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ABSTRACT: A reactive transport model was developed to describe seasonal variations of biogeochemical and physical processes in Lake
Aydat. The model includes physical processes such as vertical mixing, sedimentation and advection related to inflows into
the lake and biogeochemical conversion processes in the water column and in the sediment surface layer. The reactions described
in the model include primary redox reactions such as primary production, aerobic and anaerobic respiration, methanogenesis
and secondary reactions established between oxidants and reducers produced by the primary reactions. After adjusting various
kinetic constants, the model reasonably reproduced the main features of seasonal variations of dissolved oxygen and nitrate
depth profiles and pH. The reactive transport model was also used to quantify the relative importance of different biogeochemical
pathways. For instance, ferrous denitrification seems to play an important role when stratification is increasing.
KeywordsEutrophic lake-Reactive-transport model-Biogeochemistry-Redox
Aquatic Geochemistry 04/2012; 16(4):587-610. · 1.90 Impact Factor
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Applied Geochemistry 01/2008; 23(10):2800-2816. · 2.18 Impact Factor
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ABSTRACT: Thin-films techniques introduced by W. Davison et al. in early 1990’s are well adapted to study distribution of dissolved compounds in sediment of aquatic systems. We present here a development for inorganic phosphate distribution (
ASLO Aquatic Sciences Meeting 2009;
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ABSTRACT: Sepetiba bay is a shallow semi enclosed water body located about 70km on the west side of the city of Rio de Janeiro with an area of 450km² separated from the Atlantic Ocean by a sand spit. Fishing, shrimp and tourism are important economic activities. During 35 years a Zinc/Cadmium smelter has polluted the bay. The objective of this investigation is to demonstrate how diagenetic processes are responsible for the cadmium remobilization out or fixation into the sediment column.. Two contrasting sites were selected to compare the diagenetic process. P1 located near to the smelter and P2 is about 20km away from the smelter next to a domestic effluents discharge into the bay. Peeper samplers with 25 cells with a resolution of 2,5cm were introduced into the sediment at both sites. After a period of 3 weeks equilibrium, the pore waters were separated from each cell and analyzed within 24 hours for alkalinity, H2S, NH3 and soluble phosphate by conventional methods An ICP-AES spectrometer was used to analyze Na, Mg, Li, Ba, Sr, Si, Fe and Mn. The total and labile Cd in pore waters were determined by differential-pulse stripping voltammetry. The solute profiles have revealed that the sediments at both sites were anoxic. The slopes of the ferrous and sulfide profile constituents permitted characterization the area at P1 as ferrous dominant with oxic conditions in the overlying water and P2 as a sulfidic rich environment with suboxic conditions in the water column. At P1 total dissolved Cd in the overlying water was about 450pM and labile fraction varied from 85 to 177pM. Just below the sediment water interface 695pM of total dissolved Cd was observed. Probably diagenetic processes are responsible for release of cadmium at the sediment interface. Below this maxima Cd concentrations decreased to 30pM. At P2 a concentration o of 150pM of total dissolved Cd was detected in the overlying water and samples in the pore waters at the sediment interface had an average concentration of 20pM. The downward diffusion of dissolved Cd in the pore water probably facilitated the formation of Cd sulfide or adsorption on particulate matter.
American Geophysical Union, Fall Meeting 2006;
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The 7th International Symposium on Environmentla Geochemistry;
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ABSTRACT: Solid sediment, pore and epibenthic waters were collected from the Thau lagoon (France) in order to study the post-depositional partition and mobility of mercury in organic rich sediment. Total Hg (HgT) and monomethylmercury (MMHg) profiles were produced in both dissolved and solid phases. The distribution of HgT in the solid phase appeared to be related to the historical changes in the Hg inputs into the lagoon. HgT was in equilibrium between solid and solution phases in the sulfidic part of the cores, with a mean log Kd of 4.9 ± 0.2. The solid phase appeared to be a source of HgT for pore water in the upper oxic to suboxic parts of the cores. The MMHg represented a small fraction of HgT: 3–15% and 0.02–0.80% in the dissolved and solid phases, respectively. Its distribution was characterized by a main peak in the superficial sediments, and another deeper in the core within the sulfide-accumulating zone. In addition, high dissolved MMHg concentrations and methylated percentage were found in the epibenthic water. Ascorbate (pH 8) dissolution of the sediments and analyses of the soluble fraction suggest that the amorphous oxyhydroxides played a major role in controlling total and methylmercury mobility throughout the sediment–water interface. These features are discussed in terms of sources, transfer and transformations. Diffusive fluxes of HgT and MMHg from sediment to the water column for the warm period were estimated to be 40 ± 15 and 4 ± 2 pmol m−2 d−1, respectively.
