An Analysis of Turbulent Heat Fluxes and the Energy Balance During the REFLEX Campaign

Three eddy covariance stations were installed at the Barrax experimental farm during the Land-Atmosphere Exchanges (REFLEX) airborne training and measurement campaign to provide ground truth data of energy balance fluxes and vertical temperature and wind profiles. The energy balance closure ratio (EBR) was 105% for a homogeneous camelina site, 86% at a sparse reforestation site, and 73% for a vineyard. We hypothesize that the lower closure in the last site was related to the limited fetch. Incorporating a vertical gradient of soil thermal properties decreased the RMSE of the energy balance at the camelina site by 16 W m^?2. At the camelina site, eddy covariance estimates of sensible and latent heat fluxes could be reproduced well using mean vertical profiles of wind and temperature, provided that the Monin—Obukhov length is known. Measured surface temperature and sensible heat fluxes suggested high excess resistance for heat (kB^?1 = 17).     

La méthode SHYREG débit—application sur 1605 bassins versants en France métropolitaine

Résumé

La méthode SHYREG est une approche développée pour la connaissance régionale de l’aléa pluvial (SHYREG pluie) et hydrologique (SHYREG débit) en tout point du territoire français. Elle est basée sur le couplage d’un générateur stochastique de pluie horaire et d’un modèle hydrologique. Cet article présente les résultats de la mise en ?uvre de la méthode sur 1605 bassins versants répartis sur la France métropolitaine. Sur les fréquences courantes (c.à.d. périodes de retour inférieures à 10 ans), la méthode restitue correctement les quantiles de débit de crue ajustés à une loi statistique sur les observations (loi GEV, selon le critère de Nash-Sutcliffe). Plusieurs critères sont utilisés pour valider l’extrapolation des débits à des fréquences extrêmes: (a) en la confrontant à de longues chroniques de débits observés, (b) en analysant dans le modèle hydrologique la saturation du réservoir de production synonyme de comportement asymptotique avec les pluies, et (c) en étudiant la stabilité de la méthode à travers les critères statistiques.

Editeur Z.W. Kundzewicz; Editeur associé G. Mahé

Citation Aubert, Y., Arnaud, P., Ribstein, P., et Fine, J.-A., 2014. La méthode SHYREG débit, application sur 1605 bassins versants en France Métropolitaine. Hydrological Sciences Journal, 59 (5), 993–1005.     

Ardières-Morcille in the Beaujolais,France: A research catchment dedicated to study of the transport and impacts of diffuse agricultural pollution in rivers

The 8-km² Morcille catchment, which is a sub-catchment of the 150-km² Ardières catchment in the Beaujolais region of France, is one of the first sites in Europe where research has been conducted on surface water contamination by pesticides. A consolidated hydrological and chemical dataset has been set up with data collected since 2002 on the Morcille River and since 2011 on the Ardières River. Additional data on the ecotoxicological and ecological impacts of pesticides on aquatic microbial communities and macroinvertebrates has also been recorded in both rivers since 2005. The ‘Site Atelier Ardières-Morcille Dataset’ described here combines rainfall and stream water height measurements at gauged stations with concentrations of two trace elements and nine pesticides (mainly herbicides, fungicides and some of their metabolites) in both the Ardières and Morcille rivers. All contaminant concentration data showed spatial and temporal variability in water quality associated with pesticide use and rainfall patterns. This long-term monitoring framework made it possible to estimate the persistence of two herbicides (diuron and norflurazon) after legislation banning them. It took 4 years for diuron and more than 10 years for norflurazon concentrations to fall below 0.1 μg/L. Concurrent biological data showed a gradient of impacts consistent with chemical anthropogenic pressure, and rapid recovery of phototrophic microbial communities after the diuron ban. Finally, monitoring data on pesticide transport in a grassed strip set on a slope of the Morcille catchment confirmed that vegetative filter strips can effectively reduce diuron fluxes in surface runoff (>80% abatement) and infiltration water (>70% abatement). The full dataset offers a valuable resource for the validation of hydrological models and the development of global approaches to better understand the pressure–transport–exposure–impact chain and aquatic community resilience at the small catchment scale.     

