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 Niño 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 growth and reproduction. The recharge pattern can also influence the behavior of other functional groups characterized by a dimorphic root systems than can perform hydraulic redistribution. Part of the fast recharge of the aquifer could be related to this water redistribution. This study also shows that wetlands near the coast are fed mainly by groundwater associated with regional groundwater systems linked to recharge areas located in the high part of the Elqui River Basin. © 2006 Elsevier Ltd. All rights reserved.