Jean-Luc Seidel

Occurrence of an anthropogenic gadolinium anomaly in river and coastal waters of Southern France

This study reports a pronounced positive Gd anomaly in a small river and in the largest French Mediterranean lagoon. Along the studied catchment, this anomaly is also present in the effluents of the municipal sewage treatment plants, suggesting an anthropogenic origin for the Gd excess. The anomaly corresponds to a distinct increase of Gd concentrations (up to 19 pmol/l) in the river and around 5.4 pmol/l in the lagoon. The excess flux of Gd is compatible with the medical use of water soluble Gd complexes as contrasting agent in magnetic resonance imaging.

Positive gadolinium anomalies in wastewater treatment plant effluents and aquatic environment in the Hérault watershed (South France).

Anthropogenic gadolinium (Gd), used as a contrast agent in magnetic resonance imaging, may enter rivers and groundwaters with the effluents of wastewater treatment plant (WWTP). Such contaminations, which are mainly found in densely populated areas with highly developed medical systems, induce positive gadolinium anomalies in waters. This study reports on the occurrence of positive Gd anomaly in wastewaters, surface and groundwaters in a slightly populated Mediterranean watershed. Water samples have been collected along the Hérault River, in its tributaries, in wells and springs supplying drinking water and in WWTP effluents during two sampling campaigns in February and July 2003. Systematically pronounced positive gadolinium anomalies (Gd/Gd( *)) were observed in WWTP effluents with values reaching 306. These observations have shown that Gd/Gd( *) can also be found in wastewater drained from rural communities, not equipped with MRI facilities. Positive gadolinium anomalies were detected in two tributaries of the Hérault River and in some wells supplying drinking water, corresponding to an excess of anthropogenic Gd in water up to 15.4pM. A monthly monitoring on one well has confirmed the persistence of gadolinium anomalies all along the year, suggesting a continual wastewater contamination on this site. A spatial monitoring on one tributary showed that wastewater contribution modifies completely the normalized REE pattern of river water, resulting in a decrease of REE amount correlated to the Gd anomaly appearance.

Seasonal variations of CO 2 and 222 Rn in a mediterranean sinkhole - spring (Causse d’Aumelas, SE France)

INTRODUCTION Carbon dioxide dynamics and transfer from soil to the deepest parts of an aquifer underlie the main karstification processes. Cavity ventilation plays an important role in speleothem formation and chemical equilibrium of water in the unsaturated zone of the aquifer. Meteorological parameters (barometric pressure and temperature), cave geometry and fracture networks control exchanges between subterranean and outside atmosphere (De Freitas et al., 1982; De Freitas & Littlejohn, 1987; Smithson, 1991; Christoforou, 1996; Buecher, 1999; Fernandez-Cortes, 2005). Gases currently studied in caves are CO2 and 222Rn. Their concentrations and variations can be explained by different parameters. Carbon dioxide concentrations in cavities vary from 0.03 % to more than 6 % and may have different sources : Batiot-Guilhe C., Seidel J.L., Jourde H., Hébrard O., Bailly-Comte V. 2007. Seasonal variations of CO2 and 222Rn in a Mediterranean sinkhole spring (Causse d’Aumelas, SE France). International Journal of Speleology, 36 (1), 51-56. Bologna (Italy). ISSN 0392-6672.

Shock wave radon surface signals associated with the upsurge of T-P solitons in volcanic systems

Abstract The present paper introduces a theoretical model in order to describe ground surface anomalies of radon emissions as a volcano is perturbed from its quiescent (steady) state. Based upon modern thermo-poro-elasticity theory which has been found to successfully explain rock deformation-fracturing, these anomalies are considered as being due to the build up of a buried thermo-mechanical source which in turn gives rise to the upsurge of a thermo-mechanical (or T-P) soliton. This sort of fluid solitary wave, travelling upwards through induced deformed–fractured horizons, locally perturbes a pre-existing stationary radon concentration profile as the wave approaches the ground surface. In order to model radon anomalies, a diffusive–convective transport equation of radon is adopted with Darcys velocity change controlled by the upsurge of the T-P soliton. As a result, a new flow mechanism of radon emission is found, which we call shock wave radon propagation. Some cases of volcanic eruptions which have been preceded and accompanied by anomalies in radon emissions are examined in the light of the model. A reasonably good agreement in the pattern between the observed radon concentration changes and the theoretical curves is found. A theoretical tool for volcanic surveillance is thus proposed, corresponding to both an effort to shed more light on the correlations that may exist between geophysics and geochemistry of fluid emissions and the recognition, through ground surface radon anomalies, of subsurface thermo-mechanical instabilities possibly preceding volcanic eruptions.

