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Assessment of two non-invasive techniques for measuring turbulent benthic fluxes in a shallow lake
No full textInternational audienceBenthic fluxes refer to the exchange rates of nutrients and other compounds between the water column and the sediment bed in aquatic ecosystems. Their quantification contributes to our understanding of aquatic ecosystem functioning. Near-bed hydrodynamics plays an important role at the sediment-water interface, especially in shallow lakes, but it is poorly considered by traditional measuring techniques of flux quantification, such as sediment incubations. Thus, alternative sampling techniques are needed to characterize key benthic fluxes under in-situ hydrodynamic conditions. This study aimed to evaluate the performance of two promising methods: relaxed eddy accumulation (REA) and mass transfer coefficient (MTC). We applied them in a hyper-eutrophic shallow lake to measure the fluxes of ammonium, phosphate, iron, and manganese ions. For the first time, REA revealed hourly nutrient flux variations, indicating a strong lake biogeochemical dynamics at short time-scales. Daily average fluxes are of similar orders of magnitude for REA and MTC for ammonium (24 and 42 mmol m2 d-1), manganese (1.0 and 0.8), and iron (0.8 and 0.7) ions. They are one order of magnitude higher than fluxes estimated from sediment incubations, due to the difficulty in reproducing in-situ oxygen and hydrodynamic conditions in the laboratory. Although the accuracy of both techniques needs to be improved, the results revealed their potential: REA follows the short-term biogeochemical dynamics of sediments, while MTC could be widely used for lake monitoring because of its simpler implementation
Inequality bands: Seventy-five years of measuring income inequality in latin america
No full textDrawing on a comprehensive compilation of quantile shares and inequality measures for 34 countries, including over 5,600 estimated Gini coefficients, we review the measurement of income inequality in Latin America and the Caribbean over the last seven decades. Although the evidence from the first quarter century – roughly until the 1970s – is too fragmentary and difficult to compare, clearer patterns emerge for the last fifty years. The central feature of these patterns is a broad inverted U curve, with inequality rising in most countries prior to the 1990s, and falling during the early 21st Century, at least until the mid-2010s, when trends appear to diverge across countries. This broad pattern is modified by country specificities, with considerable variation in timing and magnitude. Whereas this broad picture emerges for the dynamics, there is much moreuncertainty about the exact levels of inequality in the region. The uncertainty arises from the disparity in estimates for the same country/year combinations, depending on whether they come from household surveys exclusively; from some combination of surveys and administrative tax data; and on whether they attempt to scale income aggregates to achieve consistency with National Accounts estimates. Since no single method is fully convincing at present, we are left with (oftenwide) ranges, or bands, of inequality as our best summaries of inequality levels. Reassuringly, however, the dynamic patterns are generally robust across the bands
Urban infrastructures' maturity and the age(s) of maintenance
No full textInternational audienceThis chapter challenges the idea that infrastructure maturity would be a phase of urban and infrastructural stability. In an increasing number of countries, mainly but not restrictively in the global North, the combination of infrastructure’s ageing and degradation, budgetary constraints and rising environmental issues has gradually shifted professional and public concerns from extension to repair and upkeep. This heralds what the authors coin an ‘age of infrastructure maintenance’, which dramatically contrasts with the modern infrastructural ideal. Drawing from the analysis of French water networks maintenance and asset management practices, this chapter investigates what this age of maintenance concretely encompasses, highlighting two main challenges a maintenance-centred and maturity-focused perspective raises for utilities, namely practices of knowledge production and forms of infrastructures valuation
Response of biogenic secondary organic aerosol formation to anthropogenic NOx emission mitigation
No full textInternational audienceThis study investigates the effects of anthropogenic nitrogen oxide (NOx) mitigation reduction on secondary organic aerosol (SOA) formation from monoterpene and sesquiterpene precursors across Europe, using the three-dimensional (3-D) Chemical Transport Model (CTM) CHIMERE.Two SOA mechanisms of varying complexity are employed: the GENOA-generated Biogenic Mechanism (GBM) and the Hydrophobic/Hydrophilic Organic mechanism (H2O). GBM is a condensed SOA mechanism generated by automatic reduction from near-explicit chemical mechanisms (i.e., the Master Chemical Mechanism - MCM and the peroxy radical autoxidation mechanism - PRAM) using the GENerator of Reduced Organic Aerosol Mechanisms version 2.0 (GENOA v2.0). Conversely, the H2O mechanism is developed primarily based on experimental data, with simplified chemical pathways and SOA formation yields reflecting those from chamber