Strontium isotope geochemistry of alluvial groundwater: a tracer for groundwater resources characterisation

International audience(Paris, 29 septembre 2011, n° 2010/24176, X c/ AMF., D. 2012. 204, note D. Martin et M. Françon

Application of multi‑method approach to assess groundwater–surface water interactions, for catchment management

Globally, the dependence of river systems to delayed discharge of subsurface water to augment flows during dry seasons is well documented. Discharge of fresh subsurface water can dilute concentrated river flow quality during reduced flow. Observed and reported results on the Berg River’s declining water quantity and quality are a concern to the regions socio-economic growth and environmental integrity. Understanding the role of subsurface water discharges on the quantity and quality of receiving surface water courses can improve their management during dry periods. A case study was designed and implemented in the upper Berg River catchment in the Western Cape Province of South Africa to assess the influence of groundwater–surface water interaction on water quantity and quality. This study aimed to quantify and characterize the quality of subsurface water available in the upper catchment to improve observed declining water quality downstream. Hydrograph separation provided estimates of water fluxes during 2012–2014 low and high flow periods, while hydrochemical analysis provided insights on impacts of major land use activity in this catchment on water resources. Hydrograph separation analysis indicated that the Berg River is 37.9% dependent on subsurface water discharges annually. Dominant Na–Cl-type water indicates the quality of water from the upper Berg River is largely affected by natural processes including short residence times of aquifer water, rock–water interactions and atmospheric deposition of NaCl ions. These results provide insights for suggesting management options to be implemented to protect subsurface water for continued dilution and water resources management in the lower catchments

Strontium isotope geochemistry of alluvial groundwater: a tracer for groundwater resources characterisation

This study presents strontium isotope and major ion data of shallow groundwater and river water from the Ile du Chambon catchment, located on the Allier river in the Massif Central (France). There are large variations in the major-element contents in the surface- and groundwater. Plotting of Na vs. Cl contents and Ca, Mg, NO₃, K, SO₄, HCO₃, Sr concentrations reflect water–rock interaction (carbonate dissolution for Ca, Mg, HCO₃ and Sr because the bedrock contains marly limestones), agricultural input (farming and fertilising) and sewage effluents (for NO₃, K, SO₄), although some water samples are unpolluted. Sr contents and isotope ratios (⁸⁷Sr/⁸⁶Sr vary from 0.70892 to 0.71180 along the hydrological cycle) in the groundwater agree with previous work on groundwater in alluvial aquifers in the Loire catchment. The data plot along three directions in a ⁸⁷Sr/⁸⁶Sr v. 1/Sr diagram as a result of mixing, involving at least three geochemical signatures–Allier river water, and two distinct signatures that might be related to different water-rock interactions in the catchment. Mixing proportions are calculated and discussed. The alluvial aquifer of the Ile du Chambon catchment is considered, within the Sr isotope systematic, in a larger scheme that includes several alluvial aquifers of the Loire Allier catchment.</p> <p style='line-height: 20px;'><b>Keywords: </b>: Loire river, major and trace elements, Sr isotopic ratio, alluvial aquifer, hydrolog

Surface water–groundwater interactions in an alluvial plain: Chemical and isotopic systematics

International audienceOur work on the Loire River forms part of a French National Research Program dedicated to wetlands and aims to better understand the global functioning of the system from the hydrological, geochemical, ecological and sociological aspects. The present study, using a coupled hydrological and geochemical (stable and Sr isotopes) approach, focuses on the ‘Soulangy’ site with its secondary anastomosing channels just below the confluence of the Loire and Allier rivers, and also on the ‘Dorna``nt’ site with two unconnected oxbow lakes 50 km upstream of the confluence. The stable isotopes of water (δ18O, δ2H) show that the alluvial (or riverbank) aquifer feeds the Loire River during the summer, but is not recharged by the river during flood periods in the winter; the alluvial groundwater thus has a purely local origin from precipitation. The major elements reveal an anthropogenic input of Cl and more importantly of NO3, especially near farms. The 87Sr/86Sr isotopes identify different groundwater layers in the alluvium, i.e. an upper and a lower alluvial aquifer, and a perched aquifer at Dornant, that have relatively complex relationships with the surface water. The two main rivers (Loire and Allier) present distinct geochemical characteristics reflecting the different lithologies that they drain upstream. In addition, the secondary channels, lying parallel to the Loire main stream at the Soulangy site, give different geochemical signatures, which shows that they are not fed by the same overflows of the Loire; they are more-or-less well connected to the upper level of the alluvial plain, and a longitudinal study of one of these channels has revealed a Loire River influence progressively replaced by a water contribution from the upper alluvial aquifer. Similarly, the two oxbow lakes at the Dornant site are not supplied by the same water during the summer months. A conceptual scheme of the Loire hydrosystem based on δ18O and 87Sr/86Sr suggests that the isotopic variations of the Loire River can be related to a Massif Central surface-water supply for the Loire and Allier main streams and to a groundwater supply from the alluvial plains

