity, and lowering of total protein content were also observed in organisms collected during the bloom event. Although non-toxic, the cyanobacterial bloom could augment the cycle of hyper-oxygenation and hypoxia in the water. During hyperoxia, L. acuta, an oxyconformer, should consume more oxygen, thus augmenting the rate of reactive oxygen species generation. A repeated cycle of hyper-oxygenation and hypoxia would finally induce oxidative stress, as evidenced by the high levels of LPO and glutathione-S-transferase activity. 相似文献
126.
Fabien Arnaud Joël Serralongue Thierry Winiarski Marc Desmet Martine Paterne 《Comptes Rendus Geoscience》2006,338(4):244-252
In Lake Anterne (NW French Alps), the Roman period is characterised by a lead contamination more important than that of the 1970s, due to the use of leaded gasoline. The maximum of this contamination period has been varve-dated 220 AD, i.e., during the optimum of Roman civilization in the Alps. Crossing palaeoenvironmental and archaeological evidences points out the economic importance of the town of Passy for the City of Vienne and yields a new example of lead contamination due to local metallurgical activity rather than distant impact of the exploitation of the Spanish Rio Tinto mine. To cite this article: F. Arnaud et al., C. R. Geoscience 338 (2005). 相似文献
127.
Jo Moore Andreas Beinlich Jennifer K. Porter Cristina Talavera Jasper Berndt Sandra Piazolo Håkon Austrheim Andrew Putnis 《Journal of Metamorphic Geology》2020,38(1):103-127
As a common constituent of metamorphic assemblages, rutile provides constraints on the timing and conditions of rock transformation at high resolution. However, very little is known about the links between trace element mobility and rutile microstructures that result from synmetamorphic deformation. To address this issue, here we combine in situ LA-ICP-MS and sensitive high-resolution ion microprobe trace element data with electron back-scatter diffraction microstructural analyses to investigate the links between rutile lattice distortions and Zr and U–Pb systematics. Furthermore, we apply this integrated approach to constrain further the temperature and timing of amphibolite facies metamorphism and deformation in the Bergen Arcs of southwestern Norway. In outcrop, the formation of porphyroblastic rutile in dynamically hydrated leucocratic domains of otherwise rutile-poor statically hydrated amphibolite provides key contextual information on both the ambient conditions of hydration and deformation and the composition of the reactive fluid. Rutile in amphibolite recorded ambient metamorphic temperatures of ~590–730°C during static hydration of the granulitic precursor. By contrast, rutile from leucocratic domains in the directly adjacent shear zone indicates that deformation was accompanied by a localized increase in temperature. These higher temperatures are recorded in strain-free rutile (~600–860°C) and by Zr concentration measurements on low-angle boundaries and shear bands (620–820°C). In addition, we also observe slight depletions of Zr and U along rutile low-angle boundaries relative to strain-free areas in deformed grains from the shear zone. This indicates that crystal–plastic deformation facilitated the compositional re-equilibration of rutile upon cooling to slightly below the peak temperature of deformation. Cessation of deformation at mid-crustal conditions near ~600°C is recorded by late stage growth of small (<150 µm) rutile in the high-strain zones. U–Pb age data obtained from the strain-free and distorted rutile grains cluster in distinct populations of 437.4 ± 2.7 Ma and c. 405–410 Ma, respectively. These different ages are interpreted to reflect the difference in closure for thermally induced Pb diffusion between undeformed and deformed rutile during post-deformation exhumation and cooling. Thus, our results provide a reconstruction of the thermochronological history of the amphibolite facies rocks of the Lindås Nappe and highlight the importance of integration of microstructural data during application of thermometers and geochronometers. 相似文献
128.
Pereira Rafael H. M. Andrade Pedro R. Vieira João Pedro Bazzo 《Journal of Geographical Systems》2023,25(3):453-466
Journal of Geographical Systems - The creation of the General Transit Feed Specification (GTFS) in the mid-2000s provided a new data format for cities to organize and share digital information on... 相似文献
129.
Libório Matheus Pereira de Abreu João Francisco Ekel Petr Iakovlevitch Machado Alexei Manso Correa 《Journal of Geographical Systems》2023,25(2):185-211
Journal of Geographical Systems - The weighting of sub-indicators is widely debated in the composite indicator literature. However, these weighting schemes’ effects on the composite... 相似文献
130.
José Maria Santos Luís Reino João Oliveira Paulo Pinheiro Pedro Raposo Almeida Rui Cortes Maria Teresa Ferreira 《Aquatic Sciences - Research Across Boundaries》2011,73(2):233-245
Knowledge of the distribution of species life stages at multiple spatial scales is fundamental to both a proper assessment
of species management and conservation programmes and the ability to predict the consequences of human disturbances for river
systems. The habitat requirements of three native cyprinid species—the Iberian barbel Barbus bocagei Steindachner, the Iberian straight-mouth nase Pseudochondrostoma polylepis (Steindachner), and the Northern straight-mouth nase Pseudochondrostoma duriense (Coelho)—were examined at 174 undisturbed or minimally disturbed sites in 8 river catchments across western Iberia, by modelling
occurrence and counts of species life stages at two spatial scales—large (regional) and instream (local)—using hurdle models.
All the life stages of the barbel showed a negative association with upstream high-gradient river reaches, whereas juvenile
P. duriense favoured such areas. Stream width and openness were negatively related with the occurrence of juvenile and small adult barbel,
but not with large adults. Juvenile nase, on the other hand, were found to be mainly confined to fast-flowing habitats with
high instream cover and coarser substrata. Advanced life stages of the barbel were mainly associated with the “pure” regional
and shared components, whereas the purely local attributes accounted for much of the model variation among nases, in particular
juveniles, and juvenile barbel. The results of this study are useful for setting or refining management goals, and highlight
the need to separately consider life stages when performing conservation-related studies of species distribution. 相似文献