Influence of the Ciguela River ditch on the wetland of Las Tablas de Daimiel National Park (Spain) in a period of drought

Las Tablas de Daimiel National Park (PNTD) is one of the most representative Mediterranean wetlands in the Iberian Peninsula. It developed under semiarid climate by concentrating both surface water and groundwater contributions from a major part of the Upper Guadiana basin. Under natural conditions, the wetland system was maintained by groundwater contributions. Nowadays, however, the Ciguela River ditch is an important element that channels different incoming waters into the Park such as extraordinary freshets, water diversions from the Tajo-Segura aqueduct, effluents from the sewage treatment plant of the town of Villarrubia de los Ojos and drainages from the superficial formations crossed along the ditch. Under current conditions, during drought periods, groundwater pumped from emergency wells and the Ciguela River ditch are the only sources of water inputs to the Park. In this context, chemical and isotopic composition of water in the Ciguela River ditch and its influence on the PNTD during a drought period are analysed. Results obtained show that the composition of water entering the Park through the ditch is determined by the biological, evaporative and mixing processes that take place along it. Treated sewage waters, which mainly contribute suspended solids and nutrients, mix with sulphate-rich waters drained from the superficial formations crossed along the ditch. So long as the Park is disconnected from the regional aquifer, it is evidenced that the composition of incoming waters through the Ciguela River ditch during drought periods is significantly different to the composition of groundwater discharges that used to maintain the wetland under natural regimen.