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.