Recent evolution of Lake Arreo,northern Spain: influences of land use change and climate     

Juan Pablo Corella  Adel El Amrani  Javier Sigró  Mario Morellón  Eugenio Rico  Blas Lorenzo Valero-Garcés 《Journal of Paleolimnology》2011,46(3):469-485

We present a high-resolution, multiproxy reconstruction of the depositional history of Lake Arreo, northern Spain, for the last 60 years. We conducted sedimentological, geochemical and diatom analyses in short cores and made a detailed comparison with regional instrumental climate data (1952–2007), limnological monitoring of the lake (1992–2008) and recent land use changes that affect the lake catchment. Chronology is based on “floating” discontinuous varve counts and ¹³⁷Cs and ¹⁴C dates. Four periods were identified in the Lake Arreo recent history: (1) prior to 1963, varved facies intercalated with fine turbidite deposits, and diatom assemblages dominated by Cyclotella taxa indicate predominantly meromictic conditions, (2) from 1964 to 1978, permanent anoxia persisted in bottom waters, as shown by similar facies and diatom assemblages as before, though detrital layers were coarser, (3) from 1979 to 1994, sediment delivery to the lake increased and laminated, clastic facies were deposited, and (4) from 1995 to 2008, dominance of massive facies and an increase in Fragilaria tenera and Achnanthes minutissima reflect relatively lower lake levels, less frequent bottom anoxia with more frequent water column mixing, similar to modern conditions. The period 1952–1979 was a time of meromixis and varved facies deposition, and was characterized by higher rainfall and less intense agricultural pressure in the watershed. There were two short humid periods (1992–1993 and 1996–1998) when monitoring data show more anoxic weeks per year and relatively higher lake levels. Increased cultivation of small landholdings in 1963, and particularly after 1979, caused a large increase in sediment delivery to the lake. The inferred lake evolution is in agreement with monitoring data that suggest a transition from dominantly meromictic conditions prior to 1993–1994 to a predominantly monomictic pattern of circulation since then, particularly after 2000. The synergistic effects of intensive water extraction for irrigation and lower rainfall since 1979, and particularly since 1994, brought the long period of meromictic conditions in Lake Arreo to an end. Water balance and sediment delivery to the lake are dominant factors that control the limnological and mixing conditions in Lake Arreo and they must be considered in management and restoration plans.  相似文献   

Provenance analysis of the Paleozoic sequences of the northern Gondwana margin in NW Iberia: Passive margin to Variscan collision and orocline development     

Daniel Pastor-Galán  Gabriel Gutiérrez-Alonso  J. Brendan Murphy  Javier Fernández-Suárez  Mandy Hofmann  Ulf Linnemann 《Gondwana Research》2013,23(3):1089-1103

The Cantabrian Zone of NW Iberia preserves a voluminous, almost continuous, sedimentary sequence that ranges from Neoproterozoic to Early Permian in age. Its tectonic setting is controversial and recent hypotheses include (i) passive margin deposition along the northern margin of Gondwana or (ii) an active continental margin or (iii) a drifting ribbon continent. In this paper we present detrital zircon U–Pb laser ablation age data from 13 samples taken in detrital rocks from the Cantabrian Zone sequence ranging from Early Silurian to Early Permian in depositional age. The obtained results, together with previously published detrital zircon ages from Ediacaran–Ordovician strata, allow a comprehensive analysis of changing provenance through time. Collectively, these data indicate that this portion of Iberia was part of the passive margin of Gondwana at least from Ordovician to Late Devonian times. Zircon populations in all samples show strong similarities with the Sahara Craton and with zircons found in Libya, suggesting that NW Iberia occupied a paleoposition close to those regions of present-day northern Africa during this time interval. Changes in provenance in the Late Devonian are attributed to the onset of the collision between Gondwana and Laurussia.Additionally, the Middle Carboniferous to Permian samples record populations consistent with the recycling of older sedimentary sequences and exhumation of the igneous rocks formed before and during the Variscan orogeny. Late-Devonian to Permian samples yield zircon populations that reflect topographic changes produced during the Variscan orogeny and development of the lithospheric scale oroclinal buckling.  相似文献   

Hydrogeological research on intensively exploited deep aquifers in the ‘Loma de Úbeda’ area (Jaén, southern Spain)     

