Towed sensors and hydrodynamic model evidence the need to include submarine in coastal lagoons water balance, the Mar Menor example (SE Spain).

The use of radionuclide tracers to determine the submarine groundwater discharges has been used widely but in areas highly anthropized as the Mar Menor surface water tributaries can carry high concentration of Radon, making very difficult to distinguish the radionuclide origin. In this paper a combined approach was applied in the Mar Menor, a towed system was designed to enable the continuous measurement of Radon and Nitrate and a hydrodynamic model was used to establish the influence areas of the surface discharge to the lagoon. The areas were Radon was detected and was out from the area located with the model could be establish as a submarine groundwater discharge point.Peer Reviewe

Sedimentation and Fouling of Optical Surfaces at the ANTARES Site

ANTARES is a project leading towards the construction and deployment of a neutrino telescope in the deep Mediterranean Sea. The telescope will use an array of photomultiplier tubes to detect the Cherenkov light emitted by muons resulting from the interaction with matter of high energy neutrinos. In the vicinity of the deployment site the ANTARES collaboration has performed a series of in-situ measurements to study the change in light transmission through glass surfaces during immersions of several months. The average loss of light transmission is estimated to be only ~2% at the equator of a glass sphere one year after deployment. It decreases with increasing zenith angle, and tends to saturate with time. The transmission loss, therefore, is expected to remain small for the several year lifetime of the ANTARES detector whose optical modules are oriented downwards. The measurements were complemented by the analysis of the ^{210}Pb activity profile in sediment cores and the study of biofouling on glass plates. Despite a significant sedimentation rate at the site, in the 0.02 - 0.05 cm.yr^{-1} range, the sediments adhere loosely to the glass surfaces and can be washed off by water currents. Further, fouling by deposits of light-absorbing particulates is only significant for surfaces facing upwards.Comment: 18 pages, 14 figures (pdf), submitted to Astroparticle Physic

Quelles relations entre la mer, les nappes souterraines et les eaux de surface dans le delta du Rhône ?

National audienceLes échanges d'eau sont contrôlés par un système de vannes et pertuis qui relient les étangs à la mer à travers la « Digue à la mer ». Sur la période 1994-2010, les volumes d'eau moyens échangés au niveau du pertuis de la Fourcade sont d'environ 11 millions de m 3 / an d'entrée marine et 20 millions de m 3 /an de sortie vers la mer. Malgré ce système, de grandes variations interannuelles se produisent. En effet, les flux restent dépendants des différences de niveau d'eau de part et d'autre, qui eux dépendent des facteurs environnementaux « internes » (apports d'eau par l'irrigation des rizières) et « externes » : les précipitations et le vent qui influencent le niveau d'eau des étangs, ainsi que les variations du niveau de la mer. Ces variations se produisent à court terme en fonction de la marée et des conditions météorologiques, avec notamment les phénomènes de surcotes marines, et à long terme en relation avec la remontée du niveau de la mer (1 à 7,5 mm/an-voir question 17 : « Changement climatique et surcotes marines, quel avenir pour les plages camarguaises ? »). Les relations entre les eaux souterraines et la mer Il existe une continuité des formations géologiques de part et d'autre du trait de côte permettant des échanges d'eau entre les eaux souterraines et la mer (fig. 1). Les différences de niveau entre la mer et les nappes régissent la direction et l'intensité des flux d'eau. Le bilan de ces flux se produit majoritairement en direction de la mer. Mais il existe néanmoins une intrusion saline, qui explique la salinité plus élevée des eaux de la nappe captive le long de la côte. L'augmentation progressive du niveau de la mer favorise l'intrusion de l'eau de mer dans les terres, ce qui entraînera à plus ou moins long terme une accentuation de la salinisation des eaux. L'eau partout présente en Camargue provient soit de la mer, soit des précipitations, soit de son fleuve. Depuis l'endiguement du Rhône, ce sont essentiellement les canaux d'irrigation et de drainage qui déterminent la distribution de l'eau du fleuve à travers son delta (photo 1). Les eaux continentales souterraines et en surface L'île de Camargue reçoit à la fois des eaux de pluie (470 millions de m 3 /an en moyenne) et des eaux d'irrigation issues du Rhône (296 et 362 millions de m 3 /an pour 1996 et 1993, Fondation Sansouire). En surface, le système lagunaire du Vaccarès est le réceptacle principal des flux hydriques de la zone (photo 2). Dans le sous-sol, on distingue deux types de nappes (fig. 1). Les sédiments récents du Rhône se trouvent sur une épaisseur variant de quelques mètres vers Arles jusqu'à environ 50 m vers le littoral et abritent des nappes plus ou moins connectées et de salinité très variable : douce, salée et même sursalée (jusqu'à 110 g/l, la mer étant à 38 g/l). Au-dessous, une formation de cailloutis grossiers abrite une nappe captive (séparée de la surface par une couche imperméable), dont la salinité augmente progressivement en direction de la mer depuis des eaux presque douces (≈2 g/l au nord) à des eaux de composition marine au sud. Les relations entre les eaux de surface et les eaux souterraines Les échanges d'eau entre la surface et le sous-sol sont complexes et se produisent soit par infiltration d'eau, soit par remontées artésiennes (sous pression). En fonction de l'occupation du sol, les eaux qui s'infiltrent proviennent de l'irrigation des rizières ou de la pluie dans les zones naturelles. Les remontées d'eau vers la surface se produisent quand la pression de l'eau souterraine le permet. On observe ce phénomène là où la topographie est légèrement plus basse, par exemple en bordure nord du Vaccarès où se trouve un forage artésien, mais il est le plus souvent invisible et difficile à quantifier. Ainsi, les étangs de Camargue, et de Vaccarès en particulier, reçoivent une quantité importante d'eau souterraine, estimée à environ un quart des apports de surface. Quelles relations entre la mer, les nappes souterraines et les eaux de surface dans le delta du Rhône

