Abiotic N2O Formation Across the Land–Ocean Continuum: An Overlooked Source of Nitrous Oxide via Abiotic Formation Across the Land–Ocean Continuum

Nitrous oxide (N₂O) production in the biosphere is traditionally attributed to microbial nitrification and denitrification. Recent studies suggest that N₂O can be produced via chemodenitrification, i.e., the reduction of nitrite to N₂O, which remains a major uncertainty in global N₂O budget. By conducting ¹⁵N-tracer incubations, samples from a land–ocean continuum demonstrated that the significance of N₂O production via chemodenitrification may be overlooked, particularly at metal-rich, acidic and anoxic conditions. Transition metals beyond iron, specifically manganese and zinc, drive abiotic N₂O formation in both oxic and anoxic environments. And the rates are significantly enhanced under lower oxygen concentration. In natural estuarine waters, abiotic N₂O production is modest but consistent (0.0001–0.0013 nmol N L^-1 d^-1). In contrast, acidic metal-rich mine wastewater stimulated abiotic N₂O production up to 138 nmol N L^-1 d^-1. Furthermore, at the interface where mine drainage contaminating soils, N₂O efflux reached 446 μmol N m^-2 d^-1, rivaling or exceeding emissions from many intensively managed croplands. In these hotspots, abiotic and biotic processes act in concert to sustain elevated N₂O production, with microbial activity potentially modulating substrate availability for abiotic production. These findings highlight the necessity to integrate chemodenitrification into regional and global nitrogen assessments to improve the accuracy of N₂O budget.