Extreme precipitation events induce high fluxes of groundwater and associated nutrients to coastal ocean

Current studies of submarine groundwater discharge (SGD) are commonly conducted under aquifer baseflow conditions, neglecting the influence of episodic events that can significantly increase the supply of nutrients and water. This limits our understanding of the social, biogeochemical, and ecological impacts of SGD. In this study, we evaluated the influence of an extreme precipitation event (EPE) on the magnitude of SGD. To do so, three seawater sampling campaigns were performed at a Mediterranean ephemeral stream-dominated basin after an EPE (similar to 90 mm in few hours) and in baseflow conditions. Results indicate that the groundwater flows after the EPE were 1 order of magnitude higher than those in baseflow conditions. The SGD induced by EPEs, which only take place a few days per year, represented up to one third of the annual discharge of groundwater and associated nutrients at the study site. This work accentuates the need to account for episodic increases in the supply of water and nutrients when aiming to provide reliable annual SGD estimates, particularly in the current context of climate change, since the occurrence of such events is expected to increase worldwide.