The Rhone River: from large scale geomorphic understanding to sustainable management (channel forms and sediment processes)

International audienc

Modelling of sediment transport pattern in the mouth of the Rhone delta: Role of storm, and flood events

55th Conference of Estuarine-Coastal-Sciences-Association (ECSA), London, ENGLAND, SEP 06-09, 2015International audienceThe delta of the Rhone River is one of the most important in the Mediterranean Sea. Beach erosion problems along its coasts have developed in recent decades, raising the need for a better understanding of the sediment transport processes at the Rhone mouth and the adjacent beaches. Because field data are very difficult to obtain in such an energetic environment, a high-resolution numerical model (Delft3D) is applied to this area. This model is calibrated by taking into account hydrodynamical and morphological observations. Special attention is given to storm and flood events, which are the major morphological drivers. Therefore, scenarios with different wave and flow conditions are run to estimate the influence of these events on the sediment transport. The analysis of historical hydrological data shows that storms from the southeast represent 70% of the events between 1979 to 2010 and that 20% of them were followed by a flood within a few days. Consequently, specific simulations for such conditions are performed using Delft3D. The model simulates trends in the bedload sediment transport that are consistent with the bedforms observed in the bathymetry data. The total sediment transport at the outlet is only influenced by the river flow, but sediment transport at the mouth-bar depends on an equilibrium between the influence of floods and storms and the succession of these events. A period of 2 or 3 days separating the storm and flood peaks is sufficient to differentiate wave and river flow-induced sediment transport. The waves constrain the total transport on the mouth-bar and shallow mouth-lobe and induce a longshore transfer towards the adjacent beaches. The riverine sediments can be exported seaward only if a flood is energetic enough compared to the storm intensity. Regardless, when a flood is greater than the decadal return period (7800 m(3) s(-1)), the sediment is transported from the outlet across the mouth bar and is directed offshore. (C) 2016 Elsevier Ltd. All rights reserved

LA SÉDIMENTATION LAGUNAIRE DES DERNIERS SIÈCLES EN LANGUEDOC-ROUSSILLON. DONNÉES SÉDIMENTOLOGIQUES, ISOTOPIQUES ET PALYNOLOGIQUES

International audienc

A fuzzy classification of the hydrodynamic forcings of the Rhone River plume: an application in case of accidental release of radionuclides

