GROUNDWATER IN SEMI-ARID MEDITERRANEAN AREAS: DESERTIFICATION, SOIL SALIN1ZATION AND ECOSYSTEMS

摘要

An investigation concerning groundwater quality and its relation with the soil salinization, desertification and associated ecosystems is being developed in Alentejo, a region of South Portugal affected by a semi-arid climate. The precipitation occurs mainly during the cold season, between October and March/April, and the hot season has a heavy deficit of water. The geology is based on sedimentary and volcano-sedimentary rocks affected by the Hercynian orogeny. The plants and trees are adapted to this environment, where specific species resist to these conditions, as the Quercus suber, the cork oak. Some saline waters are present in certain areas, mainly on the flat ones, and the natural vegetation is controlled by the groundwater composition. Ecosystems with plants like Juncus acutus, Juncus subulatus, Hordeum geniculatum and Parapholis incurva are present and the human settlements tend to avoid those areas, where also the agriculture is difficult to implement. The presence of this type of waters is justified by deep faults that can transmit highly mineralized waters from deepness and by the concentration of salts at surface caused by the high values of evapotranspiration.