Characterization of groundwater in the Souss upstream basin: Hydrochemical and environmental isotopes approaches

The hydrochemistry of major ions and environmental isotope compositions (18O, 2H) of water samples have been used to identify the chemical characteristics and the origin of groundwater in the Souss upstream basin. The total dissolved solids (TDS) did not exceed 1000 mg.L-1 with an average of 635 mg.L-1. Two chemical water types were observed: A calcium and magnesium bicarbonate type (Ca2+-Mg2+-HCO3-), forming the dominant water type generally observed in the plain along the Souss river and towards the piedmont of the Anti-Atlas Mountains; and a calcium sulphate type (Ca2+-SO42-), from the northwest of the study area, linked to the presence of phosphatic gypseous marls and limestone marls (Upper Cretaceous). The calculations of saturation indexes versus the main mineral phases have been carried out, using the PHREEQC program. The groundwater is saturated and slightly oversaturated with respect to carbonate minerals and under saturated with respect to evaporite minerals; surface waters show an oversaturation with respect to carbonate mineral phases, mainly dolomite. The groundwater composition is largely controlled by the dissolution of carbonate rocks known in this part of the basin. Stable isotope contents of groundwaters ranged from -7.96 to -6.26‰ for δ18O and from -49.47 to -39.28‰ for δD. The hydrogen (δD) and oxygen (δ18O) isotope signatures indicate a low evaporation of precipitations during infiltration and that the aquifer is highly influenced by the contribution of recharge water recharge from the High Atlas Mountains.Key words: Groundwater, hydrochemistry, stable isotopes, arid climate, Souss, Morocco

Détermination des modalités de recharge des aquifères par le biais des traceurs chimiques et isotopiques. Cas de la zone de contact Haut Atlas occidental – Plaine du Souss (SW du Maroc)

Determination of the origin of recharge of the unconfined aquifer in the right side of the Souss wadi between Agadir and Taroudant (South-western of Morocco) was based on the use of hydrochemical and isotopic analysis of groundwater, surface water and springs of the contact zone between the High-Atlas Chain and the Souss plain.The correspondence in the space evolution of the various chemical elements of evaporitic origin (SO42-, Cl-, Sr2+) in groundwater, piedmont springs, and surface water reveals the existence of recharge water from the adjacent High-Atlas Chain.The various recharge modes of the different aquifers (High Atlas and Souss plain) determined by isotopic analysis, shows that the source of groundwater for the unconfined Souss aquifer seems to be composite between a direct infiltration on the High-Atlas tributaries and a remote recharge from the bordering High Atlas aquifers.La determinación del origen de los aportes de agua de la capa freática de la ribera derecha del rio Souss entre Agadir y Taroudant (Suroeste de Marruecos) se ha basado en la hidroquímica y el análisis isotópico de las aguas subterráneas, aguas superficiales y manantiales de la zona de contacto entre el Alto Atlas y la llanura de Souss.La correspondencia en la evolución espacial de los diferentes elementos químicos de origen evaporítico (SO42-, Cl-, Sr2+) en las aguas subterráneas, manantiales de pie de monte y aguas superficiales, revela la existencia de una recarga de agua procedente de la cadena del Alto Atlas. El análisis de los modos de recarga de los diferentes acuíferos (Alto Atlas y llanura de Souss) determinado por análisis isotópico, demuestra que la alimentación de la capa freática de Souss a partir del Alto Atlas parece ser mixta, compuesta por una infiltración directa de los afluentes del Alto Atlas y una alimentación lejana desde los acuiferos que limitan con el borde del Alto Atlas

Capillary rise quantifications based on in-situ artificial deuterium peak displacement and laboratory soil characterization

International audienceIn arid environments, water rises from the saturated level of a shallow aquifer to the drying soil surface where evaporation occurs. This process plays important roles in terms of plant survival, salt balance and aquifer budget. A new field quantification method of this capillary rise flow is proposed using micro-injections (6 μL) of a deuteriumenriched solution (d value of 63 000‰ vs. V-SMOW) into unsaturated soil at a 1m depth. Evaluation of peak displacement from profile sampling 35 days later delivered an estimate that was compared with outputs of numerical simulation based on laboratory hydrodynamic measurements assuming a steady state regime. A rate of 3.7 cm y−1 was estimated at a Moroccan site, where the aquifer water depth was 2.44 m. This value was higher than that computed from the relationship between evaporation rates and water level depth based on natural isotopic profile estimates, but it was lower than every estimate established using integration of the van Genuchten closed-form functions for soil hydraulic conductivity and retention curv

Isotopic study and relationship between surface and groud waters under a semi-arid climate : case of Souss-Massa basin (South-west of Morocco)

International audienc

Isotopes and groundwater management strategies under semi-arid area: case of the Souss upstream basin (Morocco).

International audienceThis study concerns the Souss upstream basin. The objective is to investigate the characteristics of surface water and groundwater, to assess the impact of artificial recharge as reinforcement of the natural replenishment and assess the renewal of groundwater under semi-arid area. Two major water types are observed: (i) surface waters and upstream springs (least mineralized) and (ii) all groundwater samples (prevailing calcium and magnesium bicarbonate water type). Water isotopes show a low evaporation of precipitations during infiltration. Impoverishment in heavy isotopes is the characteristic of mountain rainfalls, or of a climate colder and wetter than present. Carbon-14 activities (34-94 pmc) indicate a long residence time. The artificial recharge is low compared to the reservoir volume, due to which the renewal rate is also low

Application of multiple isotopic and geochemical tracers for investigation of recharge, salinization, and residence time of water in the Souss–Massa aquifer, southwest of Morocco.

International audienc