Liquid chromatography/mass spectrometry stable isotope analysis of dissolved organic carbon in stream and soil waters

International audienceA commercial interface coupling liquid chromatography (LC) to a continuous-flow isotope ratio mass spectrometry (CF-IRMS) instrument was used to determine the d13C of dissolved organic carbon (DOC) in natural waters. Stream and soil waters from a farmland plot in a hedgerow landscape were studied. Based on wet chemical oxidation of dissolved organics the LC/IRMS interface allows the on-line injection of small volumes of water samples, an oxidation reaction to produce CO2 and gas transfer to the isotope ratio mass spectrometer. In flow injection analysis (FIA) mode, bulk DOC d13C analysis was performed on aqueous samples of up to 100 mL in volume in the range of DOC concentration in fresh waters (1-10 mg C.L-1). Mapping the DOC d13C spatial distribution at the plot scale was made possible by this fairly quick method (10 min for triplicate analyses) with little sample manipulation. The relative contributions of different plot sectors to the DOC pool in the stream draining the plot were tentatively inferred on the basis of d13C differences between the hydrophilic and hydrophobic components. Copyright © 2011 John Wiley & Sons, Ltd

Contribution à la connaissance de la topographie et de l'hydrologie des cavités noyées du bouillon (Source du Loiret) Années 2000-2001

Rapport : SSL - ADRAPILSL'association Spéléologie Subaquatique Loiret, dont le siège social est situé à l'Université d'Orléans, s'est formée en 1999 avec pour objectif la poursuite de l'exploration des cavités noyées du Val d'Orléans et en particulier des sources du Loiret, avec des moyens accrus, grâce à une meilleure collaboration entre les plongeurs spéléo d'Orléans et des scientifiques de l'Université. Pour être réalisé, cet objectif nécessite une aide financière soutenue des collectivités locales pour ce qui concerne l'acquisition de matériels de plongée performants, indispensables à la conduite d'explorations longues en milieu souterrain. En 2000 nous avons sollicité l'aide de l'ADAPRILS, ainsi que de plusieurs entreprises ou collectivités (Lyonnaise des Eaux, Mairie d'Orléans, ASRL, Parc Floral) afin de pallier aux grandes difficultés que nous connaissions alors pour gonfler les bouteilles de plongée. Les subventions accordées en 2000 nous ont permis d'acquérir un compresseur adapté à nos besoins et d'assurer ainsi la poursuite de notre activité. Le présent rapport fait état des connaissances nouvelles sur le cheminement des drains et la circulation des eaux, apportées aussi bien par l'exploration directe que par des opérations de traçages par coloration réalisées en plongée à partir de la source du Bouillon

Les trois pertes-émergences (ou inversacs) du domaine de la Source (Loiret)

Le val d'Orléans combine des caractéristiques fluviales évidentes à un fonctionnement karstique. Les cours d'eau de surface contribuent de manière importante à la recharge de l'aquifère. D'abord, en amont d'Orléans, au contact du lit de la Loire dont les pertes de débit enregistrées à partir de Sully sur Loire (http://www2.centre.ecologie.gouv.fr/SIEL) témoignent de l'importance du phénomène. En second, au niveau des petits cours d'eau drainant le val, la forêt d'Orléans ou la Sologne, à leur passage des terrains imperméables aux calcaires. Les principaux points d'émergence d'eau souterraine du système sont eux-mêmes directement influencés par le régime des eaux de surface, soit qu'ils se situent dans le lit même du fleuve (en aval d'Orléans) ou d'autres cours d'eau comme le Dhuy ou le Loiret, soit qu'ils se trouvent temporairement submergés par les écoulements de surface. Ces caractéristiques peuvent entrainer une variabilité importante du système à différentes échelles; à court terme ainsi que de manière saisonnière en fonction de la pluviométrie locale et du régime de la Loire, mais aussi à plus long terme par exemple en fonction de l'évolution de l'enfoncement du lit de la Loire. Dans les systèmes fluvio-karstiques, jugés instables, de petites variations du partage entre écoulement de surface et écoulement souterrain, diffus ou canalisés, sont tenues pour responsables de modifications géomorphologiques importantes et durables (1). Cet article, écrit à l'occasion du colloque tenu à la mémoire de Michel Lepiller, retrace différents travaux récents sur le fonctionnement des sources karstiques situées dans l'enceinte de l'ancien domaine de la Source, et connues comme la (les) source(s) de la rivière Loiret. Situés dans un territoire profondément modelé par l'homme, les points d'émergence des sources du Loiret et le cours du Loiret lui même ont été à plusieurs reprises aménagés, particulièrement en ce qui concerne la relation entre écoulement de surface et émergence d'eau souterraine. Les documents les plus instructifs à ce sujet sont sans doute l'article rédigé en 1736 par l'abbé de Fontenu et les plans de Beaurain réalisés en 1739 et publiés ensemble dans les Mémoires de l'Académie Royale des Inscriptions et Belles Lettres (2). Le point important concerne l'écartement progressif du cours du Dhuy des points d'émergence karstique donnant naissance au Loiret (Figure 1). Outre l'attrait architectural apporté par ces aménagements, l'isolement des points d'émergence a créé des conditions privilégiées pour le prélèvement et accessoirement l'analyse des eaux résurgentes

