Processes and Driving Mechanisms of Nitrogen Removal in the Rivers on the Southeastern Qinghai‐Tibet Plateau

Abstract Denitrification and anaerobic ammonium oxidation (anammox) are key processes in mitigating nitrogen (N) pollution in river ecosystems. However, there has been insufficient investigation of the riverine N‐removal processes on the Qinghai‐Tibet Plateau (QTP). This study investigated the driving mechanisms of denitrification and anammox in 23 small rivers using multiple approaches (remote sensing, 15 N pairing, and molecular techniques). The rivers span large elevational and climatic gradients, offering an ideal window for studying the riverine N‐removal processes, especially in the context of global change. The denitrification rates were 1.37 ± 2.88 mg N/kg/d in summer and 0.21 ± 0.26 mg N/kg/d in winter, which dominated the total riverine N removal (96% and 73%, respectively). Structural equation models (SEM) revealed that geographic factors (elevation and land use), water properties (water temperature, pH, etc.), sediment parameters (moisture, NO 3 − ‐N, NH 4 + ‐N, etc.), and microbial gene abundances collectively explained over 60% of the variation in N‐removal rates, with sediment properties being the primary regulating factors in summer. In winter, SEM showed that the contribution of geographic factors increased. We proposed a framework combining cross‐perspective methods for revealing in‐river N removal mechanisms and predicted that, under global change, N removal processes in rivers on the QTP are likely to intensify in the future. The integrated approaches systematically offered critical insights into the processes and drivers of biogeochemical N cycling on the QTP.