Antonio González-Ramón  Javier Rodríguez-Arévalo  Sergio Martos-Rosillo  Javier Gollonet 《Hydrogeology Journal》2013,21(4):887-903

The intensive use of groundwater for irrigation in the area of Úbeda (‘Loma de Úbeda’, Jaén, southern Spain) has transformed an area of traditionally rain-fed dry farmland into fields with some of the highest olive oil productivity in the world. Early hydrogeological research studies, initiated just after the beginning of the groundwater exploitation, revealed that the water was collected from three different overlapping aquifers occupying an area of over 1,100 km², with the lower aquifers located at depths from 300 to over 700 m in an area of 440 km². Multidisciplinary research, based on geological characterization, and piezometric, hydrochemical and isotopic data, has led to a conceptual model of functioning in this complex hydrogeological system. The proposed model allows for the identification of the recharge areas, and the discharge, which is at present mainly associated with the groundwater pumping. Areas of mixing of waters from the different aquifers and the main hydrogeochemical processes affecting groundwater quality are described.  相似文献   

Analysis of anisotropy of magnetic susceptibility in iron-oolitic beds: a potential tool for paleocurrent identification     

Óscar Pueyo Anchuela  Javier Ramajo Cordero  Andrés Gil Imaz  Guillermo Meléndez Hevia 《International Journal of Earth Sciences》2013,102(4):1131-1149

A combined sedimentological, shape-preferred orientation and anisotropy of magnetic susceptibility (AMS) analysis has been performed at the Arroyofrío Bed (Callovian–Oxfordian boundary level) in the locality of Moneva (Iberian Range, NE Spain). The Arroyofrío bed is a widespread iron-ooid limestone interval forming a condensed sequence. The present study has focused on the analysis of the potential presence of a preferred ooid orientation at the Arroyofrío bed. The obtained data show that ooids were originally ellipsoidal and had an imbricate disposition with respect to the bedding/lamination surface. The main ooid orientation within the bedding plane shows a NNE–SSW trend. Results of AMS analyses show a magnetic foliation parallel or slightly imbricated with respect to bedding and magnetic lineation parallel to the main ooid orientation. Magnetic mineralogy of studied samples shows that AMS is mainly controlled by magnetite with minor contributions of hematite and paramagnetic minerals (that can reach contributions of 35 %). The analyzed ooids show axial ratios between 1.4 and 2.8 (intrinsic anisotropy), while the anisotropy of their distribution shows lower anisotropies (e.g., Rs = 1.15) or very low values of the anisotropic magnetic parameters (e.g., P′ < 1.01). Sedimentary texture, matrix features, bioturbation and fossil content influenced both ooid main orientation and the magnetic fabric. Magnetic lineation and main orientation of long ooid axes are transverse to the inferred coastline in the studied area and parallel to the expected paleocurrent direction with respect to the Ejulve-Maestrazgo paleogeographic high. The direct correlation between AMS magnetic lineation and the ooid analysis permits to demonstrate that the paleocurrent imprint can be recorded by means of AMS despite the highly ferromagnetic context fabric and at coarse deposits. Obtained results support the interest and reliability of AMS to unravel paleocurrent imprints for paleogeographic reconstructions.  相似文献   

Tier-based approaches for landslide susceptibility assessment in Europe   总被引：3，自引：2，他引：1  

Andreas Günther  Paola Reichenbach  Jean-Philippe Malet  Miet Van Den Eeckhaut  Javier Hervás  Claire Dashwood  Fausto Guzzetti 《Landslides》2013,10(5):529-546

In the framework of the European Soil Thematic Strategy and the associated proposal of a Framework Directive on the protection and sustainable use of soil, landslides were recognised as a soil threat requiring specific strategies for priority area identification, spatial hazard assessment and management. This contribution outlines the general specifications for nested, Tier-based geographical landslide zonings at small spatial scales to identify priority areas susceptible to landslides (Tier 1) and to perform quantitative susceptibility evaluations within these (Tier 2). A heuristic, synoptic-scale Tier 1 assessment exploiting a reduced set of geoenvironmental factors derived from common pan-European data sources is proposed for the European Union and adjacent countries. Evaluation of the susceptibility estimate with national-level landslide inventory data suggests that a zonation of Europe according to, e.g. morphology and climate, and performing separate susceptibility assessments per zone could give more reliable results. To improve the Tier 1 assessment, a geomorphological terrain zoning and landslide typology differentiation are then applied for France. A multivariate landslide susceptibility assessment using additional information on landslide conditioning and triggering factors, together with a historical catalogue of landslides, is proposed for Tier 2 analysis. An approach is tested for priority areas in Italy using small administrative mapping units, allowing for relating socioeconomic census data with landslide susceptibility, which is mandatory for decision making regarding the adoption of landslide prevention and mitigation measures. The paper concludes with recommendations on further work to harmonise European landslide susceptibility assessments in the context of the European Soil Thematic Strategy.  相似文献   

