Quantifying the contribution of reactive nitrogen loss through anaerobic ammonium oxidation in global wetlands and oxygen minimum zones

Anaerobic ammonium oxidation (anammox) plays a vital role in the global nitrogen cycle by mitigating reactive nitrogen. In recent years, its ecological importance has drawn increasing attention. Despite its widespread occurrence, the distribution and quantitative contribution of anammox to global nitrogen loss remain unclear. We collected 390 reported anammox activity measurements which were obtained using ¹⁵N isotope tracing techniques and analyzed anammox rate and environmental factors including soil/sediment and water property using generalized additive models (GAMs). Moreover, based on the division of the anammox activity region, we estimated anammox-driven nitrogen loss across different ecosystems including wetlands and oxygen minimum zones (OMZs) ecosystems. Our findings revealed that soil moisture content was the most significant predictor of anammox activity in wetlands ecosystems. Paddy fields contributed 51 % of anammox-driven nitrogen loss (32.0 Tg N/yr), followed by rivers/lakes (29 %) and wetlands (20 %). Asia emerged as the dominant region for anammox-driven nitrogen loss (30.7 Tg N/yr), with paddy fields making a substantial contribution. North America was the second-largest contributor (25.4 Tg N/yr), with rivers/lakes being the main sources of nitrogen loss. In OMZs ecosystems, nitrate and dissolved oxygen were key factors influencing anammox rates. OMZs were hotspots for anammox, with peak activity at 300 m depth and nitrogen loss totaling 68.6 Tg N/yr, mostly between 100 and 500 m depths. This study underscores the critical role of anammox in global nitrogen cycling and offers a basis for environmental nitrogen management through predictive anammox modeling.