Dredging changes the controls, pathways and environmental sensitivity of N₂O emissions in shallow lakes

Dredging is widely implemented to reduce internal nutrient loading in lakes, yet its effects on nitrous oxide (N₂O) emissions and environmental sensitivity remain poorly understood. This study conducted sediment-water column incubation experiments to investigate how dredging alters N₂O emissions in shallow lakes, focusing on biogeochemical properties, nitrogen-cycling functional genes, production pathways, and responses to warming and eutrophication. Dredging reduced sediment organic carbon (33%), total nitrogen (41%), inorganic nitrogen (18-28%), the abundance of ammonia monooxygenase gene (amoA) (19%), and the ratio of denitrification genes (nirK and nirS) to N₂O-reducing gene (nosZ) (14%). These decreases collectively suppressed the potential N₂O production rates from nitrification (12%) and denitrification (41%), resulting in a 48% reduction in sediment N₂O fluxes and a regulatory shift from denitrification to nitrification dominance. Dissolved organic matter emerged as a pivotal driver linking sediment biogeochemistry to microbial processes, thereby controlling N₂O variability. Dredging also reduced N₂O fluxes at the water-air interface by 41%, with stronger suppression of ebullition (51%) than that of diffusion (30%), establishing diffusion as the dominant emission pathway. Furthermore, reduced substrate availability and functional gene abundances lowered the apparent activation energy of N₂O fluxes by 19% in sediments and 11% at the water-air interface, indicating weakened positive feedbacks to warming. Under simulated eutrophic conditions (2 mg L^-1 TN and 0.2 mg L^-1 TP), dredging offset nearly half of the nutrient-induced increase in N₂O emissions. This study provides mechanistic evidence to support integrated lake management strategies for mitigating N₂O emissions under climate change and eutrophication.