Patrick Verdoux | Université de Nimes (original) (raw)

Papers by Patrick Verdoux

Water research, Apr 1, 2024

Le Centre pour la Communication Scientifique Directe - HAL - Université Paris Descartes, Nov 1, 2021

ABSTRACT Hydro(geo)logical and geochemical approach to investigate the impact of active layer gro... more ABSTRACT Hydro(geo)logical and geochemical approach to investigate the impact of active layer groundwater on runoff in the Austrelovenbreen watershed (Western Spitsbergen - 79°N)

Argillaceous layers are often considered as impermeable formations preventing mi... more Argillaceous layers are often considered as impermeable formations preventing migration of contaminants. Nevertheless, porous and permeable layers in such formation may exist and play a role in contaminant dispersion. The objective here is to investigate the residence time of such porous and permeable layers based on a geochemical and isotopic approach.The study site is located on the Narbonne sedimentary basin, south of France. The Oligo-Miocene argillaceous sedimentary series overlays the cretaceous limestone substratum. A Quaternary deposit partially covers the Tertiary formations. On the western margin the Oligo-Miocene series abuts on the limestone formation. The Oligo-Miocene series is crossed by permeable to semi-permeable layers of conglomeratic deposits, from a few centimetres to a few meters thick, which may represent hydraulic short-circuit. &#160;Groundwater samples from the 3 formations were collected for analyses along with surface water samples, the Aude river, and rain water. The geochemical approach is based on the investigation of time tracers including 3H/3He, 14C and 36Cl/Cl along with the investigation of major and minor elements, stable isotope of water and strontium isotopes.Groundwater conductivity is relatively high ranging from 800 to 2000 &#181;S/cm for the deepest bore hole in the cretaceous formation. Br/Cl and strontium isotope ratio show that groundwater from the permeable layers plot between groundwater from the limestone aquifer and a more mineralised end-member. Groundwater from the permeable layers are slightly depleted in stable isotopes of water with respect to modern precipitation, suggesting recharge under different conditions from the current one. 3H, below detection limit, shows the lack of modern recharge. 14C, in the order of a few pmc, would suggest a residence time of a few ten thousand years. The 36Cl/Cl ratio, in the order of 2x10-14 at/at, is nearly one order of magnitude lower than modern input. Groundwaters from the Oligo-Miocene permeable layers tend to plot on or below a mixing line between recent recharge and a chloride enriched and 36Cl depleted end-member, coherent with long residence time.All tracers are coherent with relatively long residence time and low circulation potential in the porous and permeable layers.&#160;

Anthropogenic contamination, such as agricultural or urban activities, has led i... more Anthropogenic contamination, such as agricultural or urban activities, has led in less than a hundred years to the degradation of the quality of water resources. To assess the vulnerability of groundwater regarding organic and inorganic pollution (i.e. nitrates, pesticides, and pharmaceutical compounds) isotopic tracers may be used. However, in areas where multiple pollution sources occur, isotopic tracers may not be sufficiently discriminant, making source identification difficult. To overcome this problem, a combination of different tracers, including pharmaceutical compounds, along with the multi-isotopic approach is considered. Here, we present the preliminary results of the interpretation of a multi-tracer approach that show a mixed origin of NO3- contamination from agriculture and urban origin as well as the interaction between surface water (Waste-Water Treatment Plant effluent) and groundwater. The multi-tracer approach was applied in the Vistrenque basin area (Gard, France) to characterize NO3- sources. A combination of natural and anthropogenic tracers is implemented, including tracers of water origin (major ions, trace elements (Br, Li, and Sr)), nitrogen and oxygen stable isotopes as a tracer of NO3- (&#948;15N/&#948;18O-NO3-), boron stable isotopes (&#948;11B), water stable isotopes (&#948;18O/&#948;2H-H2O) and strontium isotopes (87Sr/86Sr). In addition, a suite of 80 organic molecules including pesticides and pharmaceutical compounds are trialed as tracers of the origin of the contamination. Analyses were carried out on groundwater samples, surface water, and soil samples to characterize the geochemical and isotopic signature of end-members. The dual-isotope approach &#948;15N/&#948;18O-NO3- for nitrate sources highlights differences between nitrate influenced by nitrification of NH4+ in fertilizer & precipitation origin on one hand, and, nitrates nitrate influenced by manure and septic waste origin on the other hand. However, little contrast between agricultural contamination (i.e. manure) and urban contamination (i.e. sewage) was seen with this method. In parallel, a mixing trend between groundwater and WWTP effluent is evidenced by the combination between &#948;15N-NO3- and &#948;11B. Moreover, this trend is confirmed with the occurrence of pharmaceutical compounds and a positive anomaly in Gadolinium (i.e. contrast-agent) in groundwater. As pharmaceuticals are found in several water supply boreholes the potential of pharmaceutic to discriminate the origin of organic nitrate will be investigated.

