Abstract

Current Submarine Groundwater Discharge (SGD) studies 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 both the terrestrial and marine components of SGD. To do so, three seawater sampling campaigns were performed at a Mediterranean ephemeral stream-dominated basin after an extreme precipitation event (~90 mm in few hours) and in baseflow conditions. Results indicate that the groundwater flows of terrestrial and marine SGD after the extreme precipitation event were 1 order of magnitude higher than those in baseflow conditions. SGD induced by extreme precipitation events, 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 at providing reliable annual SGD estimates, particularly in the current context of climate change, since the occurrence of such events is expected to increase worldwide.

Highlights

  • Submarine groundwater discharge (SGD) - the flow of terrestrial and marine groundwater to the coastal ocean - is one of the 25 primary processes regulating the transfer of solutes from land to ocean (Santos et al, 2021)

  • As inferred by 140 electric resistivity tomography profiles shown in Palacios et al (2019), conductivity variations in the piezometric wells of the study site were not derived from dilution with low-conductivity rainwater, but associated with the movement of the mixing zone due to extreme precipitation event (EPE)

  • The mean sea level (MSL) presented oscillations linked to the EPE, which are usually associated with atmospheric fronts and strong winds, and 145 to seasonal meteorology, with higher MSL values from October to December than from January to April

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Summary

Introduction

Submarine groundwater discharge (SGD) - the flow of terrestrial and marine groundwater to the coastal ocean - is one of the 25 primary processes regulating the transfer of solutes from land to ocean (Santos et al, 2021). The significance of this process at local, regional and global scale stems mainly from its role in modulating the water and chemical budgets of oceans, controlling coastal ecosystems, and contributing to the well-being of coastal societies (Alorda-Kleinglass et al, 2021; Lecher et al, 2015; Luijendijk et al, 2020).

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