Item

Abstract

Methanogenesis and iron reduction are microbial–mediated processes of biogeochem-
ical relevance. Due to thermodynamic reasons, they are deemed to occur in spatially
separated zones in marine subsurface sediments—a phenomenon referred to as bio-
geochemical zonation. Both processes have been observed to occur concomitantly in
incubations of marine subsurface sediment from the Helgoland mud area amended
with peptone.
In this thesis, I developed three incubations with marine subsurface sediment
from the Helgoland mud area from depths between 225–250 (HE406–4) and 250–275
(HE406–8) centimetres below the sea surface (cmbsf), and an analytical framework
to relate the measured concentrations of CO 2 , CH 4 and Fe(II) to the content of dry
sediment dynamically.
In incubations with sediment from a depth of 250–275 cmbsf, the use of a defi ned
amino acid mix (composed of alanine, glutamic acid, proline, leucine, and methionine)
at a concentration of ca. 10 mM induced the performance of CH 4 in levels comparable
to those found with peptone at a concentration of 1.7 g per litre. Iron reduction was
observed in association to methanogenesis in incubations amended with the amino
acid mix. However, the specifi c methanogenesis inhibitor 2–bromoethanesulphonate
(BES) was shown to impair iron reduction, for reasons beyond the scope of this thesis.
Furthermore, the study of the microbial community structure by T–RFLP in these
incubations revealed complex interaction patterns infl uenced by the addition of the
amino acid mix, ferrihydrite, and BES. Variation between incubation bottles and
diff erent incubation days were shown to be relevant as well.
In conclusion, the use of the amino acid mix and the analytical methods developed
provide a more quantitative approach for further incubation experiments.