Spatial and Temporal Variability of Benthic Respiration in a Scottish Sea Loch Impacted by Fish Farming: A Combination of In Situ Techniques     

Cécile Cathalot  Bruno Lansard  Per O. J. Hall  Anders Tengberg  Elin Almroth-Rosell  Anna Apler  Lois Calder  Elanor Bell  Christophe Rabouille 《Aquatic Geochemistry》2012,18(6):515-541

The effects of fish farm activities on sediment biogeochemistry were investigated in Loch Creran (Western Scotland) from March to October 2006. Sediment oxygen uptake rates (SOU) were estimated along an organic matter gradient generated from an Atlantic salmon farm using a combination of in situ techniques: microelectrodes, planar optode and benthic chamber incubations. Sulphide (H₂S) and pH distributions in sediment porewater were also measured using in situ microelectrodes, and dissolved inorganic carbon (DIC) fluxes were measured in situ using benthic chambers. Relationships between benthic fluxes, vertical distribution of oxidants and reduced compounds in the sediment were examined as well as bacterial abundance and biomass. Seasonal variations in SOU were relatively low and mainly driven by seasonal temperature variations. The effect of the fish farm on sediment oxygen uptake rate was clearly identified by higher total and diffusive oxygen uptake rates (TOU and DOU, respectively) on impacted stations (TOU: 70 ± 25 mmol O₂ m^?2 day^?1; DOU: 70 ± 32 mmol O₂ m^?2 day^?1 recalculated at the summer temperature), compared with the reference station (TOU: 28.3 ± 5.5 mmol O₂ m^?2 day^?1; DOU: 21.5 ± 4.5 mmol O₂ m^?2 day^?1). At the impacted stations, planar optode images displayed high centimetre scale heterogeneity in oxygen distribution underlining the control of oxygen dynamics by small-scale processes. The organic carbon enrichment led to enhanced sulphate reduction as demonstrated by large vertical H₂S concentration gradients in the porewater (from 0 to 1,000 μM in the top 3 cm) at the most impacted site. The impact on ecosystem functions such as bioirrigation was evidenced by a decreasing TOU/DOU ratio, from 1.7 in the non-impacted sediments to 1 in the impacted zone. This trend was related to a shift in the macrofaunal assemblage and an increase in sediment bacterial population. The turnover time of the organic load of the sediment was estimated to be over 6 years.  相似文献   

Hydrogen and Oxygen Isotope Reference Materials for the Analysis of Water Inclusions in Halite     

Thomas Rigaudier  Véronique Gardien  François Martineau  Ghislaine Reverdy  Christophe Lécuyer 《Geostandards and Geoanalytical Research》2012,36(1):51-59

Fluid inclusions represent a unique opportunity for a straightforward determination of the chemical and isotopic composition of fluids that composed the hydrosphere and atmosphere over Earth’s history. The production of reference materials in the laboratory is needed to monitor and to validate the determination of hydrogen and oxygen isotope compositions of water inclusions. We propose a protocol leading to the experimental synthesis of halite crystals that contain water inclusions whose δD and δ¹⁸O values can be related to those of surrounding evaporating waters where the crystals grew. Corrections to isotopic measurements were performed by applying an orthogonal projection of the raw data to the water evaporation trajectory line whose slope can be predicted by taking into account the parameters developed in the linear resistance model of Craig and Gordon (1965). Several hundreds of grams of halite reference material can be produced rapidly (within 2 d) at a low cost and can be stored within a vacuum desiccator at ambient temperature over several months or years. The described method is especially useful for the analysis of anhydrous salts and the interpretation of isotopic fractionations that operate within the surficial water cycle.  相似文献   

A study of celestine equilibrium in marine sediments using the entire ODP/IODP porewater data base     

Guilhem Hoareau  Christophe Monnin  Francis Odonne 《Geochimica et cosmochimica acta》2010,74(14):3925-2663

The stability of celestine (SrSO₄) in marine sediments has been investigated through the calculation of its saturation index at the in situ temperature and pressure, using the entire ODP/IODP porewater composition data base (14,416 samples recovered from sediments collected during 95 ODP and IODP Legs) that has been thoroughly corrected for missing data and inconsistencies. The porewater in situ pressure has been obtained from depth data, and the in situ sample temperature has been calculated from the bottom seawater temperature and from the measured thermal gradient. When the latter is unavailable, a default value of 35 °C/km or an assumed gradient similar to that of a site located close to the study area has been used. Molarities have been converted to molalities through the calculation of the porewater densities, which have represented by an empirical function of the total dissolved solids load up to 150 g/L.Ocean bottom waters are largely undersaturated with respect to celestine. Yet sediment porewater saturation is not uncommon: it is reached in 83 boreholes (i.e. about 10% of all boreholes) drilled during 22 ODP/IODP Legs. Celestine equilibrium can be reached through two different non-exclusive causes: a strontium increase in porewater linked to the dissolution of Sr-rich aragonite or biogenic calcite and precipitation of Sr-poor calcite (carbonate recrystallization), or an increase in the strontium and sulfate porewater concentrations linked to a salinity increase due to the presence of brines.Sediments at most of the sites exhibiting celestine equilibrium share common characteristics such as a carbonate-rich lithology (typically higher than 80 wt.%) and a low organic carbon content (generally below 1 wt.%). These results indicate that modification of porewaters during burial diagenesis can easily lead to celestine saturation, especially in carbonate-rich sediments. We then briefly discuss former interpretations of the presence of celestine in ancient and recent marine sediments, as well as the consequences of the incorporation of celestine formation in diagenetic models using the porewater Sr content and Sr isotopic composition.  相似文献   