L'inversac (perte-émergence) de la résurgence du Bouillon (source du Loiret, France).

Le fonctionnement en perte de la source du Loiret est contrôlé par les hauteurs d'eau de la Loire et de la rivière le Dhuy suivant une relation du type : HDhuy = e (2 + 0.05 HLoire) + 63

River backflooding into a karst resurgence (Loiret, France).

The group of springs located in the west part of the Val d'Orléans exemplifies a type of karstic emergence which has the particularity to get most of its recharge water from a single surface water source, which in this particular case is the River Loire. Hence the flow of this group of springs is known to fluctuate in a close relationship with the water level of the River Loire. Since the second half of the 1990s, the conduit of the upstream spring of the Loiret river (so-called Le Bouillon) has been periodically seen to be invaded by the turbid waters of a small surface tributary (Le Dhuy) flowing back from the confluence to the spring, which then functioned as a swallow-hole. Plotted in a Dhuy versus River Loire diagram, stages of backflooding days describe a domain limited by a curve of the form HDhuy=c+e(aHLoire+b). The exponential form of the relation corresponds to the increasing resistance of the emerging flow of the spring to the backflooding of the tributary waters, as the River Loire stages rise. The equation above was used to compute a daily backflow index enabling the effective reconstruction of all occurrences effectively counted during the regular period of observation of the spring. Extended to 1985, one can observe that the early 1990s do not appear as a favorable period to backflow events but some may have occurred during the years 1986 to 1989. The observation of rainfall intensity preceding backflooding shows that in a short time span there is no necessity to evoke intrinsic changes inside the Val d'Orléans basin to explain what might appear as a troublesome new phenomenon. In conclusion backflooding has probably existed for a long time and is simply under the control of local heavy rainfall during low River Loire stages

Laghi di Monticchio (Southern Italy, Region Basilicata): genesis of sediments—a geochemical study

International audienceThe sedimentation record of Lago Grande di Monticchio (LGM) is one of the most prominent paleoclimatic archives in the on-glaciated areas of Europe. However, the modern lake system has never been the subject of intense limnological studies. On the basis of hydrochemical water profiles, detailed investigations of sediment short cores and in situ pore water profiles from the littoral to the profundal zone, we elucidate spatial variations of sediment genesis within the lake basin and the importance of various depth sections for the lake's internal nutrient cycling. Sediments from the smaller meromictic Lago Piccolo di Montichio are discussed as a reference. Our study demonstrates: (i) distinctly higher sediment accumulation for the centre of the lake basin by focussing of the settling particle flux; (ii) decline of carbonate from the littoral to the profundal zones; (iii) nonsynchronous change of calcite net-accumulation for various water depths; (iv) exceptionally high cation release from sediments covering the steeply inclining sector of the lake basin; (v) relatively constant dissolved silica concentrations in the pore waters (SiO2 *42 mg/l) independent of water depth and sediment composition; (vi) influx of oxygen-bearing groundwater into the anoxic hypolimnion after heavy rainfall and the associated precipitation of Fe-oxihydroxides; (vii) higher release of NH4 by anaerobic degradation of organic matter at a water depth of 23 m than for sediments at a maximum water depth of 32 m, whereby the latter reflects the importance of seasonal sediment re-oxidation for anaerobic degradation of organic debris; (viii) although seasonal reoxidation of sediments from various water depths is quite different, Oxygen Index values of LGM sediments fall in a small range, which reflects rapid microbial consumption of seasonally re-generated easily bio-degradable organic molecules

