# How to discriminate between local and regional flows for the management of karst groundwater resources? Use of δ2H vs δ18O applied to the Huveaune watershed and the hydrogeological catchment of the Port-Miou spring, southeastern France)

Bruno Arfib, Thibaut Garin, Bernard Ladouche, Julio Goncalves, Benoît Dewandel, Thierry Lamarque

► To cite this version:

Bruno Arfib, Thibaut Garin, Bernard Ladouche, Julio Goncalves, Benoît Dewandel, et al. How to discriminate between local and regional flows for the management of karst groundwater resources? Use of δ2H vs δ18O applied to the Huveaune watershed and the hydrogeological catchment of the Port-Miou spring, southeastern France. 4. Eurokarst Conference (EUOKARST 2024), Jun 2024, Roma, Italy. 2024. [hal-04845612](https://hal.science/hal-04845612v1)

HAL Id: hal-04845612

https://hal.science/hal-04845612v1

Submitted on 20 Dec 2024

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# How to discriminate between local and regional flows for the management of karst groundwater resources?

## Use of δ²H vs δ¹⁸O applied to the Huveaune watershed and the hydrogeological catchment of the Port-Miou spring (SE France)

Bruno Arfib¹, Thibaut Garin¹, Bernard Ladouche²,³, Julio Goncalves¹, Benoit Dewandel²,³, Thierry Lamarque⁴

(1) Aix-Marseille Université, OSU PYTHEAS, CEREGE, CNRS, IRD, INRAE, Marseille - Aix en Provence, France, Email: arfib@cerege.fr, www.karsteau.fr

(2) BRGM, D3E/NRE-University of Montpellier, 1039 rue de Pinville, 34000 Montpellier, France

(3) G-eau, UMR 183, INRAE, CIRAD, IRD, AgroParisTech, Institut Agro, BRGM, Montpellier, France

(4) Spélé-H2O association, Six-Fours, France,

## Challenges and goals

* Define river watershed and groundwater recharge zones

* Discriminate between local and regional groundwater flows

* Define groundwater δ¹⁸O, δ²H end-members

* Propose to water managers a tool to identify the groundwater origin

<figure><img src="image_2.png" /></figure>

<figure><img src="image_3.png" /><figcaption>Huveaune river</figcaption></figure>

<figure><img src="image_4.png" /></figure>

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<figure><img src="image_6.png" /></figure>

## Context and case study

* Mediterranean karst aquifers

* Deep and multi-phased karstification (Messinian salinity crisis and plioquaternary eustatic variations)

* Regional groundwater flow disconnected from surface flow : major freshwater resource and limited impact on surface water ecology

* High range of elevation (from the sea to 1148 m asl)

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /></figure>

* Carbonate rocks from Trias, Jurassic, Cretaceous and Oligocene ages

* Surface watershed (Huveaune) discharging to the West

* Regional groundwater flow discharging to the South at the Port-Miou submarine spring (recharge area ≈400 km²)

* Inflow of external freshwater from the Alps for water supply (surface channel transfers)

## Method

* 23 water sampling points (river, spring, borehole)

* 97 analyses, under a variety of hydrological conditions (low-water, flood, base-water, high-water) between 2018 and 2020

* Major ions

* δ¹⁸O, δ²H (Picarro, Univ. Montpellier, Univ. Marseille, uncertainty <0.15‰ for δ¹⁸O and < 1.5‰ for δ²H)

## Results

Stable isotopes range :
≈ -7.8 to -6.6 ‰ δ¹⁸O
≈ -50 to -39 ‰ δ²H

<figure><img src="image_9.png" /></figure>

Selection of points with very low range of variation (<0.2‰ δ¹⁸O): potential regional end-members

<figure><img src="image_10.png" /></figure>

High range of variation = influence of rainfall quickly infiltrated or mixing from various origins

<figure><img src="image_11.png" /></figure>

Evaporation effect on Huveaune river samples. Groundwater mixing with external depleted water (surface channels)

<figure><img src="image_12.png" /></figure>

## A graphical tool for water management

Several end-members identified for regional groundwater flows

<figure><img src="image_13.png" /></figure>

### • Advantages :

* In situ sampling easy to proceed

* Low cost analysis

* New sampling points (e.g. new boreholes) can be immediately added to the database

* Method adapted to highlight points influenced by rapid infiltration (risk of rapid transfer of pollutant)

* Offers a long-term monitoring of the water cycle

* Data useful for climate change studies

### • Requires :

* An isotopic contrast between local and regional groundwater (elevation, surface water evaporation, water from external catchment area...)

* Sampling in different hydrological conditions

* Sampling many springs, boreholes and rivers at regional scale to characterize the spatial and temporal variations

Acknowledgements: SPL Eau des collines, SIBAM, SEM, Bronzo Perasso, ANTEA, ONF, Météo-France, PNR Sainte-Baume, PN Calanques

<figure><img src="image_14.png" /></figure>