Hydraulic and geochemical impact of occasional saltwater intrusions through a submarine spring in a karst and thermal aquifer (Balaruc peninsula near Montpellier, France)

Abstract

Abstract. Submarine springs are a common discharge feature of the karst aquifers along the Mediterranean coast. In some instances, occasional and localized saltwater intrusions can occur through the submarine spring and negatively impact the quality of the groundwater resource. The hydraulic and geochemical behaviour of a submarine spring discharging into the Thau Lagoon just offshore of the Balaruc peninsula near Montpellier, France, has been characterized to determine the impacts of such phenomena to better understand the dynamics of a regional karst aquifer and improve its groundwater management. This work is based on both historical and new hydrogeological and geochemical data, illustrating six occasional saltwater intrusion events (from 1967 to 2014) in the Thau Lagoon area (southern France). Hydraulic perturbation of the aquifer is propagated instantly within the Balaruc-les-Bains peninsula and reaches a distance of about 5 km upgradient within 9 d. Comparison of hydraulic heads during seawater intrusion events in 2010 and 2014 indicates an aggravation of the phenomenon with an increase in hydraulic head variations. In contrast, isotopic tracers (87Sr∕86Sr, D/H, 18O∕16O) and rare earth elements (REEs) demonstrate that the geochemical impact of these inversac events is only observed at the local scale but is still perceptible several years after the event. For example, some of the thermal wells had not recovered their initial geochemical state 20 and 40 months after the last two inversac events (2010 and 2014, respectively), suggesting a geochemical legacy of this phenomenon within the complex karst system. By contrast, an adjacent deep karst compartment located south of the study area is not affected by the saltwater intrusion and is characterized by distinctly different hydrodynamic behaviour. Overall, this work on occasional and localized saltwater intrusions constitutes a key step in understanding the dynamics of this complex karstic and thermal aquifer and will support the management of the groundwater resource.

Coastal karst aquifers and submarine springs: what future for their water resources?

“…This study highlights the importance of monitoring for characterizing the salinization phenomenon in coastal karst aquifers. The same approach was applied at two coastal karsts in the south of France: the karst aquifer of Aumelas discharging into the Thau Lagoon [Pétré et al, 2020] and the Eastern Corbières aquifer, both located to the West of Montpellier. These aquifers are instrumented with salinity, temperature and groundwater level data loggers to assess the seawater intrusion, as part of a research project conducted by the French Geological Survey (BRGM).…”

Dataset on onshore groundwaters and offshore submarine spring of a Mediterranean karst aquifer during flow reversal and saltwater intrusion

“…This dataset was generated to study the behavior of a Mediterranean coastal (lagoon) karst aquifer for which the flow reversal phenomenon has occurred several times in the past through a submarine karst spring. The equipment and the monitoring of the submarine spring constitute a key element of the research project to understand of the hydrogeological functioning of the karst system during regular conditions, when fresh groundwater flows out of the submarine spring, as well as during disruptive events, when flow reversal and salty water intrusion through the spring occur [5] , [6] , [7] .…”

Impact of connected conduit on pumping-induced seawater intrusion in a coastal karst aquifer

“…During the last decade, researchers have given significant attention to this issue (e.g., Bakalowicz, 2018;Acikel and Ekmekci, 2021;Fleury et al, 2023;Schuler et al, 2019), conducting numerous numerical simulations, lab and field experiments to understand the process of seawater-fresh water interactions, assess aquifer vulnerability, and further apply to the geochemical and nutrient investigations (e.g. Faulkner et al, 2009;Xu et al, 2015;Oehler et al, 2019;Bejannin et al, 2020;Petréet al, 2020;Shokri et al, 2022).…”