PHYSICOCHEMICAL CHARACTERISTICS OF A PERMANENT SPANISH HYPERSALINE LAKE - LA-SALADA-DE-CHIPRANA (NE SPAIN)

La Salada de Chiprana Lake, located in the Ebro River basin, northeast ern Spain, is the only permanent and deep water hypersaline ecosystem in all of western Europe. With a total surface of 31 ha and a maximum depth of 5.6 m, it has several basins bounded by elongated sandstone-b odies or ribbons which are paleochannels of Miocene age. Its salinity varied from 30 to 73 g l-1 during the 1989 hydrological cycle and the most abundant ions were magnesium and sulphate. Depth-time distributio ns of major physico-chemical variables demonstrated that the lake was stratified in two distinctive layers during most of the year. The chem ocline disappeared only in October, with the complete overturn of the water column. In the deep water, three conditions occurred which allow ed development of green sulphur bacteria populations: (1) oxygen deple tion, (2) presence of hydrogen sulphide and (3) presence of light. Ben thic microbial mats covered the sediments of shallow shores of moderat e slope.