Denudation of the Côte d'Ivoire-Ghana transform continental margin from apatite fission tracks     

Florence Bigot-Cormier  Christophe Basile  Gérard Poupeau  Jean-Pierre Bouillin  Erika Labrin 《地学学报》2005,17(2):189-195

Apatite fission track analysis of samples from the shoulder (marginal ridge) of the Côte d'Ivoire-Ghana transform continental margin reveal a cooling of the margin between 85 and 65 Ma for the central and eastern parts of the ridge. All samples were heated in situ during sedimentary burial with a temperature >120 °C, except for two samples located in the eastern part which were heated between 105 and 120 °C. For the first time, age/depth diagram along a transform margin shows a shape involving erosion starting at the bottom of the continental slope, then stepping backwards towards the edge of the slope. This retrogressive erosion can result from the deepening of the lithospheric plate sliding along the transform margin, from thick continental crust to thin continental crust, and finally to oceanic crust. This process could be at the origin of the shoulder uplift by flexural response to the important crustal discharge (>2 km).  相似文献   

The N ii spectrum of the Orion nebula     

Vladimir Escalante  Christophe Morisset 《Monthly notices of the Royal Astronomical Society》2005,361(3):813-823

The predicted emission spectrum of N  ii is compared with observations of permitted lines in the Orion nebula. Conventional nebular models show that the intensities of the more intense lines can be explained by fluorescence of starlight absorption with a N abundance that is consistent with forbidden lines. Lines excited mostly by recombination, on the other hand, predict high N abundances. The effects of stellar and nebular parameters and of the atomic data on the predicted intensities are examined.  相似文献   

Hydrological processes of a rainforest headwater swamp from natural chemical tracing in Nsimi watershed,Cameroon     

Jean‐Christophe Maréchal  Jean‐Jacques Braun  Jean Riotte  Jean‐Pierre Bedimo Bedimo  Jean‐Loup Boeglin 《水文研究》2011,25(14):2246-2260

The hydrological role of a headwater swamp in a tropical rainforest is studied using chloride mass balance (CMB) and end‐member mixing analysis. There are three main contributions to streamflow: (1) the hillside bedrock aquifer, (2) overland flow from the swamp during storm events and (3) groundwater flow from the swamp aquifer. Before rainfall events of the wet season, the pre‐event water comprises a mix of 80% of bedrock aquifer and 20% of swamp aquifer. During storms, the relative contribution of overland flow increases according to the rainfall intensity and the initial saturation rate of the pre‐event water reservoirs. The yearly contribution of overland flow from the swamp to the stream is about 31%. The relationship between the swamp and the stream fluctuates with space and time. Generally, the swamp is drained by the stream; however, at the end of long dry seasons, after the first rains, indirect recharge occurs from the stream to the swamp with a hydraulic gradient inversion in the swamp aquifer. The net contribution of the swamp aquifer to the stream is only 4%, which is much lower than the hillside aquifer contribution of about 65%. Recharge on the swamp being very low, these results suggest that, except for a few storms at the end of the dry season, the Nsimi swamp does not contribute to flood attenuation. Evapotranspiration is higher on the hillside than in the swamp. Nevertheless, depletion of water stored within the swamp is dominated by evaporation rather than by its contribution to streamflow. The export of solutes through swamp groundwater flow below the weir is low (<7%). Nevertheless, the swamp is the most active area of weathering in the watershed. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Hydrological flowpaths and nitrate removal rates within a riparian floodplain along a fourth‐order stream in Brittany (France)     

Jean‐Christophe Clment  Luc Aquilina  Olivier Bour  Kristelle Plaine  Tim P. Burt  Gilles Pinay 《水文研究》2003,17(6):1177-1195

