Samenvatting

The Reeuwijkse Plassen have been dealing with a declining water quality for the past century. One of the problems is eutrophication due to in- and outflow of nutrient rich water from surrounding areas which caused algae blooms and turbid waters. The waterboard Hoogheemraadschap Rijnland implemented measures to improve the water quality according to Water Framework Directive (WFD). In 2011 two agricultural polders were disconnected from the Reeuwijkse Plassen to control in- and outflow of water and in 2012 construction of natural banks was started at all lakes. In 2014 and 2015 more polders were disconnected from the Reeuwijkse Plassen and a more naturally fluctuating water level was implemented. Because previous research showed that the Ecological Quality Ratio (EQR) score of the Reeuwijkse Plassen had not improved since the measures were taken, it was important to find out what has changed on a detailed level. This research thus looks into the changes in the species composition of macroinvertebrates at the Reeuwijkse Plassen after the WFD measures since 2010.