Figure 2

Conceptual model of the influences of nitrate or nitrite on microbial Fe-cycling and N₂O production based on the detected N₂O production rates [ppm g⁻¹ h⁻¹] or [nmol g⁻¹ h⁻¹]. The model is based on results of microcosm experiments with marine sediment from Norsminde Fjord amended with Fe(II) and nitrate, Fe(II) and nitrite (Fig. 1); or amended with nitrite only and native sediment (Fig. S1) (sterilized and microbially active setups). Thickness of lines and differences in symbol size indicate the relative importance. Heterotrophic denitrifiers are marked in light green, nitrate-reducing Fe(II)-oxidizers (NRFeOx) in dark green, and Fe(III)-reducers (FeRed) in red. Chemodenitrification reactions (abiotic reduction of nitrite by Fe(II), green rust or siderite) are highlighted in red. The orange mineral particle stands for iron minerals (e.g. FeOOH, green rust, siderite).