Surface Nuclear Magnetic Resonance Monitoring Reveals Karst Unsaturated Zone Recharge Dynamics during a Rain Event

Abstract

Understanding karst unsaturated zone (UZ) recharge dynamics is crucial for achieving sustainable management of karst hydrosystems. In this paper, we provide the first report of the application of surface nuclear magnetic resonance (SNMR) monitoring of a karst UZ during a typical Mediterranean rain event. This 79 days’ SNMR monitoring is a part of a more than 2 years of SNMR monitoring at the Low Noise Underground Laboratory (LSBB) experimental site located within the Fontaine de Vaucluse karst hydrosystem (southeastern France). We present eight SNMR soundings conducted before and after the rain event that accumulated 168 mm in 5 days. The obtained results demonstrate the applicability and the efficiency of SNMR for investigating infiltration dynamics in karst UZs at the time scale of a few days. We present the SNMR amplitudes that highlight strong signal variations related to water dynamics in the karst UZ. Infiltrated water cause increased SNMR signal during 5 days after the rain event. A significant draining process of the medium starts 15 days after the main event. Finally, after 42 days, the SNMR signal returns close to the initial state.

Monitoring unsaturated water flow using magnetic resonance soundings

“…Our data do not show fast water flow during and immediately after heavy rain events reported by Mazzilli et al, (2020). In order to better analyze large and small rainfall effects, and provide the necessary constrains to what appears as a non-linear flow modelling, we recommend a dense sampling rate during intensive rainfall events.…”

“…When not saturated, this formation has a low storage capacity, which could explain the MRS results. Indeed, Mazzilli et al (2020) report the MRS monitoring of a heavy rain event in a karst environment. The authors observed a large MRS signal only during a few days after the rain event.…”

First Evidence of Correlation Between Evapotranspiration and Gravity at a Daily Time Scale From Two Vertically Spaced Superconducting Gravimeters

“…The upper formations (≈300 m thick; Figure 1) are lower Aptian/upper Barremian sub‐reef limestones (Masse & Fenerci‐Masse, 2011) with high porosities (5%–20% in the study area, Léonide et al., 2014). Seasonal variations in water content, measured by MRS (magnetic resonance sounding), revealed the strong capacitive hydrogeological role of this limestone (Carrière et al., 2016; Mazzilli et al., 2020). The underlying formations are lower Barremian limestones with significantly lower porosities (<5%; Guglielmi, 2010; Masse, 1969).…”

Multi-geophysical Field Measurements to Characterize Lithological and Hydraulic Properties of a Multi-scale Karstic and Fractured Limestone Vadose Zone: Beauce Aquifer (O-ZNS)

“…Development of multi-channel instruments has also allowed to access from 1D to 2D and 3D measurements [43]. Although the poor signal to noise ratio limits this method [42], it has proven its efficiency for limestone VZ and karstic aquifer characterization [7,[45][46] -Seismic refraction methods [47][48][49] are best applied to the characterization of tabular objects such as soil layers or horizontal cracks [5]. They also provide insights into water saturation for groundwater modeling [47] or into deep formations [39].…”