Environmental Engineering Reference
In-Depth Information
on the inverse relationship between the rate of sulfate reduction and
32
S/
34
S fractionation.
3. Distinct seasonal changes of the isotopic composition of POC have been
observed. In early spring and summertime during phytoplankton blooms,
POC is less depleted in
13
C.
4. An additional depletion in
13
C of POC was observed in the zone of active
development of phototrophic and chemoautotrophic microorganisms at
the oxic/anoxic interface. The isotopically light biomass of autotrophic
microorganisms is rapidly consumed by anaerobic heterotrophic microor-
ganisms, mainly by sulfate-reducing bacteria.
5. Analysis of the geochemical activity of microorganisms participating in
the methane cycle as well as from the data on the isotopic composition
of the Black Sea methane show that about 80% of methane dissolved
in the water column is generated due to in situ activity of methanogens.
Methane fluxes from cold seeps and mud volcanoes are responsible for
an additional 10% of the methane production each. Methane coming
from bottom sediments does not play any significant role in the methane
balance of the water column.
6. A large-scale anaerobic methane oxidation was detected in the water
column, bottom sediments, and close to cold seep vents and mud volca-
noes. This process is followed by the accumulation of isotopically light
carbonate minerals and extremely light organic carbon of bacterial mats.
7. In anaerobic microniches of organic matter particles suspended in the aer-
obic water column, autotrophic methanogenesis takes place. This process
results in the formation of isotopically light methane, in aerobic waters.
A portion of this methane migrates from the water column to the at-
mosphere.
Acknowledgments
This work was supported by the Russian Academy of Sciences (grant MCB
RAS).
References
[1]
Albert D-B., Taylor C. and Martens C.S. Sulphate reduction rate and low molecular weight
fatty acid concentrations in the water column and surfical sediments of the Black Sea.
Deep Sea Res 1995; 42:1239-60.
[2]
Alekseev E.A. and Lebedev V.S. “Carbon isotope composition of CO
2
and CH
4
of the
Black Sea bottom sediments.“ In
Dissipated gases.
Moscow, VNIIYAGG, 1975. (In
Russian)