Estuarine, Coastal and Shelf Science.
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ASLO Summer Meeting;
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European Geophysical Society, XXIII assembly;
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ABSTRACT: Methane is a powerful greenhouse gas and its concentration in the atmosphere has increased over the past decades. Methane produced by methanogenic Archae can be consumed through aerobic and anaerobic oxidation pathways. In anoxic conditions found in freshwater environments such as meromictic lakes, CH4 oxidation pathways involving different terminal electron acceptors such as , , and oxides of Fe and Mn are thermodynamically possible. In this study, a reactive transport model was developed to assess the relative significance of the different pathways of CH4 consumption in the water column of Lake Pavin. In most cases, the model reproduced experimental data collected from the field from June 2006 to June 2007. Although the model and the field measurements suggest that anaerobic CH4 oxidation may contribute to CH4 consumption in the water column of Lake Pavin, aerobic oxidation remains the major sink of CH4 in this lake.Highlights► Aerobic and anaerobic methane oxidations likely occur in the water column of Lake Pavin. ► Seasonal differences in aerobic and anaerobic methane oxidation rates are detected. ► Iron dependent anaerobic methane oxidation may contribute to methane consumption in the water column. ► Aerobic methane oxidation appears as the major sink of methane in the Lake Pavin.
Applied Geochemistry 26(12):1919-1932. · 2.18 Impact Factor
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ABSTRACT: Vertical distributions of dissolved species across the sediment–water interface (SWI), including major cations (sodium, potassium, magnesium, calcium), minor cations (lithium, strontium, barium), redox sensitive species (dissolved manganese, iron, sulfate, sulfide, ammonium) and other chemical parameters (pH, alkalinity, soluble reactive phosphorous, dissolved silica) were studied in a Mediterranean lagoon used for intensive shellfish farming. In order to quantify the impact of this activity on diagenetic processes and the influence of seasonal changes, two stations contrasted with respect to organic carbon fluxes were sampled in Thau lagoon from March 2001 to August 2002 during four field campaigns in winter, spring, summer and fall. Well-defined layers enriched with redox sensitive species were observed following the conventional sequence of early diagenetic reactions. However, differences were observed between both stations in depths and thickness layers. Concentration gradients extended down to more than 92 cm depth at the central position of the lagoon (station C4 – 8 m depth) and down to 40 cm depth inside shellfish farming zones (station C5 – 9 m depth). Station C4 showed an unusual diagenetic signature: sharp dissolved oxygen, iron, nitrate and manganese gradients existed at the SWI but gradients of dissolved sulfide and alkalinity as well as other parameters (dissolved silica, Ba, etc.) were recorded only from 25 to 30 cm depth downward. Seasonal changes were observed in pore water composition as deep as 30–50 cm in station C4 (only 15 cm in station C5). The center of the lagoon is not directly subjected to biodeposits deriving from shellfish activity. Isotopic and bioturbation data allowed to rule out a reworking of the sediment deeper than a few centimeters. In addition to organic content of the sediment, physical parameters were likely to induce the 10–20 cm gap between dissolved iron and sulfide profile as well as the higher vertical extent of diagenetic sequence observed at station C4. Conversely to station C5, station C4 underwent stronger currents and wave effect probably generating advective transport of water through the sediment, but no permeability data were available to confirm this hypothesis. During summer, climatic conditions generated vertical stratification of the water column and transient suboxic conditions at the bottom. Such conditions drove the upward shift of redox fronts, compacting the diagenetic sequence. These effects were reinforced at station C5 by shellfish and its farm structures (mainly attenuation of current and increased heat absorption).
