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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: 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: 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: SUMMARY Lake Pavin, French Massif Central, is the main meromictic Iake in France and has been extensively studied from more than 50 years. The upper part (mixolimnion) at a depth of less than about 60 m behaves as an oligotrophic lake and is oxic during the major part of the year. The lower layer (monimo- limnion) has a higher salinity and is permanently anoxie. Unlike the top of the mixolimnion, élément concentrations in the monimolimnion can be consi- dered at steady state. The boundary between mixolimnion and monimolim nion is a redox interface. At this interface, an important number of both chemical and biochemical reactions occur. This boundary, where élément concentrations vary greatly, was studied at the centimeter scale between 58 and 64 m depth. The présent paper is focu- sed on five éléments showing very différent behaviours: rubidium, iron, man ganèse, vanadium and barium. Sodium was used as a référence élément. Sodium and rubidium concentrations had similar patterns: a progressive increase began at 61 m depth and the maximal gradient was located at 63 m. They continue to increase towards the bottom of the lake. Iron concentra tions were low (< 1 |imol/L) at a depth less than 62.8 m and increased very sharply below this depth. Manganèse concentrations were very low in the mixolimnion (< 0.01 nmol/L), exhibited a peak between 62.4 and 63.5 m depth (up to 60 (imol/L at 63 m) and reached a value of about 30 |imol/L at 85 m. Barium concentrations began to increase only at depths greater than 65-67 m. Vanadium concentrations in the mixolimnion were about 14 nmol/L, decreased to a minimum below the détection limit at 62.2 m and then increase drastically (150 nmol/L at 85 m). In order to dérive the accurate location of the chemical reactions and an esti mation of their rates from the concentration profiles, knowledge of the trans-