Reinforcing the origin of volcanic rocks from the Massif Central through the isotopic composition of lead and strontium

International audienceThe Massif Central in France hosts a large volume of Tertiary to Recent continental alkaline volcanism, with evidence of crustal contamination of the differentiated magmas. Detailed investigations on feldspathic basalts and basanite rocks from the Cantal volcano exposed in the Allanche basin by lead and strontium isotopes reveal i) the role of the mantle components Depleted Mantle (DM) and Low Velocity Component (LVC, corresponding to the European asthenospheric reservoir) end-members based on 208Pb/204Pb and 206Pb/204Pb isotopic ratios, and ii) show contamination by meta-igneous granulites from the lower crust when using 207Pb/204Pb vs. 206Pb/204Pb ratios, as only part of the samples plot along the Northern Hemisphere Reference Line (NHRL) mixing line between DM and HIMU (High U/Pb Mantle) end-members. Cross plotting of Pb-Sr isotopes rules out recycled sediment and/or igneous granulite as potential crustal contaminant for the Cantal basalts, but suggests mixing between the low-velocity component LVC and EMI (Enriched Mantle I)-pelagic sediments. Replaced in the regional context of the Massif Central, we confirm the existence of several mantle sources and different crustal contaminations in the magmas of the Cantal volcan

Mobility, turnover and storage of pollutants in soils, sediments and waters : achievements and results of the EU project AquaTerra : a review.

AquaTerra is one of the first environmental projects within the 6th Framework program by the European Commission. It began in June 2004 with a multidisciplinary team of 45 partner organizations from 13 EU countries, Switzerland, Serbia, Romania and Montenegro. Results from sampling and modeling in 4 large river basins (Ebro, Danube, Elbe and Meuse) and one catchment of the Brévilles Spring in France led to new evaluations of diffuse and hotspot input of persistent organic and metal pollutants including dynamics of pesticides and polycyclic aromatic hydrocarbons, as well as metal turnover and accumulation. While degradation of selected organic compounds could be demonstrated under controlled conditions in the laboratory, turnover of most persistent pollutants in the field seems to range from decades to centuries. First investigations of long-term cumulative and degradation effects, particularly in the context of climate change, have shown that it is also necessary to consider the predictions of more than one climate model when trying to assess future impacts. This is largely controlled by uncertainties in climate model responses. It is becoming evident, however, that changes to the climate will have important impacts on the diffusion and degradation of pollutants in space and time that are just at the start of their exploration

Selected groundwater studies of EU project AquaTerra leading to large-scale basin considerations

Several local groundwater studies within the EU project AquaTerra in the Basins of the Meuse, Elbe point at significant influences of groundwater on surface water, while the Brévilles Catchment shows a distinct problematic of pesticide loading to groundwater. Further modeling studies are currently being developed. In the Danube Basin no specific groundwater studies were carried out in the framework of AquaTerra. However on larger scales geochemical proxies such as strontium isotope ratios can give an insight into groundwater contributions to the river that reflects an integral signal of the environmental status of the Basin. Future local groundwater studies should be further correlated to the environmental status of rivers nearby

Selected groundwater studies of EU project AquaTerra leading to large-scale basin considerations

Several local groundwater studies within the EU project AquaTerra in the Basins of the Meuse, Elbe point at significant influences of groundwater on surface water, while the Brévilles Catchment shows a distinct problematic of pesticide loading to groundwater. Further modeling studies are currently being developed. In the Danube Basin no specific groundwater studies were carried out in the framework of AquaTerra. However on larger scales geochemical proxies such as strontium isotope ratios can give an insight into groundwater contributions to the river that reflects an integral signal of the environmental status of the Basin. Future local groundwater studies should be further correlated to the environmental status of rivers nearby.AquaTerra EU Project FP6 Project no. 505428 (GOCE