ABSTRACTThis work examines 140 hydrological studies conducted in the Mediterranean region. It identifies key characteristics of the hydrological responses of Mediterranean catchments at various time scales and compares different methods and modelling approaches used for individual-catchment studies. The study area is divided into the northwestern (NWM), eastern (EM) and southern (SM) Mediterranean. The analysis indicates regional discrepancies in which the NWM shows the most extreme rainfall regime. A tendency for reduced water resources driven by both anthropogenic and climatic pressures and a more extreme rainfall regime are also noticeable. Catchments show very heterogeneous responses over time and space, resulting in limitations in hydrological modelling and large uncertainties in predictions. However, few models have been developed to address these issues. Additional studies are necessary to improve the knowledge of Mediterranean hydrological features and to account for regional specificities.
Editor D. Koutsoyiannis Associate editor A. Efstratiadis 相似文献
The south Solaf zone in SW Sinai comprises a metasedimentary sequence of metagraywackes intercalated with minor metavolcanic sheets, metasiltstones, meta-arenites, and calc–silicates. The metavolcanics (basalt–andesite) show high- to medium-K calc–alkaline nature. They exhibit distinctive Nb-Ta negative anomalies relative to enriched LILE, being highly similar to active continental margin lavas, but they also have the characteristics of rift-related magmatism. Magmas of similar composition are interpreted to be formed in an extensional environment and their source regions are zones of enriched subcontinental lithosphere. The metasediments are poor to moderate sorting, intercalated to the north with minor impure calcareous layers. Geochemical investigation shows that they are immature to semi-mature sediments derived from a source of mafic to felsic composition. These metasediments are chemically similar to the active continental margins and are comparable to the Feiran gneisses and metagraywackes that were deposited before 800 Ma in an extensional environment. The investigated rocks suffered LP-HT amphibolite facies metamorphism. The P-T estimates using various thermobarometric calibrations gave temperatures of 554–610 °C and pressures of 2.2–4.0 kbar. 相似文献
his study presents the first and detail field investigations of exposed deposits at proximal sections of the Barombi Mbo Maar (BMM), NE Mt Cameroon, with the aim of documenting its past activity, providing insight on the stratigraphic distribution, depositional process, and evolution of the eruptive sequences during its formation. Field evidence reveals that the BMM deposit is about 126m thick, of which about 20m is buried lowermost under the lake level and covered by vegetation. Based on variation in pyroclastic facies within the deposit, it can be divided into three main stratigraphic units: U1, U2 and U3. Interpretation of these features indicates that U1 consists of alternating lapilli-ash-lapilli beds series, in which fallout derived individual lapilli-rich beds are demarcated by surges deposits made up of thin, fine-grained and consolidated ash-beds that are well-defined, well-sorted and laterally continuous in outcrop scale. U2, a pyroclastic fall-derived unit, shows crudely lenticular stratified scoriaceous layers, in which many fluidal and spindle bombs-rich lapilli-beds are separated by very thin, coarse-vesiculatedash-beds, overlain by a mantle xenolith- and accidental lithic-rich explosive breccia, and massive lapilli tuff and lapillistone. U3 displays a series of surges and pyroclastic fall layers. Emplacement processes were largely controlled by fallout deposition and turbulent diluted pyroclastic density currents under “dry” and “wet” conditions. The eruptive activity evolved in a series of initial phreatic eruptions, which gradually became phreatomagmatic, followed by a phreato-Strombolian and a violent phreatomagmatic fragmentation. A relatively long-time break, demonstrated by a paleosol between U2 and U3, would have permitted the feeding of the root zone or the prominent crater by the water that sustained the next eruptive episode, dominated by subsequent phreatomagmatic eruptions. These preliminary results require complementary studies, such as geochemistry, for a better understanding of the changes in the eruptive styles, and to develop more constraints on the maar’s polygenetic origin. 相似文献
