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

Abstract

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.

High spatial heterogeneity and low connectivity of bacterial communities along a Mediterranean subterranean estuary

“…In turn, very few of the aquifer taxa were also detected in marine waters, suggesting that at least during the sampling period (summer), there is little microbial dispersal between aquifer and marine communities. This transport of microorganisms from the aquifer to the sea might, however, be enhanced in the wet season when groundwater discharge increases, as extreme precipitation episodes typical of spring and autumn in the study site have shown to increase SGD by 1 order of magnitude compared to baseflow conditions (Diego‐Feliu et al, 2022 ). Regardless of whether dispersal of taxa between the surface, the aquifer and the sea may shape microbial structure and functioning, our data suggest that strong selection by local conditions is the main process structuring the Argentona microbiome, at least during baseflow conditions.…”

“…Other prokaryotic groups showed more gradual changes along the salinity gradient, being more prevalent in the fresher portions of the aquifer (Burkholderiales, Nitrospirota, Planctomycetota), or preferring brackish (Gamma‐ and Alphaproteobacteria) or saline sites (Bacteroidota and Campylobacterota). This means that hydrological changes, such as variations in the extent of the saline intrusion (Folch et al, 2020 ; Palacios et al, 2020 ) or the occurrence of extreme precipitation events (Diego‐Feliu et al, 2022 ), may trigger major changes in the physicochemical parameters of the subterranean estuary and thus impact communities and their associated metabolic functions. For example, increases in salinity have been associated with decreased denitrification, nitrification and anammox (anaerobic ammonium oxidation, Jiao et al, 2018 ; Santoro, 2010 ).…”

Organic matter composition and inorganic nitrogen response to Hurricane Harvey’s negative storm surge in Corpus Christi Bay, Texas

“…Short bursts of remineralized and terrestrially derived inorganic nitrogen, via subterranean inputs, such as SGD found to increase following Hurricane Harvey in the adjacent Nueces Bay and Upper Laguna Madre (Murgulet et al, 2022), are a plausible cause for the observed trends. Other recent studies found storm events responsible for higher SGD rates and nutrient fluxes to the coastal ocean, although these occurrences were mostly driven by high precipitation rates and subsequent recharge (McKenzie et al, 2021;Diego-Feliu et al, 2022).…”