Significant spatial heterogeneity and distinct determinants of N2O emission in Pearl River Estuary, China

Estuaries play a crucial role in the global nitrous oxide (N₂O) budget, but significant uncertainties remain in estimating their emissions due to anthropogenic impacts, particularly wastewater discharge. Using advanced high-resolution, real-time measurements, this study reveals that the Pearl River Estuary is a substantial N₂O emission source, estimated at 1.05 Gg yr^-1 (range: 0.92-1.23 Gg yr^-1) with pronounced spatial heterogeneity. Wastewater discharge significantly enhances emissions by introducing abundant nutrients, altering carbon-to-nitrogen stoichiometry, and stimulating biochemical processes. A meta-analysis further demonstrates that nitrogen inputs from wastewater widely increase N₂O emissions in global estuaries, though emission factors are considerably lower than IPCC estimates due to biological saturation. These findings highlight the need for refined emission factor estimates through comprehensive bottom-up studies to better understand estuarine contributions to the global N₂O budget.