Environmental Engineering Reference
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bottom. High methane oxidation rates were observed at and well below the
sulfide appearance where dissolved oxygen is absent. These data suggest that
methane in the Black Sea redox zone can be oxidized both aerobically and
anaerobically. Galchenko et al [8] isolated strains of methanotrophs being all
strict aerobes. They most probably dominate at the oxic/anoxic interface where
traces of oxygen may exist. Vetriani et al. [58] retrieved closely related to
Methylobacter psychrophilus
phylotype from the Black Sea chemocline and
amplified
pmoA
genes indicative of aerobic methane oxidation.
Below the H
2
S upper boundary the presence of active aerobic methanotrophs
is hardly possible. Molecular fingerprinting revealed that Archaea that belong
to ANME 2 cluster potentially responsible for anaerobic methane oxidation
are present in the Black Sea anoxic zone at the 305 m depth. Most recent
FISH data by Schubert et al. (this volume) confirmed the presence of ANME-1
and ANME-2 groups in the Black Sea water column. Consortia consisting of
sulfate-reducing bacteria and ANME 1 as well as ANME 2 groups were found
to be responsible for anaerobic methane oxidation in a number of sedimentary
environments [5, 35] and in microbial mats around Black Sea methane seeps
[24]. Vetriani et al. [58] have found several clones of δ-Proteobacteria related
to members of hydrocarbon-degrading consortia, the SAR406 cluster and to
Desulfobacterium anilini
in the anoxic water column including the oxic/anoxic
interface. The phylogenetic association of these δ-Proteobacteria was consid-
ered indicative for the presence of anaerobic methane oxidation in the Black
Sea water column. Yet 'typical' consortia of sulfate-reducers and methanogens
have not been found so far in the water column [for details on the anaero-
bic methane oxidation see Ivanov and Lein, this volume; Schubert et al., this
volume].
Methanobacteriales
and
Methanosarcinales
related archaea are most
probable groups involved in methanogenesis in the Black Sea water column
[58].
We have measured lithotrophic (using
14
CO
2
) and acetoclastic (using
14
C-
acetate), methanogenesis. Acetoclastic methanogenesis was usually responsible
for less than 5% of the total methanogenesis rate in the Black Sea water column
[Ivanov and Lein, this volume]. According to the classical model of redox zona-
tion, methanogenesis can occur only when sulfate reduction is ceased (e.g. [12]).
The Black Sea water column data however provide contradictory evidence.
Active sulfate reduction was observed together with high rates of litotrophic
methanogenesis up to 80 pmol l
−
1
d
−
1
measured using
14
C-bicarbonate at the
station in western halistase (Fig. 5B). Methane oxidation rates were at least one
order of magnitude higher than methanogenesis rate in the redox zone at this
station. Therefore we observed co-existence of sulfate reduction, supposedly
anaerobic methane oxidation and methanogenesis at the same depths in the
Black Sea anoxic zone. There are two possible explanations for this contro-
versy. (1) Methanogenic archaea can co-exist with sulfate-reducing bacteria if