Variations in the response of the dune coast of northern France to major storms as a function of available beach sediment volume

A series of airborne topographic LiDAR data were obtained from May 2008 to January 2014 over two coastal sites of northern France (Bay of Wissant and east of Dunkirk). These data were used with wind and tide gauge measurements to assess the impacts of storms on beaches and coastal dunes, and particularly of the series of major storms that hit western Europe during the fall and early winter of 2013. Our results show a high variability in shoreline response from one site to the other, but also within each coastal site. Coastal dune erosion and shoreline retreat occurred at both sites, particularly on the coast of the Bay of Wissant where shoreline retreat up to about 40 m was measured. However, stability or even shoreline advance were also observed despite the occurrence of an extreme water level with a return period >100 years during the storm Xaver in early December 2013. Comparison of shoreline change with variations of coastal dune and upper beach volumes revealed only weak relationships. Our results nevertheless showed that shoreline behavior seems to strongly depend on the initial sediment volume on the upper beach before the occurrence of the storms. According to our measurements, an upper beach volume of about 30 m³ m^?1 between the dune toe and the mean high water level is sufficient at these sites to protect the coastal dunes from storm waves associated with high water levels with return periods >10 years. The identification of such thresholds in terms of upper beach width or sediment volume may represent valuable information for improving the management of shoreline change by providing an estimate of the minimum quantity of sand on the upper beach necessary to ensure shoreline stability in this region. Copyright © 2016 John Wiley & Sons, Ltd.     

Did tillage erosion play a role in millennial scale landscape development?

Landscape evolution models (LEMs) quantitatively simulate processes of sedimentation and erosion on millennial timescales. An important aspect of human impact on erosion is sediment redistribution due to agriculture, referred to herein as tillage erosion. In this study we aim to analyse the potential contribution of tillage erosion to landscape development using LEM LAPSUS. The model is calibrated separately for a water erosion process (i) without tillage and (ii) with tillage. The model is applied to the ~250 km² Torrealvilla case study catchment, SE Spain. We were able to simulate alternating sequences of incision and aggradation, that are important on longer (millennial) timescales. Generally, model results show that tillage erosion adds to deposition in the lower floodplain area, but neither water erosion alone nor water with tillage erosion together could exactly reproduce the observed amounts of erosion and sedimentation for the case study area. In addition, scale effects are apparent. On hillslopes, tillage may contribute importantly to erosion and may fill local depressions. If assessed on the catchment scale, sediments from tillage erosion eventually reach the lower floodplain area where they contribute to deposition. However, water erosion was observed in the model simulations to be the most important process on the catchment scale. This is the first time that tillage erosion has been explicitly included in a landscape evolution model at a millennial timescale and large catchment scale. Copyright © 2012 John Wiley & Sons, Ltd.     

In situ record of sedimentary processes near the Rhône River mouth during winter events (Gulf of Lions,Mediterranean Sea)

The environment is impacted by natural and anthropogenic disturbances that occur at different spatial and temporal scales, and that lead to major changes and even disequilibria when exceeding the resiliency capacities of the ecosystem. With an annual mean flow of 1700 m³ s⁻¹, the Rhône River is the largest of the western Mediterranean basin. Its annual solid discharges vary between 2 and 20 Mt, with flood events responsible for more than 70% of these amounts.     

Global optimization of core station networks for space geodesy: application to the referencing of the SLR EOP with respect to ITRF

We apply global optimization in order to optimize the referencing (and consequently the stability) of the Earth Orientation Parameters (EOP) with respect to ITRF2005. These EOP are derived at a daily sampling from SLR data, simultaneously with weekly station positions. The EOP referencing is carried out with minimum constraints applied weekly to the three rotations and over core station networks. Our approach is based on a multi objective genetic algorithm, a particular stochastic global optimization method, the reference system effects being the objectives to minimize. We thus use rigorous criteria for the optimal weekly core station selection. The results evidence an improvement of 10% of the stability for Polar Motion (PM) series in comparison to the results obtained with the network specially designed for EOP referencing by the Analysis Working Group of the International Laser Ranging Service. This improvement of nearly 25 μas represents 50% of the current precision of the IERS 05 C04 PM reference series. We also test the possibility of averaging the weekly networks provided by our algorithm (the Genetically Modified Networks—GMN) over the whole time period. Although the dynamical nature of the GMN is clearly a key point of their success, we can derive such a global mean core network, which could be useful for practical applications regarding EOP referencing. Using this latter core network moreover provides more stable EOP series than the conventional network does.     

Genesis and soil environmental implications of intact in-situ rhizoliths in dunes of the Badain Jaran Desert,northwestern China

Acta Geochimica - Desert rhizoliths are generally found as weathered, broken and scattered samples on dune field surface, but rarely in-situ in their initial states buried under the soil of desert...