Lithos, 2014

This study presents new geochemical data on 26 mafic lavas from the Middle Atlas and Central Moro... more This study presents new geochemical data on 26 mafic lavas from the Middle Atlas and Central Morocco volcanic provinces, including Miocene nephelinites and Pliocene-Quaternary (3.9-0.6 Ma) nephelinites, basanites, alkali and subalkaline basalts. Most of them represent near-primary magmas, although some alkali basalts were derived from the minor fractionation of olivine and diopside phenocrysts. These evolved samples and the subalkaline basalt display higher 207 Pb/ 204 Pb and Zr/Nb ratios and lower εNd consistent with their contamination by lower crustal granulites during an open fractionation process. The progressive enrichment in incompatible elements observed from alkali basalts to nephelinites suggests their derivation from decreasing partial melting degrees of an enriched mantle source located at the garnet-spinel transition zone. The strong negative spikes observed for K in multielement patterns indicate that this source contained a residual pargasitic amphibole. We propose that partial melting occurred at around 2 GPa, i.e. near the lithosphere-asthenosphere boundary beneath the Middle Atlas (60-80 km). The trace element and isotopic Sr-Nd-Pb-Hf signature of the uncontaminated lavas displays a geochemical flavour intermediate between those of high μ (HIMU), "C", and enriched mantle components. It is very similar to that of abundant metasomatic amphibole-and clinopyroxene-rich lithospheric peridotites and pyroxenites carried by Middle Atlas lavas, which likely represent an analog of the source of these lavas. It is therefore not necessary to postulate the contribution of a "fresh" asthenospheric mantle to their genesis. We propose that they resulted from the partial melting of the base of a veined lithospheric mantle metasomatised during the late Cretaceous by alkaline melts from the Central Atlantic plume, the ancestor of the Canary plume. Melting was probably triggered by the flux of a hot mantle within a regional SW-NE sub-lithospheric channel, in response to either the Alboran slab retreat or edge-driven convection around the West African craton.

Hydrology and Earth System Sciences

The increasing severity of hydrological droughts in the Mediterranean basin related to climate ch... more The increasing severity of hydrological droughts in the Mediterranean basin related to climate change raises the need to understand the processes sustaining low flow. The purpose of this paper is to evaluate simple mixing model approaches, first to identify and then to quantify streamflow contribution during low-water periods. An approach based on the coupling of geochemical data with hydrological data allows the quantification of flow contributions. In addition, monitoring during the low-water period was used to investigate the drying-up trajectory of each geological reservoir individually. Data were collected during the summers of 2018 and 2019 on a Mediterranean river (Gardon de Sainte-Croix). The identification of the end-members was performed after the identification of a groundwater geochemical signature clustered according to the geological nature of the reservoir. Two complementary methods validate further the characterisation: rock-leaching experiments and unsupervised classification (k-means). The use of the end-member mixture analysis (EMMA) coupled with a generalised likelihood uncertainty estimate (GLUE) (G-EMMA) mixing model coupled with hydrological monitoring of the main river discharge rate highlights major disparities in the contribution of the geological units, showing a reservoir with a minor contribution in high flow becoming preponderant during the low-flow period. This finding was revealed to be of the utmost importance for the management of water resources during the dry period.

Hydrology and Earth System Sciences Discussions, 2021

Abstract. The increasing severity of hydrological droughts in the Mediterranean basin related to ... more Abstract. The increasing severity of hydrological droughts in the Mediterranean basin related to climate change raises the need to understand the processes sustaining low-flow. The purpose of this paper is to trial simple mixing model approaches first to identify and then quantify streamflow contribution during low-water periods. An approach based on the coupling of geochemical data with hydrological data allows quantifying flow contributions. In complement, monitoring during the low water period was used to investigate the drying up the trajectory of each geological reservoir individually. Data were collected during the summer of 2018 and 2019 on a Mediterranean river (Gardon de Sainte Croix). The identification of the end-members was performed after the identification of groundwater geochemical signature clustered according to the geological nature of the reservoir. Two complementary methods validate further the characterisation: rock leaching experiments and unsupervised classifi...