Estuarine, Coastal and Shelf Science.
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ABSTRACT: Lac Pavin (French Massif Central) is a permanently stratified lake: the upper water layers (mixolimnion, from 0 to 60 m depth) are affected by seasonal overturns, whereas the bottom water layers (monimolimnion, from 60 to 90 m depth) remain isolated and are never mixed. Hence, they are capable of storing important quantities of dissolved gases, mainly CO2. With the aim of better constraining the water balance and of gaining new insights into the carbon cycle of Lac Pavin, an isotopic approach is used. The δ18OH2O profiles lead the authors to give a new evaluation of the evaporation flow rate (8 L s−1), and to propose and characterize two sub-surface springs. The sub-surface spring located at the bottom of the lake can be deduced from the 1% isotopic difference between the upper water layers (mean δ18OH2O value: −7.3‰) and the bottom water layers (δ18OH2O=-8.4‰). It is argued that this sub-surface spring has isotopic and chemical characteristics similar to those of the magmatic CO2-rich spring (i.e. Fontaine Goyon, δ18OH2O=-9.4‰), and we calculate its flow rate of 1.6 L s−1. The second sub-surface spring is located around 45 m depth, with a composition close to those of the water surface streams (δ18OH2O<-7.6‰).Methane (4 mM) and dissolved inorganic carbon concentrations (≈14 mM) allow the re-estimation of the relative DIC contributions in the bottom of the lake (90 m depth): 1/3 deriving from methanogenesis (δ13CDIC ≈ +7‰) and 2/3 from the magmatic CO2-rich spring (δ13CDIC ≈ −5‰). Above 80 m depth, the variations in DIC concentrations (ranging from 0.5 to 10 mM) and δ13CDIC values (ranging from −6.5‰ to 4.4‰) are partly explained by the usual methanotrophy, organic matter oxidation, photosynthesis and CO2 equilibrium with atmosphere. The unusually high δ13CDIC values in the upper water layers (ranging from −6‰ to 0‰) compared to the expected δ13CDIC values assuming only organic matter oxidation, demonstrate the leakage of 13C-enriched DIC from the bottom water layers of Lac Pavin (δ13CDIC values ranging from −5‰ to 3‰).
Applied Geochemistry 23(10):2800-2816. · 2.18 Impact Factor
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ABSTRACT: DGT (Diffusive Gradient in Thin-films) and DET (Diffusive Equilibration in Thin-films) combined probes were used in Thau lagoon sediments to describe variations of dissolved concentrations of metals such as cadmium, manganese and iron, through the sediment–water interface. Two contrasted stations regarding organic carbon fluxes were studied from December 2001 to May 2003 during four field campaigns: station C4 in the middle of the lagoon, and station C5 in a shellfish-farming zone. Laboratory experiments and field deployments in such environment showed that DGT sampled pore water labile cadmium whereas iron and manganese concentrations were underestimated. These results suggest that no steady state in the flux of metals onto the gel was established for Fe and Mn. Kinetics of metal sulfide dissolution–precipitation may control metal fluxes onto the gel probe in marine sedimentary environments. Analysis of sediment and water column samples showed cadmium concentrations above natural background (3.3 and 7.6 nmol kg−1 for station C4 and station C5 sediments, respectively; between 40 and 800 pmol L−1 for the water column), suggesting contamination. Spatial and temporal patterns of cadmium behavior were observed. The sediment at station C4 was generally a source of cadmium whereas at station C5 it was a sink. The vertical extension of the diagenetic series was more important at station C4 with deeper oxygen penetration and lack of dissolved sulfide whereas station C5 showed steep ∑H2S gradients at the same depths. The data suggested that cadmium source was more likely organic matter. Cadmium mobility was probably controlled by aerobic mineralization at station C4 and by dissolution–precipitation of sulfides at station C5. Seasonal variations were observed in the depth of oxygen penetration and sulfide diffusion generating important remobilization of cadmium during December 2001. Conversely in May 2003 at station C5, bottom water suboxic conditions (i.e. %O2 = 60) enhanced reductive conditions in the sediment favoring uptake of cadmium by the sediment from the water column.
Estuarine, Coastal and Shelf Science.
