Restoration of Botshol (The Netherlands) by reduction of external load: Problem analyses and restoration methods

Abstract

Since 1960 the water quality of the nature reserve Botshol has been deteriorated. An increase in the nutrient load caused an escalation in phytoplankton biomass and turbidity problems. This may have been caused by nutrient-rich water flowing into the reserve from the agricultural areas and from the polder of Nellestein. From 1980 to 1985 much research has been undertaken and participation of different disciplines gave the opportunity to analyse the cause of the changes. An integrated restoration plan has been drawn up to reduce the eutrophication. The plan was implemented in 1989 and in order to reverse the external nutrient load the following measures were taken. 1. Execution of a water management plan with the intention to isolate the agricultural areas from the reserve area. 2. Dephosphorization of the inlet water. These restoration measures resulted in a reduction of the external load from 0.6 to 0.1 g P m−2 year−1.