Stable states,buffers and switches: An ecosystem approach to the restoration and management of shallow lakes in The Netherlands

Lake restoration in the Netherlands has been focused mainly on the control of external P loading from point sources. However, this approach did not result in the water quality desired. The algae-dominated turbid water state may be extremely stable, and then additional measures are necessary to remove certain ‘blockages’ such as: the persistent bloom of Oscillatoria algae, the P release from the lake sediments, and the abundance of fish, preventing zooplankton and submerged macrophytes from developing . This paper addresses: (1) the need for an ecosystem approach, (2) the resistance of shallow lake ecosystems to changes in nutrient loading, (3) the concept of stable states, buffers and switches, and (4) the perspectives for lake restoration in the Netherlands. Priority should be given to fighting the Oscillatoria blooms. Winter flushing with water low in TP and algae proved to be an effective tool for reducing these blooms. Reduction of planktivorous fish, such as bream and roach, could enhance the top-down control of algae through the grazing by zooplankton, particularly by the large Daphnia species.