Three main reservoirs were identified that contribute to the shallow subsurface flow regime of a valley drained by a fourth‐order stream in Brittany (western France). (i) An upland flow that supplied a wetland area, mainly during the high‐water period. It has high N‐NO₃^? and average Cl^? concentrations. (ii) A deep confined aquifer characterized by low nitrate and low chloride concentrations that supplied the floodplain via flow upwelling. (iii) An unconfined aquifer under the riparian zone with high Cl^? and low N‐NO₃^? concentrations where biological processes removed groundwater nitrate. This aquifer collected the upland flow and supplied a relict channel that controlled drainage from the whole riparian zone. Patterns of N‐NO₃^? and Cl^? concentrations along riparian transects, together with calculated high nitrate removal, indicate that removal occurred mainly at the hillslope–riparian zone interface (i.e. first few metres of wetland), whereas dilution occurred in lower parts of the transects, especially during low‐water periods and at the beginning of recharge periods. Stream flow was modelled as a mixture of water from the three reservoirs. An estimation of these contributions revealed that the deep aquifer contribution to stream flow averaged 37% throughout the study period, while the contribution of the unconfined reservoir below the riparian zone and hillslope flow was more variable (from ca 6 to 85%) relative to rainfall events and the level of the riparian water table. At the entire riparian zone scale, NO₃^? removal (probably from denitrification) appeared most effective in winter, despite higher estimated upland NO₃^? fluxes entering the riparian zone during this period. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Parameterisation of incoming longwave radiation over glacier surfaces in the semiarid Andes of Chile     

Shelley MacDonell  Lindsey Nicholson  Christophe Kinnard 《Theoretical and Applied Climatology》2013,111(3-4):513-528

A good understanding of radiation fluxes is important for calculating energy, and hence, mass exchange at glacier surfaces. This study evaluates incoming longwave radiation measured at two nearby glacier stations in the high Andes of the Norte Chico region of Chile. These data are the first published records of atmospheric longwave radiation measurements in this region. Nine previously published optimised parameterisations for clear sky emissivity all produced results with a root mean square error (RMSE) ~20 W?m^?2 and bias within ±5 W m^?2, which is inline with findings from other regions. Six optimised parameterisations for incoming longwave in all sky conditions were trialled for application to this site, five of which performed comparably well with RMSE on daytime data <18 W?m^?2 and bias within ±6 W?m^?2 when applied to the optimisation site and RMSE <20 W?m^?2 and bias within ±10 W m^?2 when applied to the validation site. The parameterisation proposed by Mölg et al. (J Glaciol 55:292-302, 2009) was selected for use in this region. Incorporating the proposed elevation modification into the equation reduced the bias in the modelled incoming longwave radiation for the validation site. It was found that applying the parameterisation optimised in the original work at Kilimanjaro produced good results at both the primary and validation site in this study, suggesting that this formulation may be robust for different high mountain regions.  相似文献   

Marginal abatement cost curves and the quality of emission reductions: a case study on Brazil     

Adrien Vogt-Schilb  Stéphane Hallegatte  Christophe de Gouvello 《Climate Policy》2013,13(6):703-723

Decision makers facing emission-reduction targets need to decide which abatement measures to implement, and in which order. This article investigates how marginal abatement cost (MAC) curves can inform such a decision. We re-analyse a MAC curve built for Brazil by 2030, and show that misinterpreting MAC curves as abatement supply curves can lead to suboptimal strategies. It would lead to (1) under-investment in expensive, long-to-implement and large-potential options, such as clean transportation infrastructure, and (2) over-investment in cheap but limited-potential options such as energy-efficiency improvement in refineries. To mitigate this issue, the article proposes a new graphical representation of MAC curves that explicitly renders the time required to implement each measure.

Policy relevance

In addition to the cost and potential of available options, designing optimal short-term policies requires information on long-term targets (e.g. halving emissions by 2050) and on the speed at which measures can deliver emission reductions. Mitigation policies are thus best investigated in a dynamic framework, building on sector-scale pathways to long-term targets. Climate policies should seek both quantity and quality of abatement, by combining two approaches: a ‘synergy approach’ that focuses on the cheapest mitigation options and maximizes co-benefits, and an ‘urgency approach’ that starts from a long-term objective and works backward to identify actions that need to be implemented early. Accordingly, sector-specific policies may be used (1) to remove implementation barriers on negative- and low-cost options and (2) to ensure short-term targets are met with abatement of sufficient quality. Indeed, such policies can avoid under-investment in the long-to-implement options required to reach long-term targets, which are otherwise difficult to enforce.  相似文献   

The phase 0/A study of the ESA M3 mission candidate EChO     

Ludovic Puig  Kate Isaak  Martin Linder  Isabel Escudero  Pierre-Elie Crouzet  Roger Walker  Matthias Ehle  Jutta Hübner  Rainer Timm  Bram de Vogeleer  Pierre Drossart  Paul Hartogh  Christophe Lovis  Giusi Micela  Marc Ollivier  Ignasi Ribas  Ignas Snellen  Bruce Swinyard  Giovanna Tinetti  Paul Eccleston 《Experimental Astronomy》2015,40(2-3):393-425

  相似文献