Recharge sources and hydrogeological effects of irrigation and an influent river identified by stable isotopes in the Motril‐Salobreña aquifer (Southern Spain)

Abstract

Abstract:Measurement of the stable isotopes oxygen-18 and deuterium in water is an important tool to characterize aquifer recharge sources. In the driest areas of the Mediterranean, this application is of special interest due to the scarcity of water and the resulting common incidence of human influence on natural hydrological systems. The Motril-Salobreña detrital aquifer (southern Spain) is a clear example of such an impact as inhabitants have designed irrigation systems and a dam was recently built across the course of the Guadalfeo River, which feeds the aquifer. The sampling of (river or ground) water has allowed the determination of stable isotope contents (oxygen-18 and deuterium), both temporally and spatially, and the relative importance of the main recharge sources in certain sectors. In addition, we were able to infer seasonal trends and to improve existing knowledge of the main flow paths and the position of a seasonal groundwater divide. Data analysis shows evaporation plays a minor role (despite the high temperatures in the zone), scarce rainwater influence, and the overwhelming contribution of recharge from the Guadalfeo River and from the carbonate aquifer (Escalate aquifer) in contact with the Motril-Salobreña aquifer. Irrigation return flow during the summer months comprises the main recharge due to the significant volumes of water that infiltrate. The construction of the dam will almost certainly entail great changes in the current dynamics of the hydrogeology of the Motril-Salobreña aquifer; therefore, knowledge of its behaviour is crucial in order to carry out sustainable use of its groundwater resources.

Global Isotope Hydrogeology―Review

“…Differences between groundwater and precipitation δ 18 O or δ 2 H values can arise from many different processes, one being recharge from lakes, rivers, and diverted waters (Figures and ; e.g., Vogel, Lerman, & Mook, ; Vogel, Lerman, Mook & Roberts, ). Surface waters that have partially evaporated or derive from precipitation distal to the study area often have identifiable “end‐member” δ 18 O and δ 2 H values that can help distinguish these surface‐water recharge sources (Figures e and f; e.g., Christodoulou et al, ; Kass et al, ; Palmer et al, ; Duque et al, ; Vanderzalm et al, ). Specifically, examining the relationship among local groundwaters and the LMWL can frequently help identify groundwater supplied by surface waters with δ 18 O‐δ 2 H paired values indicative of evaporation (e.g., low deuterium excess values).…”

Application of Stable Isotopes of Water to Study Coupled Submarine Groundwater Discharge and Nutrient Delivery

“…Using stable isotopes of water as a tracer is a well-established discipline in hydrogeological studies that allows the differentiation of water exposed to different physical processes relating to precipitation and evaporation [27]. Its use has been applied with multiple objectives [28]: To quantify recharge sources [29][30][31], for climate assessment [32], or to evaluate water origin in lakes [33] or hydrothermal systems [34,35]. The continuous improvement in analytical techniques has enabled researchers to quantify 18 O and 2 H with small volumes of water through a simple and direct sampling system.…”

Groundwater-Surface Water Interactions in “La Charca de Suárez” Wetlands, Spain

“…The direction of groundwater flow is north-south with a hydraulic gradient estimated between 1.6 × 10 −3 and 5 × 10 −3 [33]. The main natural recharge of the aquifer is produced by infiltration from Guadalfeo River [29,34] and by irrigation return flows [29,34], estimated at 11 Mm 3 /year and 16 Mm 3 /year, respectively. Other minor contributions are produced by lateral inlets from the Escalate aquifer (4 Mm 3 /year) and rainfall recharge (3-6 Mm 3 /year) [29] and by the alluvium from the river (1 Mm 3 /year) [35].…”