Improvements to Remote Sensing Using Fuzzy Classification, Graphs and Accuracy Statistics     

Daniel Gómez  Javier Montero  Gregory Biging 《Pure and Applied Geophysics》2008,165(8):1555-1575

This paper puts together some techniques that have been previously developed by the authors, but separately, relative to fuzzy classification within a remote sensing setting. Considering that each image can be represented as a graph that defines proximity between pixels, certain distances between the characteristic of contiguous pixels are defined on such a graph, so a segmentation of the image into homogeneous regions can be produced by means of a particular algorithm. Such a segmentation can be then introduced as information, previously to any classification procedure, with an expected significative improvement. In particular, we consider specific measures in order to quantify such an improvement. This approach is being illustrated with its application into a particular land surface problem.  相似文献   

The life history of Serratella ignita (Poda, 1761) (Insecta: Ephemeroptera) in a temporary and permanent Mediterranean stream     

Manuel J. López-Rodríguez  J. Manuel Tierno de Figueroa  Javier Alba-Tercedor 《Aquatic Sciences - Research Across Boundaries》2009,71(2):179-188

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Tectonics of an extinct ridge-transform intersection,Drake Passage (Antarctica)     

Maldonado  Andrés  Carlos Balanyá  Juan  Barnolas  Antonio  Galindo-Zaldívar  Jesús  Hernández  Javier  Jabaloy  Antonio  Livermore  Roy  Miguel Martínez-Martínez  José  Rodríguez-Fernández  José  Sanz de Galdeano  Carlos  Somoza  Luis  Suriñach  Emma  Viseras  César 《Marine Geophysical Researches》2000,21(1-2):43-68

New swath bathymetric, multichannel seismic and magnetic data reveal the complexity of the intersection between the extinct West Scotia Ridge (WSR) and the Shackleton Fracture Zone (SFZ), a first-order NW-SE trending high-relief ridge cutting across the Drake Passage. The SFZ is composed of shallow, ridge segments and depressions, largely parallel to the fracture zone with an `en echelon' pattern in plan view. These features are bounded by tectonic lineaments, interpreted as faults. The axial valley of the spreading center intersects the fracture zone in a complex area of deformation, where N120° E lineaments and E–W faults anastomose on both sides of the intersection. The fracture zone developed within an extensional regime, which facilitated the formation of oceanic transverse ridges parallel to the fracture zone and depressions attributed to pull-apart basins, bounded by normal and strike-slip faults.On the multichannel seismic (MCS) profiles, the igneous crust is well stratified, with numerous discontinuous high-amplitude reflectors and many irregular diffractions at the top, and a thicker layer below. The latter has sparse and weak reflectors, although it locally contains strong, dipping reflections. A bright, slightly undulating reflector observed below the spreading center axial valley at about 0.75 s (twt) depth in the igneous crust is interpreted as an indication of the relict axial magma chamber. Deep, high-amplitude subhorizontal and slightly dipping reflections are observed between 1.8 and 3.2 s (twt) below sea floor, but are preferentially located at about 2.8–3.0 s (twt) depth. Where these reflections are more continuous they may represent the Mohorovicic seismic discontinuity. More locally, short (2–3 km long), very high-amplitude reflections observed at 3.6 and 4.3 s (twt) depth below sea floor are attributed to an interlayered upper mantle transition zone. The MCS profiles also show a pattern of regularly spaced, steep-inclined reflectors, which cut across layers 2 and 3 of the oceanic crust. These reflectors are attributed to deformation under a transpressional regime that developed along the SFZ, shortly after spreading ceased at the WSR. Magnetic anomalies 5 to 5 E may be confidently identified on the flanks of the WSR. Our spreading model assumes slow rates (ca. 10–20 mm/yr), with slight asymmetries favoring the southeastern flank between 5C and 5, and the northwestern flank between 5 and extinction. The spreading rate asymmetry means that accretion was slower during formation of the steeper, shallower, southeastern flank than of the northwestern flank.  相似文献   

