Runoff generation and routing on artificial slopes in a Mediterranean–continental environment: the Teruel coalfield,Spain     

Jos‐Manuel Nicolau 《水文研究》2002,16(3):631-647

The aim of this study was to identify the mechanisms of runoff generation and routing and their controlling factors at the hillslope scale, on artificial slopes derived from surface coal mining reclamation in a Mediterranean–continental area. Rainfall and runoff at interrill and microcatchment scales were recorded for a year on two slopes with different substrata: topsoil cover and overburden cover. Runoff coefficient and runoff routing from interrill areas to microcatchment outlets were higher in the overburden substratum than in topsoil, and greater in the most developed rill network. Rainfall volume is the major parameter responsible for runoff response on overburden, suggesting that this substratum is very impermeable—at least during the main rainfall periods of the year (late spring and autumn) when the soil surface is sealed. In such conditions, most rainfall input is converted into runoff, regardless of its intensity. Results from artificial rainfall experiments, conducted 3 and 7 years after seeding, confirm the low infiltration capacity of overburden when sealed. The hydrological response shows great seasonal variability on the overburden slope in accordance with soil surface changes over the year. Rainfall volume and intensities (I₃₀, I₆₀) explain runoff at the interrill scale on the topsoil slope, where rainfall experiments demonstrated a typical Hortonian infiltration curve. However, no correlation was found at the microcatchment level, probably because of the loss of functionality of the only rill as ecological succession proceeded. The runoff generation mechanism on the topsoil slope is more homogeneous throughout the year. Runoff connectivity, defined as the ratio between runoff rates recorded at the rill network scale and those recorded at the interrill area scale in every rainfall event, was also greater on the rilled overburden slope, and in the most developed rill network. The dense rill networks of the overburden slope guarantee very effective runoff drainage, regardless of rainfall magnitude. Rills drain overland flow from interrill‐sealed areas, reducing the opportunity of reinfiltration in areas not affected by siltation. Runoff generation and routing on topsoil slopes are controlled by grass cover and soil moisture content, whereas on overburden slopes rill network density and soil moisture content are the main controlling factors. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Groundwater behaviour in Madeira, volcanic island (Portugal)     

Susana Nascimento Prada  Manuel Oliveira da Silva  José Virgílio Cruz 《Hydrogeology Journal》2005,13(5-6):800-812

Madeira Island is a hot-spot originating from a mantle plume. K-Ar age determinations indicate that the emerged part of the island was generated during Post-Miocene times 6000–7000 years B.P. Groundwater occurs in perched-water bodies, spring discharge from them is high, about 3,650 l/s; in dike-impounded water and basal groundwater. Basal groundwater is exploited by tunnels (1,100 l/s) and wells (1,100 l/s). Hydraulic gradients range from 10^–4 to 10^–2 and transmissivity ranges from 1.16×10^–2 to 2.89×10^–1 m²/s, indicating the heterogeneity of the volcanic aquifers. Water mineralisation is variable, and electrical conductivity ranges from 50 to 3,300 S/cm. There is a difference between groundwater discharging from perched-water bodies (43–201 S/cm) and from basal groundwater (109–3,300 S/cm). Groundwater average pH is 7.37, with waters acid to slightly alkaline (6.13–8.4), and generally cold. Nevertheless, a few samples associated with fault zones can be classified as thermal waters.

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Resumen La Isla de Madeira tuvo origen en un punto caliente proveniente de una pluma del manto. Las dataciones K – Ar, indican que la parte emergida de la isla se formó durante en Post—Mioceno, hace unos 6000–7000 años. El agua subterránea se encuentra en acuíferos colgados, cuya descarga a través de manantiales es alta, alrededor de 3650 l/s; también como agua retenida en diques o bien como agua subterránea propiamente dicha. Esta última es explotada por túneles (1100 l/s) y pozos (1100 l/s). Los gradientes hidráulicos varían desde 10–4 hasta 10–2 y la transmisividad varía desde 1.16×10^–2 hasta 2.89×10^–1 m²/s, indicando la heterogeneidad de los acuíferos volcánicos. La mineralización de agua es variable y la conductividad eléctrica varía desde 50 mS/cm hasta 3300 mS/cm. Hay una diferencia entre el agua subterránea proveniente de acuíferos colgados (43–201 mS/cm) y aquella del acuífero principal (109–3300 mS/cm). El pH promedio para el agua subterránea es 7.37; con variación desde ácida hasta ligeramente alcalina (6.13–8.4), y es generalmente fría. Sin embargo unos pocos ejemplos asociados con zonas de falla, pueden ser clasificados como agua termal.

