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Long‐term effects of aquifer overdraft and recovery on groundwater quality in a Ramsar wetland: Las Tablas de Daimiel National Park, Spain

Las Tablas de Daimiel National Park is one of Spain's most representative groundwater‐dependent ecosystems. Under natural conditions, water inflows combined brackish surface water from River Gigüela with freshwater inputs from River Guadiana and the underlying aquifer. Since the mid‐1970s, aquifer overexploitation caused the desiccation of the wetlands and neighbouring springs. The National Park remained in precarious hydrological conditions for three decades, with the only exception of rapid floods due to extreme rainfall events and sporadic water transfers from other basins. In the late 2000s, a decrease in groundwater abstraction and an extraordinarily wet period reversed the trend. The aquifer experienced an unexpected recovery of groundwater levels (over 20 m in some areas), thus restoring groundwater discharge to springs and wetlands. The complex historical evolution of the water balance in this site has resulted in substantial changes in surface and groundwater quality. This becomes evident when comparing the pre‐1980 groundwater quality and the hydrochemical status in the wetland in two different periods, under “dry” and “wet” conditions. Although the system is close to full recovery from the groundwater‐level viewpoint, bouncing back in the major hydrochemical constituents has not yet been obtained. These still appear to evolve in response to the previous overexploitation state. Moreover, in some sectors, there are groundwater‐dependent ecosystems that remain different to those found in preoverexploitation times. The experience of Las Tablas de Damiel provides an observatory of long‐term changes in wetland water quality, demonstrating that the effects of aquifer overexploitation on aquatic ecosystems are more than a mere alteration of the water balance and that groundwater quality is the key to aquifer and aquatic ecosystem sustainability.