PHOSPHORUS EVOLUTION IN 3 SUB-ALPINE LAKES - ANNECY, GENEVA AND LUGANO - INFLUENCE OF LAKE RESTORATION MANAGEMENTS

Concentrations of total phosphorus (TP) in three sub-alpine lakes (Lak e Annecy, Lake Lugano and Lake Geneva) between 1960 to 1990 are compar ed. For the three case studies, an increase of P concentrations was ob served in the mid 1960's. Later the P-evolution diverge due to the dif ferent remedial measures adopted. In Lake Annecy, restoration has been spectacular due to a complete diversion of all wastewater effluents. In the other lakes, reductions of P have been observed in the water co lumn after the peak concentrations in the late 1970's. Since this time , significant decline rates of TP have been noted ranging from -3 to - 5 mu g TP 1(-1) yr(-1). These improvements are clearly related to rest oration measures such as a partial sewage diversion for Lake Lugano or the ban on phosphates in detergents for Lake Geneva. One notable exce ption is deep hypolimnic waters of the northern basin of Lake Lugano, where the rate of P accumulation is about +3 mu g TP 1(-1) yr (-1).