Eutrophication control in the Netherlands

Abstract

Due to the limited perspectives of the Dutch national policy and due to the unique conditions and constraints of individual lake systems, tailor-made programs are needed for the restoration of freshwater lakes. Based on an evaluation of several restoration projects, a guideline is provided to enable water managers to develop such a restoration program. This guide-line is summarized in the paper and important topics, such as the definition of targets and standards, system identification and measures, are highlighted. Targets should include a natural reference, but also the constraints imposed by other functions of the lake. Monitoring and system identification are necessary to determine the extent of remedial measures and whether they should focus on external nutrient sources, internal sources or other factors, such as the food web structure. It is advocated that for lakes which have not degraded to a green, algal-dominated, turbid state, prevention or re-establishment of its ability to self-restore are preferred to ‘intensive surgery’ on the system. Lake re-creation can be applied if the system is heavily perturbed. In that case the re-creation of a more beneficial system is a more fair-minded approach than restoration of the natural state.