Estimating the role of a ditch network in groundwater recharge in a Mediterranean catchment using a water balance approach

Water balance variables were monitored in a farmed Mediterranean catchment characterized by a dense ditch network to allow for the separate estimation of the diffuse and concentrated recharge terms during flood events. The 27 ha central part of the catchment was equipped with (i) rain gauges, (ii) ditch gauge stations, (iii) piezometers, (iv) neutron probes, and (v) an eddy covariance mast including a 3D sonic anemometer and a fast hygrometer. The water balance was calculated for two autumnal rain and flood events. We also estimated the uncertainty of this approach with Monte Carlo simulations. Results show, that although ditch area represents only 6% of the total study area, concentrated recharge appeared to be the main source of groundwater recharge. Indeed, it was 40–50% of the total groundwater recharge for autumnal events, which are the major annual recharge events. This indicate that both, concentrated and diffuse recharge should be taken into account in any hydrological modeling approach for Mediterranean catchments. This also means that, since they collect overland flow that is often largely contaminated by chemicals, ditches may be a place where groundwater contamination is likely to occur. The uncertainty analysis indicates that recharge estimates based on water balance exhibit large uncertainty ranges. Nevertheless, Monte Carlo simulations showed that concentrated recharge was higher than expected based on their area.     

Numerical modeling of centrifuge cyclic lateral pile load experiments

To gain insight into the inelastic behavior of piles, the response of a vertical pile embedded in dry sand and subjected to cyclic lateral loading was studied experimentally in centrifuge tests conducted in Laboratoire Central des Ponts et Chaussées. Three types of cyclic loading were applied, two asymmetric and one symmetric with respect to the unloaded pile. An approximately square-root variation of soil stiffness with depth was obtained from indirect in-flight density measurements, laboratory tests on re...     

In situ Measurement of H2O and CH4 with Telecommunication Laser Diodes in the Lower Stratosphere: Dehydration and Indication of a Tropical Air Intrusion at Mid-Latitudes

Telecommunication laser diodes emitting near 1.39 m and 1.65 m in combination with direct-differential absorption spectroscopy are efficient tools to monitor in situ stratospheric H₂O andCH₄ with a good precision error (a few percents), a high temporal resolution (ranging from 10 ms to 1 s), a large dynamic range in the concentration measurements (four orders of magnitude) and a high selectivity in the analyte species. To illustrate the capability of laser probing technique, we report balloonborne H₂Oand CH₄ simultaneous measurements obtained on October 2001 atmidlatitudes (43° N). The H₂O vertical profile achieved with the lasersensor in the lower stratosphere is compared with the H₂O data yielded by a balloonborne frost-point hygrometer. The total hydrogen mixing ratio in the lower stratosphere, 2[CH₄] + [H₂O], appears to beconstant at 7.5 ± 0.1 ppmv. Nevertheless, an unexpected largedehydration of 0.5 ppmv was detected by both the laser sensor and thehygrometer between 16 km and 23 km. We suspect the occurrence of a tropicalair intrusion into mid-latitudes. We support this interpretation using a high-resolution advection model for potential vorticity.     

The fate of nitrogen and sulfur in hard-rock aquifers as shown by sulfate-isotope tracing

Stable SO₄ isotopes (δ³⁴S_-SO4 and δ¹⁸O_-SO4), and more occasionally δ¹⁵N_-NO3 were studied in groundwater from seven hard-rock aquifer catchments. The sites are located in Brittany (France) and all are characterized by intensive agricultural activity. The purpose of the study was to investigate the potential use of these isotopes for highlighting the fate of both SO₄ and NO₃ in the different aquifer compartments. Nitrate-contaminated groundwater occurs in the regolith; δ³⁴S fingerprints the origin of SO₄, such as atmospheric deposition and fertilizers, and δ¹⁸O_-SO4 provides evidence of the cycling of S within soil. The correlation between the δ¹⁸O_-SO4 of sulfates and the δ¹⁵N_-NO3 of nitrates suggests that S and N were both cycled in soil before being leached to groundwater. Autotrophic and heterotrophic denitrification was noted in fissured aquifers and in wetlands, respectively, the two processes being distinguished on the basis of stable SO₄ isotopes. During autotrophic denitrification, both δ³⁴S_-SO4 and δ¹⁸O_-SO4 decrease due to the oxidation of pyrite and the incorporation of O from the NO₃ molecule in the newly formed SO₄. Within wetlands, fractionation occurs of O isotopes on SO₄ in favour of lighter isotopes, probably through reductive assimilation processes. Fractionation of S isotopes is negligible as the redox conditions are not sufficiently reductive for dissimilatory reduction. δ³⁴S_-SO4 and δ¹⁸O_-SO4 data fingerprint the presence of a NO₃-free brackish groundwater in the deepest parts of the aquifer. Through mixing with present-day denitrified groundwater, this brackish groundwater can contribute to significantly increase the salinity of pumped water from the fissured aquifer.     

