Journal of Arid Environments Journal of Arid Environments 67 (2006) 240–254 Groundwater dynamics in a coastal aquifer in north-central Chile: Implications for groundwater recharge in an arid ecosystem Francisco A. Squeo a,Ã , Ramon Aravena b , Evelyn Aguirre c , Alberto Pollastri c , Carmen B. Jorquera d , James R. Ehleringer e a Departamento de Biologı´a, Facultad de Ciencias, Universidad de La Serena, Centro de Estudios Avanzados en Zonas Aridas (CEAZA) and Institute of Ecology and Biodiversity (IEB), Casilla 599, La Serena, Chile b Department of Earth Sciences, University of Waterloo, Canada´ c Comisio´n Chilena de Energı´a Nuclear, Chile d Departamento de Agronomı´a, Facultad de Ciencias, Universidad de La Serena, Casilla 599, La Serena, Chile e Department of Biology, University of Utah, USA Received 5 January 2005; received in revised form 8 December 2005; accepted 23 February 2006 Available online 17 April 2006 Abstract The understanding of the water cycle is one of the key elements to evaluate the present and long- term primary productivity in arid ecosystems. This study uses hydrogeological and isotope tools to evaluate the recharge mechanisms in a coastal unconfined gravel and sand aquifer located in the arid zone of north-central Chile. The main water sources in the study area, fog, rain and groundwater, were isotopically characterized over a decade. The isotope data confirm previous studies based on fog capture, that fog does not play any role in groundwater recharge. The water table and isotope data showed that during low water conditions (dry periods), the aquifer is maintained primarily by water recharged in the higher part of the Romeral basin. During high water table conditions (wet periods), recharge associated with local precipitation becomes a significant source of groundwater recharge. The water table data showed that the aquifer responded very fast to rains with amounts over the average level for precipitation and the fastest response was observed during the El Nin˜ o year of 1997. No recharge was detected with precipitation events lower than the average value for precipitation. The aquifer recharge pattern in the coastal area of the Romeral Basin has significant implications for functional groups of plants characterized by deep root systems that have low capacity to respond directly to precipitation and consequently use groundwater as their main water source for new plant ARTICLE IN PRESS www.elsevier.com/locate/jnlabr/yjare 0140-1963/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jaridenv.2006.02.012 Ã Corresponding author. Tel.: +56 51 204369; fax: +56 51 204383. E-mail addresses: f_squeo@userena.cl (F.A. Squeo), roaraven@sciborg.uwaterloo.ca (R. Aravena), eaguirre@ cchen.cl (E. Aguirre), cjorque@userena.cl (C.B. Jorquera), ehleringer@biology.utah.edu (J.R. Ehleringer).