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Résumé Lîle de Madeira est un point chaud, provenant dun panache mantélique. Les datations par la méthode de K-Ar indiquent que la part émergée de lîle a été générée pendant le Post Miocène, il y a 6000–7000 ans. Les eaux souterraines sont cantonnées dans des aquifères perchées qui se déchargent par des sources à grands débits, avec des valeurs dapproximativement de 3500 l/s, ainsi que dans les dikes. Une importante quantité des eaux souterraine se trouve sur la forme deau de fonds, formant une nappe basale, qui est exploitée par des tunnels (1100 l/s) et par des puits (1100 l/s). Les gradients hydrauliques ont des valeurs dans lintervalle de 10^–2 à 10^–4, tandis que les transmissivités se rangent entre 1.16×10^–2 m²/s et 2.81×10^–1 m²/s, ce quindique la hétérogénéité de laquifère volcanique. La minéralisation des eaux est aussi variable avec des conductivités électriques qui se rangent ente 50 mS/cm et 3300 mS/cm. Il y a une différence entre la conductivité des eaux provenant des aquifères perchées (30–201 mS/cm) par rapport à la conductivité les eaux de la nappe basale (109–3300 mS/cm). Le pH moyen est de 7.37 avec des valeurs de 6.13 pour les eaux acides et de 8.4 pour les eaux à faible alcalinité. En général il sagit des eaux froides, mais quelques échantillons provenant des zones faillées peuvent être classifiés comme des eaux thermales.

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Surface area, porosity and water adsorption properties of fine volcanic ash particles   总被引：1，自引：1，他引：0  

Pierre Delmelle  Frédéric Villiéras  Manuel Pelletier 《Bulletin of Volcanology》2005,67(2):160-169

Our understanding on how ash particles in volcanic plumes react with coexisting gases and aerosols is still rudimentary, despite the importance of these reactions in influencing the chemistry and dynamics of a plume. In this study, six samples of fine ash (<100 m) from different volcanoes were measured for their specific surface area, a_s, porosity and water adsorption properties with the aim to provide insights into the capacity of silicate ash particles to react with gases, including water vapour. To do so, we performed high-resolution nitrogen and water vapour adsorption/desorption experiments at 77 K and 303 K, respectively. The nitrogen data indicated a_s values in the range 1.1–2.1 m²/g, except in one case where a a_s of 10 m²/g was measured. This high value is attributed to incorporation of hydrothermal phases, such as clay minerals, in the ash surface composition. The data also revealed that the ash samples are essentially non-porous, or have a porosity dominated by macropores with widths >500 Å. All the specimens had similar pore size distributions, with a small peak centered around 50 Å. These findings suggest that fine ash particles have relatively undifferentiated surface textures, irrespective of the chemical composition and eruption type. Adsorption isotherms for water vapour revealed that the capacity of the ash samples for water adsorption is systematically larger than predicted from the nitrogen adsorption a_s values. Enhanced reactivity of the ash surface towards water may result from (i) hydration of bulk ash constituents; (ii) hydration of surface compounds; and/or (iii) hydroxylation of the surface of the ash. The later mechanism may lead to irreversible retention of water. Based on these experiments, we predict that volcanic ash is covered by a complete monolayer of water under ambient atmospheric conditions. In addition, capillary condensation within ash pores should allow for deposition of condensed water on to ash particles before water reaches saturation in the plume. The total mass of water vapour retained by 1 g of fine ash at 0.95 relative water vapour pressure is calculated to be ~10^–2 g. Some volcanic implications of this study are discussed.Editorial responsibility: J. Gilbert  相似文献   

Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: VII. Carbonate isotope geochemistry as a record of riverine runoff     

David?L.?DettmanEmail author  Manuel?R.?Palacios-Fest  Hudson?H.?Nkotagu  Andrew?S.?Cohen 《Journal of Paleolimnology》2005,34(1):93-105

Evaporation dominates the removal of water from Lake Tanganyika, and therefore the oxygen isotope composition of lake water has become very positive in comparison to the waters entering the lake. The surface water in Lake Tanganyika has remained relatively unchanged over the last 30 years with a seasonal range of +3.2 to +3.5 VSMOW. Water from small rivers entering the lake seems to have a ¹⁸O value between –3.5 and –4.0, based on scattered measurements. The two largest catchments emptying into the lake deliver water that has a ¹⁸O value between these two extremes. This large contrast is the basis of a model presented here that attempts to reconstruct the history of runoff intensity based on the ¹⁸O of carbonate shells from Lake Tanganyika cores. In order to use biogenic carbonates to monitor changes in the ¹⁸O of mixing-zone water, however, the oxygen isotope fractionation between water and shell carbonate must be well understood. The relatively invariant environmental conditions of the lake allow us to constrain the fractionation of both oxygen and carbon isotope ratios. Although molluskan aragonitic shell ¹⁸O values are in agreement with published mineral-water fractionations, ostracode calcite is 1.2 more positive than that of inorganic calcite precipitated under similar conditions. Ostracode shell ¹⁸O data from two cores from central Lake Tanganyika suggest that runoff decreased in the first half of this millennium and has increased in the last century. This conclusion is poorly constrained, however, and much more work needs to be done on stable isotope variation in both the waters and carbonates of Lake Tanganyika. We also compared the ¹³C of shells against predicted values based solely on the ¹³C of lake water dissolved inorganic carbon (DIC). The ostracode Mecynocypria opaca is the only ostracode or mollusk that falls within the predicted range. This suggests that M. opaca has potential for reconstructing the carbon isotope ratio of DIC in Lake Tanganyika, and may be a useful tool in the study of the history of the lakes productivity and carbon cycle.  相似文献   

Preliminary Report On Distribution of Karst Landscapes In Cuba and Their Relation To Geology *     

Manuel A. Iturralde-Vinent 《The Professional geographer》1967,19(4):208-209

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Future regional projections of extreme temperatures in Europe: a nonstationary seasonal approach     

Maria Dolores Frías  Roberto Mínguez  Jose Manuel Gutiérrez  Fernando J. Méndez 《Climatic change》2012,113(2):371-392

This paper analyzes changes of maximum temperatures in Europe, which are evaluated using two state-of-the-art regional climate models from the EU ENSEMBLES project. Extremes are expressed in terms of return values using a time-dependent generalized extreme value (GEV) model fitted to monthly maxima. Unlike the standard GEV method, this approach allows analyzing return periods at different time scales (monthly, seasonal, annual, etc). The study focuses on the end of the 20th century (1961?C2000), used as a calibration/validation period, and assesses the changes projected for the period 2061?C2100 considering the A1B emission scenario. The performance of the regional models is evaluated for each season of the calibration period against the high-resolution gridded E-OBS dataset, showing a similar South-North gradient with larger values over the Mediterranean basin. The inter-RCM changes in the bias pattern with respect to the E-OBS are larger than the bias resulting from a change in the boundary conditions from ERA-40 to ECHAM5 20c3m. The maximum temperature response to increased green house gases, as projected by the A1B scenario, is consistent for both RCMs. Under that scenario, results indicate that the increments for extremes (e.g. 40-year return values) will be two or three times higher than those for the mean seasonal temperatures, particularly during Spring and Summer in Southern Europe.  相似文献   

Reducing greenhouse gas emissions from deforestation and forest degradation in developing countries: revisiting the assumptions     

Esteve Corbera  Manuel Estrada  Katrina Brown 《Climatic change》2010,100(3-4):355-388