Beyond nationalism: Three visions of the European Union and their implications for the linguistic regime of its institutions

The linguistic diversity in the European Union is generally viewed as an essential component of the European identity, but the linguistic regime of the EU institutions (with eleven official and working languages) is not undisputed. In addition, the upcoming enlargements will complicate greatly the continuation of the present practices as new Member States bring new official languages. As a result, the debate about possible reforms is likely to be boosted by the necessity to prepare EU institutions for further enlargment. The present regime of institutional multilingualism is criticised from different angles, resulting in three options for the future. In this paper the linguistic regime of EU institutions is discussed in relation to general ideas about the nature of this supranational political system. Supranationalism is treated here as a program to supersede nationalism. Three variants are distinguished: pacified nationalism, neo-nationalism and post-nationalism. The paper examines how these different visions of Europe shed different lights on the issue of multilingualism (in terms of communication, identity and power) and its institutionalisation in the linguistic regime of the core instituions of the European Union. Although the three models are compatible with several arrangements, they support or oppose them for different reasons. Besides, they differ regarding the significance of the linguistic regime of the EU institutions for the whole polity and their ability to steer linguistic practices.     

Grid-group cultural theory: an introduction

This article offers an introduction to grid-group cultural theory (also known as grid-group analysis, Cultural Theory or theory of socio-cultural viability), an approach that has been developed over the past thirty years in the work of the British anthropologists Mary Douglas and Michael Thompson, the American political scientist Aaron Wildavsky, and many others. This assessment begins with a presentation of the main claims of the theory, distinguishing two characteristic breads of grid-group cultural theory, in the one it is conceived as a heuristic device, in the other it is seen as a full explanatory theory. This brief is followed by a discussion of the typology generated by the theory. This includes a presentation of the two dimensions of sociality it posits, the cultural map they produce, as well as the four (or five) cultural types derived from them and their designations. The article proceeds with a discussion of key issues including the incorporation of other typologies (such as the one developed to analyse myths of nature), the relations between cultures or rationalities and several methodological issues. Finally the article introduces the contributions to this special issue of the GeoJournal. This revised version was published online in August 2006 with corrections to the Cover Date.     

Monitoring fluid substitution in rock samples from noise correlation

An alternative laboratory technique to measure the elastic constants of solid samples, based on the analysis of the cross‐correlation spectra of the vibratory response of randomly excited short solid cylinders, has been recently proposed. The aim of this paper is to check the ability of the technique called passive ultrasonic interferometry to monitor fluid substitution in different rock samples. Velocity variations due to fluid substitution are easily measured if the wave attenuation in the fluid‐saturated rock is not too large (typically in rocks with few cracks or microfractures). The experimental results are in agreement with the predictions of Biot–Gassmann poroelastic theory. The effect of substituting water with a stiffer saturating fluid, such as ethylene glycol, is to increase the overall bulk modulus of the rock, without any substantial effect on shear modulus. Furthermore, the experimental results compare well with those obtained independently with conventional pulse‐transmission technique using ultrasonic transducers. However, the measured pulse‐transmission bulk moduli are slightly larger than the corresponding measured ultrasonic interferometry moduli, with the deviation increasing with increasing fluid viscosity. This can be explained by dispersion due to wave‐induced flow of the viscous fluid since pulse‐transmission experiments involve higher frequencies than ultrasonic interferometry experiments.