Groundwater salinity and hydrochemical processes in the volcano-sedimentary aquifer of La Aldea, Gran Canaria, Canary Islands, Spain Tatiana Cruz-Fuentes a, ⁎, María del Carmen Cabrera a , Javier Heredia b , Emilio Custodio c a Departamento de Física (GEOVOL), Universidad de Las Palmas de Gran Canaria, 35017 Las Palmas de Gran Canaria, Spain b Geological Institute of Spain (IGME), Ríos Rosas, 23, 28003 Madrid, Spain c Groundwater Hydrology Group, Department of Geo-Engineering, Technical University of Catalonia (UPC), Jordi Girona, 1-3, 08034 Barcelona, Spain HIGHLIGHTS • High groundwater salinity results from aridity. • Return irrigation flows are an important recharge source. • Groundwater reserves are essential in dry periods. • Groundwater quality is poor and needs mixing or desalination. • An exception to the European Water Framework Directive is needed. abstract article info Article history: Received 19 December 2013 Received in revised form 11 March 2014 Accepted 11 March 2014 Available online 1 April 2014 Editor: D. Barcelo Keywords: Hydrogeochemistry Salinization processes Return irrigation flows Modeling Volcanic–sedimentary aquifer Canary Islands The origin of the groundwater salinity and hydrochemical conditions of a 44 km 2 volcano-sedimentary aquifer in the semi-arid to arid La Aldea Valley (western Gran Canaria, Spain) has been studied, using major physical and chemical components. Current aquifer recharge is mainly the result of irrigation return flows and secondarily that of rainfall infiltration. Graphical, multivariate statistical and modeling tools have been applied in order to im- prove the hydrogeological conceptual model and identify the natural and anthropogenic factors controlling groundwater salinity. Groundwater ranges from Na–Cl–HCO 3 type for moderate salinity water to Na–Mg–Cl– SO 4 type for high salinity water. This is mainly the result of atmospheric airborne salt deposition; silicate weathering, and recharge incorporating irrigation return flows. High evapotranspiration produces significant evapo-concentration leading to relative high groundwater salinity in the area. Under average conditions, about 70% of the water used for intensive agricultural exploitation in the valley comes from three low salinity water runoff storage reservoirs upstream, out of the area, while the remaining 30% derives from groundwater. The main alluvial aquifer behaves as a short turnover time reservoir that adds to the surface waters to complement irrigation water supply in dry periods, when it reaches 70% of irrigation water requirements. The high seasonality and intra-annual variability of water demand for irrigation press on decision making on aquifer use by a large number of aquifer users acting on their own. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Salinization is a widespread groundwater natural contamination process in arid and semiarid coastal areas, but often it is also the result of human activities, such as agricultural practices. It occurs especially where the development of irrigated crop areas has caused intensive ex- ploitation of local groundwater resources. A number of papers dealing with groundwater salinization processes under arid and semi-arid con- ditions were published (Custodio, 1993; Herrera and Custodio, 2004; Jalali, 2007; Martos et al., 1999). Diverse mechanisms have been sug- gested to explain groundwater salinization in coastal areas: (1) seawa- ter intrusion (Custodio and Llamas, 1976; Custodio, 2010; Cruz et al., 2011), (2) evapo-concentration (concentration by evapotranspiration) of airborne salts (Alcalá and Custodio, 2008a; Guan et al., 2010), (3) hydrogeological characteristics of the aquifer (Ben Moussa et al., 2011; Farber et al., 2007), (4) water–rock interaction, such as dissolution, leaching and hydrolysis of minerals (Abid et al., 2011; Jalali, 2007; Van der Weijden and Pacheco, 2003) and (5) human influence, such as Science of the Total Environment 484 (2014) 154–166 ⁎ Corresponding author. Tel.: +34 928458080; fax: +34 928452922. E-mail addresses: tcruz@proyinves.ulpgc.es (T. Cruz-Fuentes), mcabrera@dfis.ulpgc.es (M.C. Cabrera), j.heredia@igme.es (J. Heredia), emilio.custodio@upc.edu (E. Custodio). http://dx.doi.org/10.1016/j.scitotenv.2014.03.041 0048-9697/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv