GROUNDWATER AND ITS FUNCTIONING AT THEDO?ANA RAMSAR SITE WETLANDS (SW SPAIN):ROLE OF ENVIRONMENTAL ISOTOPES TO DEFINETHE FLOW SYSTEM

摘要

Out of the largely fl uctuating surface water marshes, many of the environmentalcharacteristics of the Do?ana ecosystems depend on groundwater outflow andshallow watertable. Groundwater flow in the dominantly sandy Plio–Quaternaryaquifer is complex and is currently undergoing important changes due to groundwaterdevelopment. The use of environmental isotopes 18 O, 2 H, 3 H, 13 C, 14 C, 34 S, 39 Ar and 85 Krhas been very successful for defi ning recharge areas, flow patterns, transit times andthe conceptual flow model. The importance of vertical groundwater flow in unconfinedareas, as well as the behaviour of pre–Holocene confined water has been assessed. Thus,mixing patterns and chemical evolution can be explained. Lagoons are mostly aquiferdischarge areas in which water evapourates. Some of the solutes remain trapped inbottom sediments and some are flushed out in wet events. This pattern is being changeddue to the intensive aquifer development in some areas and negative ecological impactsare appearing.