FIRST RESULTS OF THE RESTORATION OF LAKE GEERPLAS

In 1986 lake restoration was started in the Langeraar lakes, three sma ll connected lakes in the western part of The Netherlands. In one of t he lakes, Lake Geerplas, both the internal and external phosphorus loa d to the lake was reduced. Water quality parameters have been monitore d six years after the measures were taken, in both Lake Geerplas and i n one of the other Langeraar lakes. Water quality improved in Lake Gee rplas during four years, indicated by decreased phosphorus concentrati ons and turbidity. At the end of the third fourth summer, phosphorus c oncentrations increased rapidly, presumably due to excessive phosphoru s release from the lake sediment. Phytoplankton biomass and phytoplank ton composition changed as well. In the sixth year phosphorus concentr ations decreased slowly without any additional measures taken. Chlorop hyll-a concentrations and turbidity are at the same level now as short ly after the measures were taken. At this moment, the effects of the m easures are evaluated and additional measures are considered. Though t he changes in water quality variables during the years are clearly rel ated, the driving forces are not yet identified. (C) 1998 IAWQ. Publis hed by Elsevier Science Ltd.