Oxidation of organic matter in a karstic hydrologic unit supplied through stream sinks (Loiret, France)

The aim of this paper is to appraise the ability of the oxidation of riverine organic matter in the control of limestone dissolution, in a karst network. Biogeochemical processes during infiltration of river water into an alluvial aquifer have already been described for an average flow velocity of 4-5 m d−1 (Jacobs, L. A., von Gunten, H. R., Keil, R. and Kuslys, M. (1988) Geochemical changes along a river-groundwater infiltration flow path: Glattfelden, Switzerland. Geochim. Cosmochim. Acta 52, 2693-2706; Von Gunten, H. R., Karametaxas, G., Krähenbühl, U., Kuslys, M., Giovanoli R., Hoehn E. and Keil R. (1991) Seasonal biogeochemical cycles in riverborne groundwater. Geochim. Cosmochim. Acta 55, 3597-3609; Bourg, A. C. M. and Bertin, C. (1993) Quantitative appraisal of biogeochemical processes during the infiltration of river water into an alluvial aquifer. Environ. Sci. Technol. 27, 661-666). Karstic drainage networks, such as in the river Loire-Val d'Orléans hydrologic system (Fig. 1), make possible flow velocities up to 200 m h−1 and provide convenient access to different water samples several tens of km apart, at both extremities of the hydrologic unit (Chéry, J.-L. (1983) Etude hydrochimique d'un aquifère karstique alimenté par perte de cours d'eau (la Loire): Le système des calcaires de Beauce sous le val d'Orléans. Thèse, Université d'Orléans; Livrozet, E. (1984) Influence des apports de la Loire sur la qualité bactériologique et chimique de l'aquifère karstique du val d'Orléans. Thèse, Université d'Orléans). Recharge of the karstic aquifer occurs principally from influent waters from stream sinks, either through coarse alluvial deposits or directly from outcrops of the regional limestone bedrock (Calcaires de Beauce). Recharge by seepage waters from the local catchment basin is small (Zunino, C., Bonnet, M. and Lelong, F. (1980) Le Val d'Orléans: un exemple d'aquifère à alimentation latérale. C. R. somm. Soc. Géol. Fr. 5, 195-199; Gonzalez R. (1992) Etude de l'organisation et évaluation des échanges entre la Loire moyenne et l'aquifère des calcaires de Beauce. Thèse, Université d'Orléans) and negligible in summer. This karstic hydrologic system is the largest in France in terms of flow (tens to hundreds of m3/s) and provides the main water resource of the city of Orléans. Chemical compositions of influent waters (River Loire) and effluent waters (spring of the river Loiret) were compared, in particular during floods in summer 1992 and 1993 (Figs 2-4). Variation of chloride in the River Loire during the stream rise can be used as an environmental tracer of the underground flow (Fig. 2). Short transit times of about 3 days are detectable (Fig. 2) which are consistent with earlier estimations obtained with chemical tracers (Ref. in Chéry, J.-L. (1983) Thèse, Université d'Orléans). Depending on the hydrological regime of the river, organic carbon discharge ranges between 3-7 and 2-13 mg/l for dissolved and particulate matter respectively (Fig. 3). Eutrophic characteristics and high algal biomasses are found in the River Loire during low water (Lair, N. and Sargos, D. (1993) A 10 year study at four sites of the middle course of the River Loire. I -- Patterns of change in hydrological, physical and chemical variables in relation to algal biomass. Hydroécol. Appl. 5, 1-27) together with more organic carbon rich suspended particulate matter than during floods (30-40 Corg % dry weight versus 5-10%). Amounts of total organic carbon and dissolved oxygen (Fig. 3) dramatically decrease during the underground transport, whereas conversely, dissolved calcium, alkalinity and inorganic carbon increase (Fig. 4). Anoxia of outflows may