Assessing and modelling the coastal plume dispersion of nuclearized rivers is strategic in case of accidental releases, but taking into account the variation of main hydrodynamic forcings is challenging. This study uses fuzzy c-mean clustering of a 10 years series of discharge and wind speed at the Rhone River estuary (France) in order to explain the variability of its plume. The method allows to classify the data into 6 scenarios of hydrodynamic forcings that were related to different spatial extensions of the plume, as well as to surface currents measured in-situ. These scenarios were used to simulate the extension and dilution of a radioactive release issued from the river. Based on threshold values of the forcings, a decisional tree is proposed to provide a quick decision tool identifying, in real time, which climatological scenario occurs at the river mouth and the potential plume pattern

Unusual Po-210/Pb-210 ratios in the surface water of the Gulf of Lions

Concentrations of Po-210 and Pb-210 have been measured in sea water collected in the Grand Rhone Canyon. Concentrations of Pb-210 are at similar levels to those found in other Mediterranean seawater samples, and are at the levels which would be expected in comparison with global sea water data. The same applies to the Po-210 concentrations in samples from below 100 m depth. Surface samples from above 100 m have Po-210 at levels rather higher than expected, and their Po-210/Pb-210 ratios are about 1 or more as compared with the usual open ocean ratio of about 0.5. These data can be interpreted as indicating another source of supply of Po-210 to the surface layer in addition to the normal atmospheric input. We suggest that an episodic advective particulate input, probably originating in the output of the Rhone river and perhaps involving resuspension of fine particulates from the bottom sediments as a result of storm conditions, is the most likely candidate for this additional source.Les activités en 210Po et 210Pb total ont été mesurées dans la colonne d'eau du canyon du Grand Rhône, sur la marge continentale du Golfe du Lion. Les activités en 210Pb sont similaires à celles précédemment estimées pour les eaux méditerranéennes et présentent des valeurs attendues par comparaison avec les autres océans. Il en est de même pour les activités en 210Po au-dessous de 100 m de profondeur. En revanche, entre 0 et 100 m, le 210Po atteint des valeurs beaucoup plus élevées que celles généralement observées, et le rapport Full-size image (<1 K) est égal ou supérieur à 1, très différent de celui de l'océan d'environ 0,5. Ces données impliquent l'existence d'une source supplémentaire de 210Po, autre que les retombées atmosphériques. Nous suggérons que celle source résulte d'un apport advectif et épisodique de particules, probablement originaire du Rhône et peut-être de la resuspension de sédiment sur le plateau ou le haut de pente à la suite d'une tempête

Cs and

Various studies have been conducted during the fast decade onto atmospheric deposited 210Pb and caesium isotopes in soils in order to quantify soil erosion rates. In North Morocco (Tangier area), erosion is a real problem leading to silting up of artificial lakes. Soil profiles were collected in cultivated areas from the catchment basin of one of this lake in order to quantify the erosion. 137Cs and 210Pb concentrations and inventories were measured and their spatial distribution was studied in relation with other parameters : granulometry, pH, organic matter content. Mean 137Cs inventory in stable soils was found to be 2582 Bq.m-2 in 1999, in agreement with literature data for Spanish and Portuguese soils. Depth profiles were usual, showing an exponential decrease with depth for 210Pb and a subsurface peak for 137Cs in reference soils where it was found until 30 cm depth. No clear relations appeared with organic matter content or pH and the distribution of the inventories is probably linked to erosion process. Estimated erosion rates varied from 5 to 66 t.ha-1y-1, but the use of different models for such estimation led to important differences

Kd distributions in freshwater systems as a function of material type, mass-volume ratio, dissolved organic carbon and pH

International audienceThe contamination of freshwater systems by metals is a worldwide problem due to their toxicity, abundance and persistence in the environment. One of the main processes affecting their residence time in freshwater systems is their solid-liquid fractionation, often modeled by the Kd approach defined as the concentration ratio between the particulate and dissolved phases under the assumptions of reversibility, equilibrium and trace conditions. Because Kd is an empirical parameter that depends on several environmental factors, its variability can cover orders of magnitude for a single element. Such variability is unknown for most case studies, but the modelers need it to evaluate the uncertainty of their calculations. In order to fill this gap, this paper presents statistical Kd distributions for in situ suspended matters as a function of suspended load, dissolved organic carbon and pH. They were obtained using a database containing 8564 Kd values from 50 elements, classified as a function of three exchange conditions (adsorption, desorption and in situ) and two environmental components (suspended and deposited sediments). These distributions and relations can be used to reduce of several order of magnitudes the global variability of Kd values in the case where in situ data are not available. © 201