Isotopic and Chemical Tracing for Residence Time and Recharge Mechanisms of Groundwater under Semi-Arid Climate: Case from Rif Mountains (Northern Morocco)

Abstract

Karstic aquifers play an important role for drinking and irrigation supply in Morocco. However, in some areas, a deeper understanding is needed in order to improve their sustainable management under global changes. Our study, based on chemical and isotopic investigation of 67 groundwater samples from the karst aquifer in the Rif Mountains, provides crucial information about the principal factors and processes influencing groundwater recharge and residence time. The δ18O and δ2H isotopic values indicate that the recharge is derived from meteoric water at high, intermediate, and low elevations for Lakraa Mountain, North of Lao River, and Haouz and Dersa Mountain aquifers, respectively. All samples show an isotopic signature from Atlantic Ocean except for those from the Lakraa Mountain aquifer, which shows Mediterranean Sea influence. Groundwater age determined by radiocarbon dating using the IAEA model indicates that the ages range from modern to 1460 years. This short residence time is consistent with the detectable tritium values (>2.7 TU) measured in groundwater. These values are similar to those of precipitation at the nearest GNIP stations of Gibraltar and Fez-Saiss, situated around 100 km north and 250 km south of the study area, respectively. This evidence indicates that groundwater in the Rif Mountains contains modern recharge (<60 years), testifying to significant renewability and the vulnerability of the hydrological system to climate variability and human activities. The results also indicate the efficiency of isotopic tracing in mountainous springs and would be helpful to decision makers for water in this karstic zone.

Multienvironmental tracers in coastal aquifer (Morocco): A window into groundwater mixing and risk to contamination

“…The absence of high 3 H activities in GW indicates that the 1960s 3 H peak in recharge has already decayed (Schlosser et al, 1988). This result is consistent with findings from other areas in Morocco, such as the Souss‐Massa, Tadla, and Rif regions (Bouchaou et al, 2008, 2009; Hssaisoune et al, 2022).…”

“…The findings of the current study are similar to those carried out in other parts of Morocco, particularly in coastal areas (Danni et al, 2019; Ez‐zaouy et al, 2022, 2023; Hssaisoune et al, 2017, 2022; Ouarani et al, 2021, 2023). The deterioration of GW quality is a major issue, which necessitates a sustainable and rationale use of this important resource.…”

“…In contrast, the deeper aquifer is most likely recharged in the Jbel Kourati and Jbel Hadid Mountains, where the elevations range from 242 to 800 masl, or during a wet period with a distinctly negative isotopic signature. These observations have been made in other regions of Morocco (Bouchaou et al, 2009;Ettayfi et al, 2012;Hssaisoune et al, 2019Hssaisoune et al, , 2022Khettouch et al, 2022;Qurtobi et al, 2010;Rhoujjati et al, 2021;Tijani et al, 2022;Warner et al, 2013).…”

“…Generally, the GW facies are determined by water–rock interaction, which is controlled by lithological type, and transit time (Ettayfi et al, 2012; Hssaisoune et al, 2022; Jamshidzadeh & Mirbagheri, 2011). The Piper (1944) diagram graphical method is used for determining the GW facies of the studied area.…”

“…The use of isotope tracers represents a valuable method for studying diverse hydrological concerns and assessing the hydrochemical and hydrogeological mechanisms governing any given GW system (Clark & Fritz, 1997). They supplement the evidence obtained from major ions by providing critical information about the water's source, recharge conditions (timing and location), direction of water flow, and residence time (Bouchaou et al, 2008(Bouchaou et al, , 2009Hssaisoune et al, 2019Hssaisoune et al, , 2022Khettouch et al, 2022).…”