Origen y funcionamiento hidrogeológico del único criptohumedal subhalófilo-alcalinófilo en la facies Guadalajara del acuífero Terciario detrítico de Madrid

Abstract

Dehesa de Arriba wetland is a subhalofite-alkalinofite reed meadow so far not described among the Madrid tertiary aquifer wetlands. Is located in the medium-high area of Henares river tertiary basin. The evaporation phenomena are the reason of its diversity and the presence of alkaline efflorescence. The water in origin is the discharge of small evolve groundwater, of the type HCO 3 -Ca and mineralization of 700 μS/cm, 2 km southward from the point where Camarmilla is captured by Torote river. The morphology of the wetland play an important role in the distribution of the species and the alkaline efflorescence since determine the phreatic level depth and affects the extent of capillary water up to the surface. The drainage of the soils in scarce because the smooth topography and the small erosion of the river after its capture. To the wetland, that is now the born of the Camarmilla stream, arrives 56.400 m 3 of groundwater annually and its soils generate a surplus of 29.000 m 3 from december to may in average years. The alkalinity is high in any area, although is higher in the graminoids and cyperaceous zones and is the highest in the efflorescence with a pH of 10.3 and a concentration of Na+ in its solution of 2871 mg/l. No significant difference of these parameters have been found between the soils where juncus acutus is located and other juncacea soils. The formation processes of this wetland and its high plants diversity make it singular in the Madrid aquifer context and constitute a unique enclave in Castilla-La Mancha.