Interactive comment on “Occurrence of benthic microbial nitrogen fixation coupled to sulfate reduction in the seasonally hypoxic Eckernförde Bay, Baltic Sea” by V. J. Bertics et al

Interactive comment on “Occurrence of benthic microbial nitrogen fixation coupled to sulfate reduction in the seasonally hypoxic Eckernförde Bay, Baltic Sea” by V. J. Bertics et al

Interactive comment on “Occurrence of benthic microbial nitrogen fixation coupled to sulfate reduction in the seasonally hypoxic Eckernförde Bay, Baltic Sea” by V. J. Bertics et al

The Bertics et al. manuscript addresses the potential simultaneous occurrence of sulfate reduction and N fixation in anaerobic core horizons from the Baltic Sea. This work adds new data to the observations that sulfate-reducing bacteria fix nitrogen. Overall, the technical approach is sound, the conclusions regarding N fixation sound, and the paper is well written. I believe the work to be time...

Interactive comment on “Occurrence of benthic microbial nitrogen fixation coupled to sulfate reduction in the seasonally hypoxic Eckernförde Bay, Baltic Sea” by V. J. Bertics et al

We agree with the referee that this remains puzzling, however it is not our intention to determine why SRB fix nitrogen, but merely to provide more evidence that N2 fixation, possibly by SRB, exists in benthic systems. We have added in a citation (Knapp, 2012) that goes into great detail about the possible reasons for this occurrence and summarizes the many studies that have also documented ben...

Supplemental - Occurrence of benthic microbial nitrogen fixation coupled to sulfate reduction in the seasonally hypoxic Eckernförde Bay, Baltic Sea

1 Materials and Methods 1.1 Organic carbon slurries From two sediment cores (length ~ 60 cm, inner diameter 10 cm) collected from Eckernförde Bay on 13 April 2012, 500 ml of sediment from the top 0 5 cm was transferred into a 1 L glass 10
 bottle containing 500 ml of artificial seawater medium for SR bacteria from the Baltic Sea (salinity 23) (Widdel and Bak, 1992), creating a 1:1 medium:sedime...

Microbial methanogenesis in the sulfate-reducing zone of sediments in the Eckernförde Bay, SW Baltic Sea

Benthic microbial methanogenesis is a known source of methane in marine systems. In most sediments, the majority of methanogenesis is located below the sulfatereducing zone, as sulfate reducers outcompete methanogens for the major substrates hydrogen and acetate. The coexistence of methanogenesis and sulfate reduction has been shown before and is possible through the usage of noncompetitive sub...