Bayraktarov, Elisa

Ferdelman, Timothy G.

Finster, Kai

Hubert, Casey

Price, Roy E.

University of Queensland eSpace

Geophysical Research Abstracts
Vol. 12, EGU2010-10100-15, 2010
EGU General Assembly 2010
© Author(s) 2010
Controls on Sulfate Reduction in Shallow Submarine Hydrothermal CO2 -
Venting Sediments (Milos Island, Greece)
Elisa Bayraktarov (1), Kai Finster (1,4), Roy E. Price (2), Casey Hubert (3), and Timothy G. Ferdelman (1)
(1) Max-Planck Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany (ebayrakt@mpi-bremen.de,
tferdelm@mpi-bremen.de /0049 421 2028 690 ), (4) Department of Biological Sciences, Section for Microbiology, Aarhus
University, Ny Munkegade 116, 8000 Aarhus, Denmark, (2) MARUM, Center for Marine Environmental Sciences, Leobener
Straße 28359 Bremen, Germany , (3) School of Civil Engineering and Geosciences, Newcastle Univerisity, Newcastle upon
Tyne, NE1 7RU United Kingdom
Microbial sulfate reduction is the dominant process in the anaerobic mineralization of organic matter in
continental margin sediments (Jørgensen, 1982). While sulfate-reducing bacteria (SRB) are generally accepted to
occur in environments of pH 6 – 8 (Widdel, 1988), recent studies have demonstrated sulfate reduction in low pH
habitats like acidic lakes and rivers, areas of acid mine drainage, and CO2-discharging hydrothermal vents. The
latter are of particular interest, representing a system in which the degassing-effects of previously sequestered CO2
can be investigated.
Incubation experiments were conducted on sediments from the low pH shallow-sea hydrothermal vent sys-
tem of Palaeochori Bay, Milos Island, Greece. Abundant gas venting of CO2 occurs throughout this bay, which
lowers the pH of pore fluids adjacent to gas venting to values of ca. 5 – 6. The objective for this research was
to investigate how changing pH and pCO2 affect sulfate reduction rates in a system in which the pH is naturally
reduced. The sediment in close proximity to the gas vent had an in-situ temperature of 75 ◦C (in 10 cm depth)
and was covered with whitish precipitates. This sediment was compared to 1) sediment from the transition zone
characterized by decreasing temperature, precipitates and increasing pH and 2) to ambient sediment showing no
irregularities in terms of temperature, pH and content of precipitates.
To test the effect of pH on bulk sulfate reduction in these sediments, incubations at pH values of 3, 4, 5, 6
and 7 were performed by adjusting the pH of SRB media with 1 M phosphoric acid or NaHCO3. In addition, the
effect of CO2-overpressure on the sulfate reduction rate was tested with respect to changing substrate. Different
substrates, including H2 and volatile fatty acids (VFA) mix which contained acetate, lactate, formate, succinate,
butyrate and propionate, were added to slurries of sediment and medium (1:1.5 v/v) and sulfate reduction rates
measured. Sediments not amended with external substrates showed increasing sulfate reduction rates with greater
distance from the vent site. The pH optimum for sulfate reduction during 16 hours incubation at 40 ◦C exhibited
different pH responses. Incubations of unamended transition zone sediment showed the highest rates of sulfate
reduction (14 nmol cm−3 day−1) being measured at pH 6, whereas incubation with the mixture of VFA electron
donors resulted in the highest measured sulfate reduction rate being 10 nmol cm−3 day−1 at pH 5. This may sug-
gest that VFA electron donors stimulate a more acid-tolerant SRB population. The effects of changing CO2 are
currently being evaluated.
B.B Jørgensen. Mineralization of organic matter in the sea bed–the role of sulfate reduction. Nature (London),
296, (1982) :643–645.
F. Widdel. Microbiology and ecology of sulfate- and sulfur-reducing bacteria. In: A.J.B. Zehnder, Editor, Biology
of Anaerobic Microorganisms, Wiley, New York, NY, (1988), pp. 469-585.


Controls on sulfate reduction in shallow submarine hydrothermal CO2-venting sediments (Milos Island, Greece)

http://espace.library.uq.edu.au/view/UQ:339759/UQ339759.pdf

Controls on sulfate reduction in shallow submarine hydrothermal CO2-venting sediments (Milos Island, Greece)

Abstract

Similar works

Full text

Available Versions

University of Queensland eSpace