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Abstract

Denitrification has long been regarded as the only pathway for terrestrial nitrogen (N) loss to the
atmosphere. Here we demonstrate that large-scale anaerobic ammonium oxidation (anammox),
an overlooked N loss process alternative to denitrification which bypasses nitrous oxide (N 2 O), is
ubiquitous in inland waters of China and contributes significantly to N loss. Anammox rates in aquatic
systems show different levels (1.0–975.9 μmol N m −2 h −1 , n = 256) with hotspots occurring at oxic-
anoxic interfaces and harboring distinct biogeochemical and biogeographical features. Extrapolation
of these results to the China-national level shows that anammox could contribute about 2.0 Tg
N yr −1 , which equals averagely 11.4% of the total N loss from China’s inland waters. Our results
indicate that a significant amount of the nitrogen lost from inland waters bypasses denitrification,
which is important for constructing more accurate climate models and may significantly reduce
potential N 2 O emission risk at a large scale.