Intermittent rivers in peri‑urban areas act as significant but overlooked sources of N₂O emissions

Intermittent rivers and ephemeral streams (IRES), which represent more than half of the global river network, remain largely understudied as potential sources of atmospheric nitrous oxide (N₂O), particularly in the context of peri‑urban areas experiencing intensive anthropogenic pressures (e.g., hydrological alterations, elevated organic matter (OM) and nutrient inputs). To address this critical knowledge gap, we conducted a multi-month investigation across Beijing's peri‑urban IRES network in China. N₂O flux dynamics were quantified across five distinct hydrological phases, including dry riverbeds, exposed riverbeds, isolated pools, standing open waters, and flowing waters, and underlying mechanisms were elucidated via integrated analysis of physicochemical variables and microbial gene profiles. Dry riverbeds exhibited the highest N₂O emissions (215±1060 μmol·m^-2·d^-1), primarily driven by denitrification facilitated by substrate accumulation, a high abundance of nitrogen transformation genes, and favorable moisture conditions. Rainfall-induced rewetting further stimulated microbial activities and short-term N₂O emissions in dry riverbeds. Fragmented hydrological phases (dry riverbeds, exposed riverbeds, and isolated pools) exhibited significantly higher N₂O fluxes than connected phases (standing open waters and flowing waters). The temporal dynamics of N₂O fluxes revealed significant decreases during hydrological wetting transitions from fragmented to connected phases and dry to partially saturated phases. These reductions were primarily due to enhanced microbial OM decomposition and favored complete denitrification, driven by increased terrestrial OM inputs, reduced nirS and nirK gene abundances, and elevated ratios of dissolved organic carbon to nitrate. Peri-urban IRES emitted significantly more N₂O during hydrological phase transitions than perennial rivers did during the study period. Our findings demonstrate that IRES can be significant N₂O sources, particularly in peri‑urban areas due to high emissions during dry phases. This study advances the understanding of N₂O emission patterns and mechanisms in IRES, emphasizing their previously overlooked role in global N₂O budgets, with implications for N₂O emission mitigation through environmental flow management.