Characterisation of rapid infiltration flows and vulnerability in a karst aquifer using a decomposed fluorescence signal of dissolved organic matter

Abstract The fluorescent properties of dissolved organic matter (DOM) have been used as natural tracers in various water systems. However, only few studies have focused on groundwater systems, specifically, on karst systems. The aim of this study was to develop the use of the DOM fluorescence signal as a natural tracer, considering the multiple compartments of a karst system. This method was applied to the Lez hydrosystem, which supplies the city of Montpellier with drinking water. The hydrodynamics and hydrochemistry of the spring were monitored beginning March 2006. The DOM fluorescence was measured by the excitation–emission matrix spectroscopy technique. The analysis of the total fluorescence signal confirms the efficiency of this tool to trace rapid infiltration flows. Moreover, the decomposition of the signal into different fluorophores complements the information provided by the total signal. Indeed, the fluorescence emitted by the humic compounds seems to be the ideal tool for identifying rapid infiltration flows. Nevertheless, the fluorescence of protein-like compounds is better correlated with the inflow of faecal bacteria at the outlet. This decomposition of the fluorescence signal is an interesting way to provide information on both the rapid infiltration flow as well as the vulnerability of the karst aquifers.

Trace-Metal Biogeochemistry in the Mediterranean Thau Lagoon, a Shellfish Farming Area

Abstract The present study contributes to the knowledge of the biogeochemistry of Pb, Cd, Cu, and Ni in the Mediterranean Thau Lagoon, southern France, which is an important shellfish farming system. The concentrations of the metals were determined in sediment cores and the overlying waters using inductively coupled plasma mass spectrometry. Particular attention was given to the determination of dissolved Cu species because of their dual role as essential nutrient and toxicant to planktonic organisms. Dissolved Cu speciation was determined using the diffusive gradient in thin-film technique (DGT) and competitive ligand exchange–adsorptive cathodic stripping voltammetry (CLE-ACSV). Our data indicated a significant historical contamination of the sediments, which commenced in the second half of the 19th century, with trace metal inputs persisting until the end of the 20th century. In recent years a decrease in metal contamination has become apparent. The maxima observed for Pb, Cd, and Cu profiles probably indicate the occurence of anoxia crises. A strong complexation of the dissolved Cu species was observed in the waters of the Thau Lagoon, which reduced the bioavailability of Cu. The dissolved Cu2+concentrations were probably too low to cause direct toxic effects on shellfish, but the highest concentration (5.29 pM) observed in this study can potentially influence phytoplankton communities. A comparison between the Cu speciation data indicates that up to 50% of the complexed Cu determined using CLE-ACSV was DGT labile.

Investigation of Groundwater Dynamics in a Mediterranean Karst System by Using Multiple Hydrogeochemical Tracers

The Lez karst aquifer, located in southern France, supplies the Montpellier metropolitan area with potable water and has a maximum exploitation capacity of about 1.700 L/s. The objective of this work is to improve the comprehension of groundwater dynamics in a particular Mediterranean karst system, using hydrogeochemical tracers. The different types of groundwater with similar chemical characteristics (major and trace elements) are identified. During rainy season periods, this multitracer characterization shows that deep mineralized waters emerge at the springs just before rapid infiltration waters. This phenomenon shows that hydrodynamic conditions imply water circuits, with participation of specific compartments or creation of short cuts for superficial percolating waters. The data also highlight the vulnerability of the system to natural or anthropogenic contamination. Key words: karst, hydrochemistry, natural tracing, hydrodynamics.

Quality of water resources in the Niger basin and in the region of Lagos (Nigeria)

Abstract Water quality studies in Nigeria are usually conducted at local scales and limited to a restricted number of chemical contaminants, while reliable data on trace metal concentrations (including arsenic) are relatively scarce. This study focuses on the quality of available renewable water resources in terms of major ion and trace element concentrations at selected sampling locations in the Lower River Niger basin and part of the Lagos region. A screening of water contamination by arsenic and heavy metals was carried out through water sampling at selected locations using in situ measurement and laboratory testing to estimate heavy metal concentrations and water type. The analysis reveals moderate trace element contamination of the water resources, with the exception of Pb, while Mn and, to a lesser extent, Al exceeded WHO quality standards, but the Arsenic concentrations are within drinking water quality standards and are safe for consumption and irrigation, while the water type is Bicarbonate.