start in April. Dissolution of calcium carbonates along the influent path outweighs closed system calcite equilibrium of inflow river waters (Table 3). The impact of organic matter oxidation on calcite dissolution may be traced by variations of alkalinity and total carbonates in water. Following, Jacobs, L. A., von Gunten, H. R., Keil, R. and Kuslys, M. (1988) Geochemical changes along a river-groundwater infiltration flow path: Glattfelden, Switzerland. Geochim. Cosmochim. Acta 52, 2693-2706), results are shown graphically (Fig. 5). Extent of reactions is controlled by the consumption of dissolved O2 and nitrate for organic matter oxidation and by the release of Ca2+ for calcite dissolution (Table 2). The karstic network is considered to behave like a biological reactor not exchanging with the atmosphere, with steady inhabitant microbial communities (Mariotti A., Landreau A. and Simon B. (1988) 15N isotope biogeochemistry and natural denitrification process in groundwater: Application to the chalk aquifer of northern France. Geochim. Cosmochim. Acta 52, 1869-1878; Gounot, A.-M. (1991) Ecologie microbienne des eaux et des sédiments souterrains. Hydrogéologie, 239-248). Thus, energy requirements only are considered, not carbon assimilation. Moreover, there is no necessity to invoke any delay for nitrification enhancement, as observed elsewhere, after waste water discharge into the river (Chesterikoff, A., Garban, B., Billen, G. and Poulin, M. (1992) Inorganic nitrogen dynamics in the River Seine downstream from Paris (France). Biogeochem. 17, 147-164). 05n microbial processes are assumed to be aerobic respiration, nitrification and denitrification. Reactions with iron and manganese, real but not quantitatively important, were neglected. Sulphate reduction and methane formation, certainly not active, were not considered. Denitrification, which is suggested by low nitrate and ammonium concentrations and anoxia in the outflow, is known to be rapid enough to be achieved in a short time (Dupain, S. (1992) Dénitrification biologique hétérotrophe appliquée au traitement des eaux d'alimentation: Conditions de fonctionnement et mise au point d'un procédé. Thèse, Université Claude Bernard, Lyon). Reaction are somewhat arbitrary but conform to general acceptance (Morel, M. M. and Hering, J. G. (1993) Principles and Applications of Aquatic Chemistry. Wiley, New York). Anaerobic ammonium oxidation (Mulder A., van de Graaf, A. A., Robertson, L. A. and Kuenen, J. G. (1995) Anaerobic ammonium oxidation discovered in a denitrifying fluidized bed reactor. FEMS Microbiol. Ecol. 16, 177-184), although possible, was not considered. In fact, C/N ratio of the reactive organic matter has only mild repercussions on the results; i.e. in the same range as the analytical errors for alkalinity and total carbonates. The objective was simply to roughly confront characteristics of outflowing waters and the calculation. Respective roles of aerobes and denitrifiers, for instance, are not certain. Several periods during low water or floods were selected with various ranges for calcium dissolution or nitrate and oxygen concentrations. The result is that in most cases simulation and data are in reasonable accordance (Fig. 5). Amounts of organic matter in River Loire are generally sufficient to sustain the process (Table 3). Particulate organic matter is probably the most reactive. The balance of oxidation of organic matter indicates that about 65 μg Corg/l*h are oxidized during the transport without much variation with the river regime or organic discharge. It is concluded that limestone dissolution is directly dependent on organic matter oxidation, but variation occurs (7-29 mg CaCO3/l) with the level of bases that can be neutralized in the influent River Loire water

