Abstract
Abstract. Lacustrine sediments are important sites of fixed-nitrogen (N) elimination through the reduction of nitrate to N2 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 O2 concentration thresholds
particularly of DNRA inhibition are uncertain. In O2 manipulation
laboratory experiments with dilute sediment slurries and
15NO3- additions at low- to sub-micromolar O2 levels, we
investigated how, and to what extent, oxygen controls the balance between
DNRA and denitrification in lake sediments. In all O2-amended
treatments, oxygen significantly inhibited both denitrification and DNRA
compared to anoxic controls, but even at relatively high O2
concentrations (≥70 µmol L−1), nitrate reduction by both
denitrification and DNRA was observed, suggesting a relatively high O2
tolerance. Nevertheless, differential O2 control and inhibition effects
were observed for denitrification versus DNRA in the sediment slurries.
Below 1 µmol L−1 O2, denitrification was favoured over DNRA,
while DNRA was systematically more important than denitrification at higher
O2 levels. Our results thus demonstrate that O2 is an important
regulator of the partitioning between N loss and N recycling in sediments.
In natural environments, where O2 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.
Funder
Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
Cited by
18 articles.
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