Emission and oxidation of methane in a meromictic, eutrophic and temperate lake (Dendre, Belgium).
We sampled the water column of the Dendre stone pit lake (Belgium) in spring, summer, autumn and winter. Depth profiles of several physico-chemical variables, nutrients, dissolved gases (CO2, CH4, N2O), sulfate, sulfide, iron and manganese concentrations and δ13C-CH4 were determined. We performed incubation experiments to quantify CH4oxidation rates, with a focus on anaerobic CH4oxidation (AOM), without and with an inhibitor of sulfate reduction (molybdate). The evolution of nitrate and sulfate concentrations during the incubations was monitored. The water column was anoxic below 20 m throughout the year, and was thermally stratified in summer and autumn. High partial pressure of CO2and CH4and high concentrations of ammonium and phosphate were observed in anoxic waters. Important nitrous oxide and nitrate concentration maxima were also observed (up to 440 nmol L-1and 80 μmol L-1, respectively). Vertical profiles of δ13C-CH4unambiguously showed the occurrence of AOM. Important AOM rates (up to 14 μmol L-1d-1) were observed and often co-occurred with nitrate consumption peaks, suggesting the occurrence of AOM coupled with nitrate reduction. AOM coupled with sulfate reduction also occurred, since AOM rates tended to be lower when molybdate was added. CH4oxidation was mostly aerobic (∼80% of total oxidation) in spring and winter, and almost exclusively anaerobic in summer and autumn. Despite important CH4oxidation rates, the estimated CH4fluxes from the water surface to the atmosphere were high (mean of 732 μmol m-2d-1in spring, summer and autumn, and up to 12,482 μmol m-2d-1in winter).
Chemical Oceanography Unit, Université de Liège, Belgium. Electronic address: froland@doct.ulg.ac.be.
Fleur A E
FAE
Roland
Chemical Oceanography Unit, Université de Liège, Belgium.
François
F
Darchambeau
Department of Earth and Environmental Sciences, Katholieke Universiteit Leuven (KU Leuven), Belgium.
Cédric
C
Morana
Department of Earth and Environmental Sciences, Katholieke Universiteit Leuven (KU Leuven), Belgium.
Steven
S
Bouillon
Chemical Oceanography Unit, Université de Liège, Belgium.
Alberto V
AV
Borges
D064751:Ammonium Compounds / Q000032:analysis; D000693:Anaerobiosis; D001272:Atmosphere; D001530:Belgium; D002245:Carbon Dioxide / Q000032:analysis; D007501:Iron / Q000032:analysis; D060106:Lakes / Q000737:chemistry*; D008345:Manganese / Q000032:analysis; D008697:Methane / Q000032:analysis / Q000737:chemistry*; D009566:Nitrates / Q000032:analysis / Q000737:chemistry*; D009609:Nitrous Oxide / Q000032:analysis; D010084:Oxidation-Reduction; D010710:Phosphates / Q000032:analysis; D012621:Seasons; D013431:Sulfates / Q000032:analysis / Q000737:chemistry*; D013440:Sulfides / Q000032:analysis
D064751:Ammonium Compounds; D009566:Nitrates; D010710:Phosphates; D013431:Sulfates; D013440:Sulfides; D002245:Carbon Dioxide; D008345:Manganese; D007501:Iron; D009609:Nitrous Oxide; D008697:Methane
Anaerobic methane oxidation; Carbon dioxide; Greenhouse gases; Lake; Methane emission; Nitrous oxide