experiments.In the 3-D simulations conducted for the summer of 2018 over Europe, the implementation of GBM significantly improved the model's performance in comparison to simulations using the H2O mechanism, yielding results more consistent with measured aerosol concentrations extracted from the EBAS database.In response to NOx emission mitigation, simulated SOA concentrations increase with GBM but decrease when using the H2O mechanism, unless a highly oxygenated molecules (HOMs) formation scheme is incorporated. The SOA composition becomes more oxidized and concentrations elevate after NOx reduction, particularly in simulations using GBM. These higher concentrations are likely due to enhanced reaction rates of organic peroxy radicals (RO2) with HO2, resulting in more oxidized products from monoterpene degradation that favors HOM formation. The results suggest that detailed SOA mechanisms including autoxidation are necessary for accurate predictions of SOA concentrations in 3-D modeling
ARES VI. Viability of one-dimensional retrieval models for transmission spectroscopy characterization of exo-atmospheres in the era of JWST and Ariel
No full textInternational audienceObserved exoplanet transit spectra are usually retrieved using 1D models to determine atmospheric composition. However, planetary atmospheres are 3D. With the new state-of-the-art James Webb Space Telescope (JWST) and future space telescopes such as Ariel (Atmospheric Remote-sensing Infrared Exoplanet Large-survey), we will be able to obtain increasingly accurate transit spectra. The 3D effects on the spectra will be visible, and we can expect biases in the 1D extractions. In order to elucidate these biases, we have built theoretical observations of transit spectra, from 3D atmospheric modeling through transit modeling to instrument modeling. For this purpose, we used a global climate model (GCM) to simulate the atmosphere, a 3D radiative transfer model to calculate theoretical transmission spectra, and adapted instrument software from JWST and Ariel to reproduce telescope noise. Next, we used a 1D radiative transfer inversion model to retrieve the known input atmosphere and disentangle any biases that might be observed. The study was done from warm planets to ultra-hot planets to assess biases as a function of average planet temperature. Three-dimensional effects are observed to be strongly nonlinear from the coldest to the hottest planets. These effects also depend on the planet’s metallicity and gravity. Considering equilibrium chemistry, 3D effects are observed through very strong variations in certain features of the molecule or very small variations over the whole spectrum. We conclude that we cannot rely on the uncertainty of retrievals at all pressures, and that we must be cautious about the results of retrievals at the top of the atmosphere. However the results are still fairly close to the truth at mid-altitudes (those probed). We also need to be careful with the chemical models used for planetary atmosphere. If the chemistry of one molecule is not correctly described, this will bias all the others, and the retrieved temperature as well. Finally, although tting a wider wavelength range and higher resolution has been shown to increase retrieval accuracy, we show that this could depend on the wavelength range chosen, due to the accuracy on modeling the different features. In any case, 1D retrievals are still correct for the detection of molecules, even in the event of an erroneous abundance retrieval
Contributions historiques de la métropole lyonnaise aux contaminations en microplastiques des sédiments du Rhône
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Zone d’accumulation de déchets plastiques sur les berges de Seine : quid des microplastiques ?
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Sylvain Schoonbaert (coord.), Des ponts et des villes : histoire d'un patrimoine urbain, Mérignac, Ville de Bordeaux et Bordeaux Métropole, 2023, 320p. (compte-rendu)
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Predistribution versus Redistribution: Evidence from France and the United States
No full textInternational audienceWe construct series of posttax income for France over the 1900–2018 period and compare them with US series. We quantify the extent of redistribution—the reduction from pretax to posttax inequality—and estimate the contribution of redistribution in explaining differences in posttax inequality. We find that differences in pretax inequality drive most of the differences in posttax inequality between France and the United States, and that changes over time in both countries are mostly due to changes in pretax inequality. We highlight that the concept of redistribution can be empirically misleading for judging how policies reduce inequalities
Standards, Certification, and Accreditation: Indispensable Tools for European Safety Regulations?
No full textInternational audienceAbstract This chapter shows how standardisation, certification, and accreditation procedures are used for a few decades at the European level for ensuring consumers’ safety against medium-risk products. Despite some regulatory failures, such as in the Medical Devices’ sector, this way of regulating risks is becoming a European model which is both being superimposed on pre-existing older risk regulation regimes and being applied to new domains