Water-level Management as a Tool for the Restoration of Shallow Lakes in the Netherlands

ABSTRACT Water-level fluctuations are among the major driving forces for shallow lake ecosystems. In the low-lying parts of the Netherlands, the water-level regime of lakes is strictly regulated. This is needed for reducing risks of flooding and economic purposes, including maximum agricultural benefit. The fixation of water levels has had a severe impact on the functioning of (semi-)aquatic ecosystems. We review the benefits of natural water-level fluctuations, considering the impacts on nutrient inputs, nutrient concentrations, phytoplankton development and turbidity. In particular, the mediating role of submersed and emergent vegetation and filter feeders is addressed. The present government policy, to allow more space for water, presents a major challenge for combining flood prevention measures and ecological restoration. Restoration of natural water-level regimes, which is likely to lead to enhancement of water quality and biodiversity, may occur in two ways: (1) expanding the critical limits between which the water level is allowed to fluctuate annually, and/or (2) incidental recessions of the water level. It is stressed that ecologically-based water-level regimes should be incorporated into the context of multiple use of lakes.