Direct O 2 control on the partitioning between denitrification and dissimilatory nitrate reduction to ammonium in lake sediments

Cojean, Adeline N. Y.; Zopfi, Jakob; Gerster, Alan; Frey, Claudia; Lepori, Fabio; Lehmann, Moritz F.

Lacustrine sediments are important sites of fixed-nitrogen (N) elimination through the reduction of nitrate to inline-formulaN2 by denitrifying bacteria, and they are thus critical for the mitigation of anthropogenic loading of fixed N in lakes. In contrast, dissimilatory nitrate reduction to ammonium (DNRA) retains bioavailable N within the system, promoting internal eutrophication. Both processes are thought to occur under oxygen-depleted conditions, but the exact inline-formulaO2 concentration thresholds particularly of DNRA inhibition are uncertain. In inline-formulaO2 manipulation laboratory experiments with dilute sediment slurries and inline-formula M7inlinescrollmathml chem normal 15 normal NO normal 3 - 35pt17ptsvg-formulamathimg16ab11aa7134fedd76e0397b069cb409 bg-16-4705-2019-ie00002.svg35pt17ptbg-16-4705-2019-ie00002.png additions at low- to sub-micromolar inline-formulaO2 levels, we investigated how, and to what extent, oxygen controls the balance between DNRA and denitrification in lake sediments. In all inline-formulaO2-amended treatments, oxygen significantly inhibited both denitrification and DNRA compared to anoxic controls, but even at relatively high inline-formulaO2 concentrations (inline-formula≥70inline-formulaµmol Linline-formula−1), nitrate reduction by both denitrification and DNRA was observed, suggesting a relatively high inline-formulaO2 tolerance. Nevertheless, differential inline-formulaO2 control and inhibition effects were observed for denitrification versus DNRA in the sediment slurries. Below 1 inline-formulaµmol Linline-formula−1inline-formulaO2, denitrification was favoured over DNRA, while DNRA was systematically more important than denitrification at higher inline-formulaO2 levels. Our results thus demonstrate that inline-formulaO2 is an important regulator of the partitioning between N loss and N recycling in sediments. In natural environments, where inline-formulaO2 concentrations change in near-bottom waters on an annual scale (e.g., overturning lakes with seasonal anoxia), a marked seasonality with regards to internal N eutrophication versus efficient benthic fixed-N elimination can be expected.



Cojean, Adeline N. Y. / Zopfi, Jakob / Gerster, Alan / et al: Direct O2 control on the partitioning between denitrification and dissimilatory nitrate reduction to ammonium in lake sediments. 2019. Copernicus Publications.


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