Long-lasting floods buffer the thermal regime of the Pampas   总被引：1，自引：0，他引：1  

Javier?HouspanossianEmail author  Sylvain?Kuppel  Marcelo?Nosetto  Carlos?Di Bella  Patricio?Oricchio  Mariana?Barrucand  Matilde?Rusticucci  Esteban?Jobbágy 《Theoretical and Applied Climatology》2018,131(1-2):111-120

The presence of large water masses influences the thermal regime of nearby land shaping the local climate of coastal areas by the ocean or large continental lakes. Large surface water bodies have an ephemeral nature in the vast sedimentary plains of the Pampas (Argentina) where non-flooded periods alternate with flooding cycles covering up to one third of the landscape for several months. Based on temperature records from 17 sites located 1 to 700 km away from the Atlantic coast and MODIS land surface temperature data, we explore the effects of floods on diurnal and seasonal thermal ranges as well as temperature extremes. In non-flooded periods, there is a linear increase of mean diurnal thermal range (DTR) from the coast towards the interior of the region (DTR increasing from 10 to 16 K, 0.79 K/100 km, r ² = 0.81). This relationship weakens during flood episodes when the DTR of flood-prone inland locations shows a decline of 2 to 4 K, depending on surface water coverage in the surrounding area. DTR even approaches typical coastal values 500 km away from the ocean in the most flooded location that we studied during the three flooding cycles recorded in the study period. Frosts-free periods, a key driver of the phenology of both natural and cultivated ecosystems, are extended by up to 55 days during floods, most likely as a result of enhanced ground heat storage across the landscape (~2.7 fold change in day-night heat transfer) combined with other effects on the surface energy balance such as greater night evaporation rates. The reduced thermal range and longer frost-free periods affect plant growth development and may offer an opportunity for longer crop growing periods, which may not only contribute to partially compensating for regional production losses caused by floods, but also open avenues for flood mitigation through higher plant evapotranspirative water losses.  相似文献   

Coupled thermo-hydro-bio-geochemical reactive transport model of CERBERUS heating and radiation experiment in Boom clay     

Guoxiang Zhang  Javier Samper  Luis Montenegro 《Applied Geochemistry》2008

Final disposal of high-level radioactive waste in deep repositories in clay formations is being considered by several countries. Repository safety assessment requires the use of numerical models of groundwater flow, solute transport and chemical processes. These models are being developed from data and knowledge gained from in situ experiments such as the CERBERUS experiment carried out at the HADES facility excavated in the Boom clay formation at Mol (Belgium). This long-term experiment is aimed at evaluating the effect of heating and radiation in Boom clay. The test was performed in a cased well drilled at 223 m depth and lasted from 1989 to 1994. A ⁶⁰Co source of 400 TBq and two heaters were emplaced inside the well. Dose rate, temperature, porewater pressure and pH/Eh were measured in situ during the experiment and gas and porewater samples were taken for chemical analyses. Here a coupled thermo-hydro-geochemical (THC) model of the CERBERUS experiment is presented which accounts simultaneously for heating, radiation, solute diffusion and a suite of geochemical reactions including: aqueous complexation, acid–base, redox, mineral dissolution/precipitation, cation exchange and gas dissolution/ex-solution. Computed results indicate that heating and radiation causes a slight oxidation, a decrease in pH, slight changes in porewater chemistry and pyrite dissolution near the well. THC model results follow the general evolution of chemical data, but cannot fit SO₄ data. Model discrepancies are partly overcome when microbially-mediated Fe and SO₄ reduction are taken into account in a coupled thermo-hydro-bio-geochemical (THBC) model. This THBC model captures the trends of geochemical data, improves the fit to dissolved SO₄ and predicts pyrite precipitation, a process observed near the CERBERUS well. The ability of the THBC numerical model to reproduce the overall trends of geochemical data of the CERBERUS experiment provides confidence in such a model as a suitable tool for the long-term prediction of geochemistry in the near field of a HLW repository in clay. However, the small number of available chemical data throughout the experiment and the lack of DOC and microbial data allow only a partial validation of the THBC model.  相似文献