HYDROLOGICAL CYCLE AND INTERANNUAL VARIABILITY OF THE AQUATIC COMMUNITY IN A TEMPORARY SALINE LAKE (FUENTE DE PIEDRA, SOUTHERN SPAIN)

Fuente de Piedra is a shallow, temporary saline lake whose seasonal be havior is strongly dependent on the annual hydrological budget. In thi s study, we outline the characteristics of Fuente de Piedra Lake for t wo years that had different hydrological budgets. The high precipitati ons in 1989-90 caused the lake not to dry as usual, and decreased both salinity and the amplitude of changes. There were also differences in nutrient dynamics, with generally lower concentrations of soluble rea ctive phosphorus and ammonium, whereas in the more humid year nitrate showed a distinct maximum in winter. Winter bloom chlorophyil a concen trations were also much higher in 1989-90 (>600 mu g 1(-1)) but there was also a winter productive phase that was presumably poorly coupled with consumption processes that predominate in spring. Planktonic asse mblages were different between years. Highly halotolerant phytoplankto n species (Dunaliella salina and D. viridis) became scarcer, and espec ially two previously unrecorded diatoms (Cyclotella sp. and Chaetocero s sp.) became dominant in the bloom time in the wet year. The species richness of the zooplankton increased in the wet year, with new specie s appearing that were not collected during 1987-88 (Branchinectella me dia, Daphnia mediterranea, Macrothrix sp., Arctodiaptomus salinus, Cyc lops sp., Sigara sp...). There was also a much higher development of m acrophytes (Ruppia drepanensis, Althenia orientalis, Lamprothamnium pa pulosum) and bird populations, especially flamingoes (Phoenicopterus r uber). Important interannual variations in this sort of system point t o the need for long term studies to observe the whole range of states that define the lake as an entity.