Enhanced submarine groundwater discharge and nutrient fluxes in response to typhoon events in Zhanjiang Bay, China.

Typhoons significantly influence the spatiotemporal dynamics of submarine groundwater discharge (SGD) and associated nutrient fluxes in coastal systems. This study investigates the impact of multiple typhoon events of Typhoons Lionrock and Kompasu on the distribution of 222Rn and SGD in Zhanjiang Bay, South China, and evaluates the consequent variations in nutrient (DIP, NO2- + NO3-, DSi) inputs via SGD. Results show that typhoons induce a substantial increase in SGD fluxes, with peak post-typhoon values reaching up to 8 times pre-typhoon levels, primarily driven by intense rainfall that enhances the inland hydraulic gradient and recharges coastal aquifers. The spatial pattern of 222Rn activity shifts from weak pre-typhoon salinity correlation to a strong negative correlation post-typhoon, indicating a dominant contribution of low-salinity, freshwater SGD. Despite significant spatial variability in 222Rn, zonal analysis confirms that SGD rates in Zhanjiang Bay fall within the global typical range, with slightly higher values likely due to coarse-grained sediments enhancing permeability. Nutrient fluxes via SGD increase dramatically after typhoons, with DSi, DIP, and NO2- + NO3- fluxes rising by 46.54 %, 119.56 %, and 47.51 %, respectively, during the peak event. DSi and NO2- + NO3- exhibit conservative behavior and strong correlation with SGD, whereas NO2- + NO3- dynamics are complicated by active microbial processes. Notably, SGD-derived nutrient inputs during typhoons may act as the primary driver of nutrient loading and a critical factor in the potential eutrophication of Zhanjiang Bay.