Environmental Engineering Reference
In-Depth Information
methane, sulfate reduction, methanogenesis, anaerobic oxidation of methane
(AOM), cold methane seeps, mud volcanoes
1. INTRODUCTION
The presence of hydrogen sulfide dissolved in the water column of the deep
Black Sea was discovered more than hundred years ago during the expedition of
the Russian Geographic Society [4]. At that time a microbial origin of hydrogen
sulfide produced in the Black Sea was assumed [100]. In the following years,
two alternate hypotheses were made in order to explain the origin of H
2
S.
Biologists and chemists had an opinion that most of the Black Sea hydrogen
sulfide was produced by sulfate-reducing bacteria in the water column and
sediments. Some geologists offered the migratory hypothesis by which H
2
S
discharges into the sea from ancient rocks through tectonic fractures or from
mud volcanoes at the sea bottom [92].
Various arguments were made in order to prove the microbiological hypoth-
esis. Danilchenko and Chigirin [18] have observed decrease in the SO
4
2
−
/Cl
−
ratio with depth and argued that hydrogen sulfide is produced in the water col-
umn. These investigations were continued by Skopintsev [90] and Bezborodov
and Eremeev [6]. Issachenko [53] and Kriss [62] investigated the distribution
of sulfate-reducing and putrefactive bacteria in details. They suggested that
the bulk of the Black Sea hydrogen sulfide is produced in bottom sediments.
Sorokin [91] came to the same conclusion when he carried out first experiments
estimating the rates of sulfate reduction under in situ conditions with Na
35
SO
4
.
The investigations of the isotopic composition of hydrogen sulfide and sulfate
in the water column and pore waters were started by Vinogradov, Grinenko and
Ustinov [94] and continued by a number of Russian and foreign scientists. The
detailed analysis of the data obtained and their role in understanding of the
sulfur cycle of the Black Sea are main objectives of this review.
Microbial processes of the sulfur and carbon cycles are closely related. Most
of well known species of sulfate reducing bacteria are heterotrophs consuming
two moles of organic carbon to reduce one mole of sulfate. Many microor-
ganisms participating in the oxidative part of the sulfur cycle are chemo- and
photoautotrophs producing organic compounds at the expense of aerobic or
light-dependent anaerobic oxidation of H
2
S and other reduced compounds of
sulfur.
The second objective of our work is to discuss the processes of production
and consumption of organic carbon in the Black Sea with particular emphasis
on the
12
C/
13
C fractionation. Investigations of the stable isotopic composition
of particulate organic matter in the Black Sea began in 1969 during the “Atlantis
II” cruise [24, 25]. Most of recent studies have analyzed δ
13
C of suspended
organic matter in the water column and bottom sediments of the central Black
Sea. We have studied biogeochemical processes on the north-western shelf
