Climate Change Impact on the Mineralization of Karst Groundwater in a Mediterranean Context

International audienc

Use of mixing models to explain groundwater quality time and space variation in a narrowed fluctuating alluvial aquifer

International audienceHydrogeochemical studies can provide insights to pursue a flexible and responsive groundwater resources management.Origin of water, mixing and reactive processes are three key parameters that allow to understand hydrological systems and resulting groundwater quality.However, those parameters may evolve strongly and quickly over time and space, especially for hydrological system impacted by pumping activities and seasonal variations.Within this framework, the current study aims to pursue a survey of the hydrological parameters in a small dynamic alluvial aquifer fed by 3 contrasted end-members and used for water supply.The variations of the end-members and the alluvial groundwaters quality (Ca2+, Mg2+, K+, Na+, Cl− , CO3 2− , NO3 − , δ2H and δ18O) will be used as a record of those parameters. 26 sampling campaigns were carried out fortnightly from October 2017 to October 2018 and data processed with two distinct mixing models: GLUE-EMMA model, which define likelihood of each mixing component, and PHREEQC inverse modeling, which account for the reactive processes that occur as water chemistry evolves. For each studied groundwater, appropriate time variant end members signatures as well as analytical uncertainties were accounted and models constrained to fit within 5.0% for the major ions and 0.5‰ for water stable isotopes.With suitable models for all alluvial groundwater samples, both GLUE-EMMA and PHREEQC highlight the mixing process between two end-members as the main parameter of the alluvial groundwater quality. Nonetheless, Mg2+ and K+ reactive fluxes are needed to fit with the required constraints.Hence, the alluvial groundwater quality variations are either associated with the typical seasonal variations of the end-member signature and the change of the mixing processes.For both models, mixing process exhibits slow and small as well as strong and sudden changes. The first can be related with the relative capacity of the end members to feed the aquifer according to their individual high and low water periods. The second to the effects of alternative pumping regime between sampling campaign.The capacity of both models to evaluate and monitor main hydrological processes, over time and space, confirms the interest to combine them as a flexible multi process investigation suited for dynamic hydrological system

Water stable isotopes and volumetric discharge rates to monitor the Rhône water's seasonal origin

International audienceAlong the 98 800 km 2 Rhône catchment area, 3 million people depend on the river resource and its sustainability. Flow rate monitoring of the French rivers showed the importance of the Swiss part of the Rhône (measured at station 1), the Isere (station 2) and the Durance rivers (station 3) contribution into the Rhône downstream (station 4) during summer when other recharges are decreasing. While their contribution is only of 10-30 % during most of the year, those rivers could contribute to more than 60 % of the Rhône flow rate during the driest period. The current study aims at confirming the key role of Alpine rivers contribution to the Rhône downstream flow by investigating an alternative monitoring tool of high-altitude water contribution. As a suitable tracer of latitude and altitude especially in a contrasted morphology, such as the Rhône watershed, water stable isotopes can be relevant to trace the origin of the recharge contributing to the waterflow. This study is based on a full hydrological cycle survey of the Rhône downstream water isotopes signature complemented by the current flow rate monitoring program of the Alpine rivers. With a linear regression model between both parameters data, the current study evidences the relevance of using water isotope signature to trace the seasonal change of water's origin and evaluate the high altitude waters contribution (RQ AR) into the Rhône river downstream flow rate (δ 2 H ¼ 26.0 x RQ AR-57.9 with R ¼ 0.88, R 2 ¼ 0.79 and a p-value < 0.0001). It also confirms the key role of Alpine waters contribution to the Rhône River during summer with average value of 70 AE 6% and the importance to monitor the sustainability of their contribution in future drier period

Tracking natural and anthropogenic origins of dissolved arsenic during surface and groundwater interaction in a post-closure mining context: Isotopic constraints

International audienc

Origin of Salinity in a Coastal Karst System: La Clape Massif, SE France

International audienc

Water quality changes during aquifer storage and recovery at Bolivar, South Australia

International audienceThe use of reclaimed water in aquifer storage and recovery (ASR) is an important tool for water sustainability in arid regions. The demand on groundwater is reduced and abundant resources, such as storm water or sewage effluent, are utilised. A field trial at Bolivar, South Australia is investigating the viability of reclaimed water ASR in a limestone aquifer. Injection of 250 ML reclaimed water was followed by approximately 16 weeks of storage with subsequent recovery of 150 ML. Upon commencement of injection both aerobic organic matter oxidation and denitrification were observed within a 4m radius from the injection well. In contrast, the storage phase was indicative of higher microbial activity centred at the ASR well. Sulphate reduction up to 1.5 mmol L−1 was evident in water sampled from the ASR well while sulphate concentrations at the 4m radius remained constant. Buffering by dissolution of calcium carbonate was evident during both the injection and storage period

Innovative isotopic method to evaluate bioaccumulation of As and MTEs in Vitis vinifera

International audienceThe transfer of metal and metalloid trace elements (MTEs) from contaminated soil to grapevines is a major issue for grape consumption and for the associated health risks. Based on an isotopic approach, we shed light on the concept of MTE bioavailability. The bioavailable fractions are identified by using the Sr-isotope ratio as a proxy for MTEs. This allows us to differentiate three soil reservoirs: the ‘current available fraction’ in soil water, the ‘reserve available fraction’ stored in mineral phases of the soil fractions, and the ‘non-available fraction’. The reserve available fraction, representing 10 to 60% of bulk soil depending on the MTE, includes the exchangeable, carbonates, humic substance and oxides fractions. The 87Sr/86Sr isotopic signatures of grape berries and vine leaves show an additional source of MTEs, which is imported by foliar uptake and can contribute up to 10% of the MTEs in leaves. In addition, root-uptake and translocation rates show high accumulation rates of Co, Sn and Cu, and low ones for As, Sb, Zn and Cd. A daily intake between 1 and 3 kg of (dry grapes) would reach the benchmark dose level for a 0.5% (BMDL0.5). While such a daily intake of grapes is unreasonable, consumption of other local vegetables and fruit would contribute to the daily intake. Hence, a chronic arsenic exposure is of great concern for human health in mining areas. We outline the importance of geochemical tracers, such as Sr isotopes, when determining the transfer and translocation of MTEs in plants. Our method presents a high-precision evaluation of the bioavailability and bioaccumulation of MTEs, and a better understanding of these processes in plants, thus leading to a better assessment of the environmental risk on human health

Reconstructing natural groundwater flow and geochemical processes in a perturbed multi-layer aquifer system

Leide

Long-term impact of wastewater effluent discharge on groundwater: identification of contaminant plume by geochemical, isotopic, and organic tracers' approach

International audienc

Groundwater residence time and flow velocity in confined tertiary aquifers of the Northern Adelaide Plains, South Australia

Adelaide, S