Chemodenitrification is the abiotic reaction of nitrite and ferrous iron that leads to nitrous oxide production. Cable bacteria can increase the availability of both reactants in sediment porewater by mediating nitrate reduction to nitrite and by promoting the dissolution of FeS minerals. We thereby hypothesized that chemodenitrification is stimulated in sediment with cable bacteria. Sediment cores from Aarhus harbour (Denmark) were incubated under aerated, nitrate-amended water. Additional sediment cores were provided with filters at 0.3 cm depth to minimize cable bacteria growth. Electric fields diagnostic of cable bacteria activity developed to intensities up to three fold higher in the treatment cores compared to the filter controls over a two-week period. Nitrous oxide was sporadically detected in the filter-controls (max conc. 5 µM), whereas it was consistently present in the treatment cores reaching concentrations up to 20 µM in the sediment subsurface. Nitrous oxide production occurred below the oxygen penetration depth excluding possible contribution from nitrification. Notably, nitrous oxide production rates and electric field intensities were positively correlated both in treatment (Pearson, r=0.96, p=0.001) and filter-control cores (Pearson, r=0.80, p=0.057). These results clearly link cable bacteria activity to nitrous oxide production. Abiotic tests are needed to quantify the chemical vs. biological contribution to the production of nitrous oxide.

Primary Presenter: Ugo Marzocchi, Aarhus University (ugomar@bio.au.dk)

Authors:

Mie Mai Corneliussen, Aarhus University, Center for Electromicrobiology  ()

Julia Otte, Aarhus University, Center for Electromicrobiology  ()

Andreas Schramm, Aarhus University, Center for Electromicrobiology  ()