In:
Limnology and Oceanography, Wiley, Vol. 55, No. 3 ( 2010-05), p. 1338-1352
Kurzfassung:
The anaerobic mineralization of buried organic matter through sulfate reduction and methanogenesis was studied in 2‐m‐long piston cores of organic‐rich, silty‐clay sediment from two sites in Limfjorden, Denmark. An extended sulfate‐methane transition (SMT) zone was found at 1–1.5‐m sediment depth, accompanied by peaks in sulfide (4–6 mmol L −1 ) and high dissolved inorganic carbon (30–50 mmol L −1 ). Pore‐water acetate concentrations were 2‐10 µmol L ‐1 . 14 C‐acetate was oxidized to 14 CO 2 in the sulfate zone and reduced to 14 CH 4 at and below the SMT. CO 2 reduction was the predominant pathway of methanogenesis below the sulfate zone. Sulfate reduction rates (SRRs) determined by 35 S tracer experiments decreased with depth throughout the sulfate zone from 〉 100 nmol cm −3 d −1 near the sediment surface to 〈 1 nmol cm −3 d −1 at depth. The depth trend of rates was equally well described by a power law function and a reactive continuum model. Only a small percentage of the total 35 S‐SRR was due to anaerobic oxidation of methane. In contrast, diffusion‐reaction modeling of pore‐water sulfate indicated that sulfate reduction was insignificant throughout the sulfate zone and that most of the activity occurred at the SMT. A comparison of the burial flux of organic carbon below the sulfate zone and the returning flux of methane indicated that the diffusion modeling of pore‐water sulfate strongly underestimated in situ SRRs, whereas the 35 S data may have overestimated the rates at depth. Modeled and measured SRR could be reconciled provided that bioirrigation reached to at least 20–40‐cm sediment depth, which appears realistic given the predominant burrowing polychaete fauna.
Materialart:
Online-Ressource
ISSN:
0024-3590
,
1939-5590
DOI:
10.4319/lo.2010.55.3.1338
Sprache:
Englisch
Verlag:
Wiley
Publikationsdatum:
2010
ZDB Id:
2033191-5
ZDB Id:
412737-7
SSG:
12
SSG:
14
