Abstract
Fe(III) transformation to Fe(II) via the nitrate-dependent iron oxidation process, occurring in anoxic sediments, has an important role in the nitrogen cycle. In this study, laboratory experiments were performed to investigate the denitrification properties driven by nitrate-dependent iron oxidation. A 30-day incubation study of sediments and overlying water from Lake Moshui in Wuhan, China, was conducted in an anoxic condition. The nitrate reduction during the incubation was evaluated by the N2O emission and various forms of nitrogen in the overlying water. The denitrification enzyme activity and abundance of nitrate-dependent Fe(II)-oxidising bacteria were determined periodically, and their correlations with nitrogen and iron were analysed to illustrate the denitrification characteristics linked to Fe(II) oxidation in sediments. After the Fe(II) and nitrate input, the decrease of Fe(II) and nitrate concentrations was accompanied by an increase in nitrite and N2O production. The contribution of Fe(II) oxidation to the nitrate reduction accounted for 27.7% at the end of the incubation, and the rate of Fe(II) decrease was significantly correlated (P < 0.05) with the production of N2O. In addition, a positive correlation between denitrification enzyme activity and nitrate concentrations was observed. During incubation, the abundance of nitrate-dependent Fe(II)-oxidising bacteria in the sediment ranged from 1.1 × 105 cell g−1 wet sediment to 1.4 × 106 cell g−1 wet sediment, and increased with the increase of Fe(II) input concentration. The nitrate reduction coupled with Fe(II) oxidation was mainly mediated by microbial processes. Sediment denitrification was enhanced with increasing Fe(II) concentrations, and Fe(II) may play an important role in regulating nitrogen transformation in freshwater lakes.
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