The analytical precision of the Sr and the Pb isotopic compositions of natural samples obtained w... more The analytical precision of the Sr and the Pb isotopic compositions of natural samples obtained with a conventional ICP-MS is of 3 to 7x10 -3 (internal 2 σ) for the 87 Sr /86 Sr ratio, 6 to 8x10 -3 for the 206 Pb/ 207 Pb and 1 to 4 x 10 -1 for the 206 Pb/ 204 Pb and 207 Pb/ 204 Pb ratios. Such accuracy is obtained with a procedure including a resin-chromatographic purification, a correction with respect to standard values (NBS 987 and 981) and a routine of four determinations for each sample. This procedure should allow rapid geochemical investigations ahead of more precise determinations by thermo-ionization mass spectrometry.

Applied Geochemistry, 2012

Following the explosion of reactor 4 at the Chernobyl power plant in northern Ukraine in 1986, co... more Following the explosion of reactor 4 at the Chernobyl power plant in northern Ukraine in 1986, contaminated soil and vegetation were buried in shallow trenches dug directly on-site in an Aeolian sand deposit. These trenches are sources of radionuclide (RN) pollution. The objective of the present study is to provide constraints for the Chernobyl flow and RN transport models by characterising groundwater residence time. A radiochronometer 3 H/ 3 He method (t 1/2 = 12.3 a) and anthropogenic tracers including CFC and SF 6 are investigated along with the water mass natural tracers Na, Cl, 18 O and 2 H. The groundwater is stratified, as evidenced by Na and Cl concentrations and stable isotopes (18 O, 2 H). In the upper aeolian layer, the Na-Cl relationship corresponds to evapotranspiration of precipitation, while in the underlying alluvial layer, an increase in Na and Cl with depth suggests both water-rock interactions and mixing processes. The 3 H/ 3 He and CFC apparent groundwater ages increase with depth, ranging from 'recent' (1-3 a) at a 2 m depth below the groundwater table to much higher apparent ages of 50-60 a at 27 m depth below the groundwater table. Discrepancies in 3 H/ 3 He and CFC apparent ages (20-25 a and 3-10 a, respectively) were observed during the 2008 campaign at an intermediate depth immediately below the aeolian/alluvial sand limit, which were attributed to the complex water transfer processes. Extremely high SF 6 concentrations, well above equilibrium with the atmosphere and up to 1112 pptv, are attributed to significant contamination of the soils following the nuclear reactor explosion in 1986. The SF 6 concentration vs. the apparent groundwater ages agrees with this interpretation, as the high SF 6 concentrations are all more recent than 1985. The persistence of the SF 6 concentration suggests that SF 6 was introduced in the soil atmosphere and slowly integrated in the groundwater moving along the hydraulic gradient. The apparent age distribution in the lumped parameter models suggests an exponential or piston flow model in the upper geological section, followed by more pronounced mixing processes in the lower section.

Goldschmidt2021 abstracts

Anthropogenic activities can be the source of saline solid wastes that need to be treated to redu... more Anthropogenic activities can be the source of saline solid wastes that need to be treated to reduce their salt load to meet the purposes of reuse, valorization or storage. In this context, chloride remediation can be achieved using high-salt accumulating plants. However, there is very limited information on the comparative potential of different species in the same environment, and only scarce data concerning their efficiency as a function of growth stage. In order to rationalize these selection criteria, three macrophytes i.e. common reed (Phragmites australis), sea rush (Juncus maritimus) and cattail (Typha latifolia) were cultivated at two growth stages (6-months old and 1-year old) for 65 days in Cl- spiked substrates (from 0 up to 24 ‰ NaCl). The plants’ survival and potential capacity for removal of Cl- from substrates and accumulation in shoots were investigated. For the three studied species, mature and juvenile plants display a high tolerance to salinity. However, mature sp...

Water research, Apr 1, 2024

Le Centre pour la Communication Scientifique Directe - HAL - Université Paris Descartes, Nov 1, 2021

Lithos, 2014

Hydrology and Earth System Sciences

Hydrology and Earth System Sciences Discussions, 2021

Applied Geochemistry, 2012

Goldschmidt2021 abstracts