Modalité d'infiltration dans le sol de carbone et de matière organique d'origine routière dans un bassin d'eau pluviale absorbant.

Le lessivage des routes par les eaux pluviales peut apporter à l'environnement des quantités importantes de matière organique produites par la circulation automobile (1, 2). Le long des grandes voies de circulation des bassins d'orage atténuent en général la charge polluante des eaux avant leur retour aux cours d'eau. En région calcaire les bassins sont cependant le plus souvent absorbants, les eaux pluviales rejoignant la nappe phréatique rapidement en s'infiltrant à travers le sol (3). Dans cette étude préliminaire nous avons cherché à évaluer le comportement de la charge organique dissoute des eaux pluviales de routes lors de l'infiltration dans une zone d'effondrement karstique. La charge organique a été quantifiée par dosage du carbone organique dissous (COD) et mesure de l'intensité de fluorescence dans les échantillons bruts et dans des fractions obtenues par ultrafiltration tangentielle ou par chromatographie sur résines polymériques hydrophobes (XAD8). La présence de nanoparticules de carbone dans ces échantillons a été recherchée par microscopie électronique à transmission (MET) (4)

Acide diaminopimélique libre des bivalves symbiotiques Free diaminopimelic acid in symbiotic bivalves

International audienceL'analyse de la composition en acides aminés libres des tissus de plusieurs bivalves symbiotiques provenant des sites hydrothermaux sous-marins des Galapagos, de la fosse du Japon ou du prisme d'accrétion de la Barbade montre la présence de quantités parfois très importantes d'acide diaminopimélique. Ce composé d'origine bactérienne témoigne de la présence des bactéries symbiontes et des échanges entre l'hôte et les bactéries. Les différences notées entre les espèces de bivalves peuvent refléter à la fois la variation taxinomique entre les souches bactériennes, et la nature ou l'intensité différente des échanges bactéries-hôte. La variation entre les individus peut refléter les différences micro-environnementales affectant l'état physiologique des bivalves. Free amino acids were analyzed in tissues of symbiotic bivalves from hydrothermal vent sites at Galapagos Rift, and cold-seeps in Japan trench and Barbados subduction area. Diaminopimelic acid (a fragment of the bacterial cell wall mureid complex) is, in some cases, one of the most abundant compounds. It's presence in the tissues of the bivalves is related to exchanges between host and symbionts. Diaminopimelate concentration differences among species may correspond to both taxonomic bacterial differences and different carbon translocation processes from bacteria to host. Variation among individuals may correspond to fluctuation of micro-environmental conditions

Pore-water chemistry in mangrove sediments: relationship with species composition and developmental stages. (French Guiana).

Spatial and seasonal variability of sedimentary salinity, pH, redox potential and solid phase sulphide concentration were investigated in a range of mangrove communities along the coast of French Guiana. Seasonal depth distributions of these parameters and organic content were compared within Avicennia, Rhizophora and mixed mangrove stands at different stages of plant development. Mangrove communities and variable surface water inputs strongly impact sediment and ground water properties. In the upper sediment, changes in salinity are mainly controlled by seasonal conditions, transpiration and proximity of fresh water influx, whereas we suggest that constant basal salinity results from an accumulation of salt that has migrated as a result of density driven convection processes. There are no clear differences between the depth distributions of salinity obtained beneath Avicennia germinans and Rhizophora mangle stands, implying that plant zonations are not primarily controlled by soil salinity in this environment. Nevertheless, R. mangle grows in places subjected to the greatest variability in freshwater influxes, suggesting that Rhizophora might require or withstand occasional inundation by fresh water. Beneath Rhizophora stands, sediment properties reflect anaerobic and sulphidic conditions close to the sediment surface. In contrast, beneath Avicennia stands, sediment geochemistry mostly depends on the stages in forest development, on contents in sedimentary organic matter and on seasonal changes. In the early stage of Avicennia settlement, the sediment at the level of radial, pneumatophore-bearing cable roots, displays permanent suboxic conditions with Eh values reaching 400 mV. These high Ehs are interpreted as an effect of the oxidation produced by the cable root system. The development of mature Avicennia stands results in accumulation of sedimentary organic matter and promotes low Ehs and the reduction of pore-water sulphate. Near cable root level, the oxidation process observed in pioneer mangroves results in a reoxidation of solid sulphides produced previously. During dry conditions, the desiccation of the upper sediment adds its oxidation effects to those of root activity. As a result, suboxic processes dominate in the upper, 20-cm-thick layer; organic matter decomposition and sulphur oxidation strongly acidify the sediment. Below 20 cm, the sediment is anaerobic and sulphidic. Hence, sulphide concentrations depend on the edaphic conditions controlling decay processes and appear to be a consequence rather than a cause of the observed zonation of vegetal species. The small size of A. germinans propagules might have a significant influence on the extensive development of this plant community along the highly dynamic coastline of the Guianas. This study demonstrates that the different properties of pore-water were intimately linked and that the explanation of the evolution of this forest reflects a combination of multiple parameters. Moreover, it appeared that the organic content played a key role along with the species composition and the seasonal variations (waterlogging, desiccation)