UNDERSTANDING A COMPLEX SYSTEM AQUIFER USINGGEOCHEMISTRY AND ISOTOPICCOMPOSITION (SIERRA DE GáDOR,SE SPAIN)

摘要

Sierra de Gádor aquifer system is currently exploited to irrigate some 20,000 ha of highly profitable early-seasonrngreenhouse crops. This area is named Campo de Dalías. A product of this proliferation of greenhouses is a flourishing local economy,rnfor which the volume of business approaches one billion dollars per year. In addition, they supply more than 200,000 people withrndrinking water and more than double this number during the summer months. The area is characterised by a wide variability inrnannual precipitation, indicative of the arid conditions. The geometry of the system is highly complex. This is compartmentalized by arnlarge number of fractures, which may even cause geothermal anomalies.rnThe theme of the present communication is a study of the principal hydrogeochemical and isotopic characteristics of the area,rnas well as a characterisation of the different types of freshwater, some of which are affected by the process of mixing with saltwater -rnparticularly those in the extreme east of the Sierra de Gádor-. Determining the content of O-18 and deuterium in the groundwater hasrnenable identification of the flow system of the waters, the recharge and mixing processes and the possible mechanisms of salinization.rnThe variation of O-18 content with altitude (-0.32 per mille per 100 m) enables an estimation of the principal recharge area. Nornseasonal variation in the isotopes was observed, which suggests that the residence time of the groundwater in the aquifer is severalrnyears. Radiocarbon dating gave estimates of generally long residence times, although in some sectors it is possible to detect therncurrent recharge based on its tritium content, from rainwater infiltration or seawater intrusion. In addition, the analysis of thernhydrogeochemistry of the groundwater enables a calculation of the principal geochemical reactions occurring in the aquifer.