The distribution of phytoplankton abundance, biomass and species composition coupled with environmental factors and metazooplankton was studied relatively intensively and over a period of four consecutive years in five ponds featuring a gradient of increasing salinity from near to that of sea water to a nine-fold concentration from 2000 to 2003. The results indicate that the physical characteristics of the water (temperature and salinity) were quite similar over the years. Nutrients, which were concentrated in pond A1, decreased with increases in salt concentration. The composition of the phytoplankton community showed strong seasonality. Diatoms dominated in the first ponds A1, A16 and C2-1, followed by dinoflagellates. Chlorophyceae dominated the phytoplankton community in the hypersaline ponds M2 and TS. Cyanobacteriae were relatively abundant in ponds M2 and TS. The highest phytoplankton density and biomass were found in the ponds with the highest salinity due to the proliferation of Dunaliella salina (Chlorophyta: Volvocales). The inter-annual study of phytoplankton succession in the Sfax solar salterns showed slight differences among the years of study due to the stability of the environmental conditions. Phytoplankton communities were permanently primitive, stage 1 – structured as they failed to build complexity because of salt stress which operates for longer and above any other variables. This reduced frequency of disturbance to the existing course of regulation, allowed the community to “mature” from its “primitive” state, rather than experience frequent structural setbacks. 相似文献
The Ouarsenis area is one of the most developed karstic systems of Algeria. It is a karst reservoir drinking water with a population of more than 50,000 people taking fully benefit from it. To understand the development of this karstic system, the local tectonic history of the four main mountain ranges of this culminating area (Ouarsenis) has been analyzed. Although previously identified primarily Cenozoic tectonic activities have been observed, a set of NW-SE joints intersecting the Jurassic limestone has been associated to a post-nappes tectonic events. Moreover, numerous joint sets oriented NNE/SSW have been identified almost over the entire culminating area. These joints are the direct consequence of the following stress history: (i) a NW/SE shortening responsible for a major overlap and the first fold (P1) phase, (ii) a second NNE/SSW shortening stage responsible for the second folding (P2) phase associated with 70° N sinistral strike-slip trend, (iii) a WNW/ESE extension phase resulting from the change of σ3 stress vertical axis, and (iv) a shearing stress creating a 120° N sinistral strike-slip fault. Only the late phases are responsible of the development of joints, which have been karstified later on. Indeed, significant families of karstified joints, i.e., 20° and 70° N have been found. These joints are related to the extensional and shearing modes, respectively, and linked to a particular in situ karstogenesis. Moreover, this study suggests an ancient establishment of the karstic systems in the Ouarsenis region in at least two stages: pre-figured and activated behaviors during the Cenozoic. 相似文献
The Mio-Pliocene aquifer of the coastal sedimentary basin of Benin is the most exploited aquifer for water supply to the urbanised region in the southern part of the country. The population explosion is putting increasing pressure on quantitative and qualitative aspects of the groundwater resources. Preventing groundwater contamination caused by surface waters requires a thorough understanding of surface-water/groundwater interactions, especially the interactions between the Mio-Pliocene aquifer and surface waters. This study aimed to investigate the interactions between groundwater and surface waters along the major rivers (Sô River and Ouémé Stream) and brooks in the Ouémé Delta. Field campaigns identified 75 springs located in the valleys which feed the rivers, and thus maintain their base flow. The piezometric results indicated, through flow direction assessment, that the Mio-Pliocene aquifer feeds Ouémé Stream and Sô River. Chemical analyses of groundwater and surface waters show similar chemical facies, and changes in the chemical composition in groundwater are also observed in the surface waters. Moreover, the isotopic signatures of surface waters are similar to those of the groundwater and springs, which led to the identification of potential groundwater discharge areas. As a result of groundwater discharge into surface waters, the fraction of groundwater in the surface water is more than 66% in the brooks, regardless of the season. In the Ouémé Stream and Sô River, the fraction of groundwater is 0–21% between June and September, while from October to March it is 47–100%.