The United Nations Framework on Climate Change (UNFCCC), at its thirteenth meeting in 2005 (COP-11), agreed to start a work program to explore a range of policy approaches and positive incentives for Reducing Emissions from Deforestation and Degradation (REDD). This process was further encouraged in the 2007 COP-13 with the explicit consideration of REDD activities as a means to enhance mitigation action by developing countries in the future. This paper outlines the context of this ongoing political process by reviewing the science indicating that land-use change is a key contributor of greenhouse emissions globally and the assumptions that REDD activities may be competitive—in terms of cost effectiveness—in comparison to other mitigation options. The paper then examines REDD proposals submitted by Parties before COP-13 and identifies key economic, technological, methodological and institutional challenges associated with their implementation. These proposals are discussed in the light of major drivers of deforestation and ongoing efforts to address deforestation. This reveals another set of challenges which, if not taken into account, may undermine REDD effectiveness. The paper aims to aid the policy process and contribute to the best possible design of a REDD framework under the future climate regime.  相似文献   

Simulated decadal oscillations of the Atlantic meridional overturning circulation in a cold climate state     

Masakazu Yoshimori  Christoph C. Raible  Thomas F. Stocker  Manuel Renold 《Climate Dynamics》2010,34(1):101-121

The significance of the Atlantic meridional overturning circulation (MOC) for regional and hemispheric climate change requires a complete understanding using fully coupled climate models. Here we present a persistent, decadal oscillation in a coupled atmosphere–ocean general circulation model. While the present study is limited by the lack of comparisons with paleo-proxy records, the purpose is to reveal a new theoretically interesting solution found in the fully-coupled climate model. The model exhibits two multi-century-long stable states with one dominated by decadal MOC oscillations. The oscillations involve an interaction between anomalous advective transport of salt and surface density in the North Atlantic subpolar gyre. Their time scale is fundamentally determined by the advection. In addition, there is a link between the MOC oscillations and North Atlantic Oscillation (NAO)-like sea level pressure anomalies. The analysis suggests an interaction between the NAO and an anomalous subpolar gyre circulation in which sea ice near and south of the Labrador Sea plays an important role in generating a large local thermal anomaly and a meridional temperature gradient. The latter induces a positive feedback via synoptic eddy activity in the atmosphere. In addition, the oscillation only appears when the Nordic Sea is completely covered by sea ice in winter, and deep convection is active only near the Irminger Sea. Such conditions are provided by a substantially colder North Atlantic climate than today.  相似文献   

Impacts of global environmental change and aquaculture expansion on marine ecosystems     

Gorka Merino  Manuel Barange  Christian Mullon  Lynda Rodwell 《Global Environmental Change》2010,20(4):586-596

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The Jiddat al Harasis 073 strewn field,Sultanate of Oman     

Edwin GNOS  Silvio LORENZETTI  Otto EUGSTER  A. J. Timothy JULL  Beda A. HOFMANN  Ali Al‐KATHIRI  Manuel EGGIMANN 《Meteoritics & planetary science》2009,44(3):375-387

Abstract— The recently discovered Jiddat al Harasis (JaH) 073 strewn field is the largest found so far in the Sultanate of Oman, covering an area of 19 × 6 km. The 3463 single stones collected range in weight from 52.2 kg down to <1 g (total weight 600.8 kg) and show a pronounced mass sorting. The strewn field shape can be approximated by a NW‐SE‐oriented ellipsoid, indicating an atmospheric entry from SE at a low angle relative to the surface. The meteorite belongs to the L6 ordinary chondrite group and shows S4 average shock grade. Smaller stones generally show a higher weathering grade resulting in a spread from W2 and W4. Enhanced weathering of the stones causing fragmentation after the fall is observed in sandy depressions. Five ¹⁴C measurements on stones of variable size and weathering grade yielded ¹⁴C from 3.8 to 49.9 dpm/kg. Three samples give a ¹⁴C/ ¹⁰Be age consistent with about 14.4 ka. For two samples the cosmogenic, trapped, and radiogenic noble gases were measured. The ratio of the ⁴He and ⁴⁰Ar gas retention ages of 0.29 ± 0.10 and that of the ³He and ²¹Ne cosmic ray exposure ages of 0.36 ± 0.08 Ma indicate that JaH 073 experienced a complex exposure history and lost ⁴He and ⁴⁰Ar due to a major collision. Fragmentation statistics indicate a single major atmospheric disruption and an originally relatively spherical shape of the object. Assuming the material collected represents the majority of fallen mass, and 90–99% of the original weight was lost by ablation, the pre‐atmospheric minimum radius of the meteoroid with density 3.4 g cm^?3would have been at least 75 cm.  相似文献