The groundwater-surface water interaction in wetland restoration management in the Netherlands

A century ago more than half of the Netherlands consisted of wetlands, including the Pleistocene cover sand areas that are elevated well above sea level. Most of the former wetlands have been cultivated, whereas the remaining wetlands suffer from acidification, eutrophication and a decline of groundwater or surface water levels. Sustainable wetland restoration is now one of the primary targets in the governmental policy regarding these valuable ecological reserves. The restoration potential of wetlands is largely limited by their geographical situation and the governing hydrological system(s). Sustainable restoration requires in-depth knowledge of the hydrological systems of the different wetland types. All aspects of the hydrological system need to be known including surface water, groundwater, stream sediments, stream banks, technical infrastructure and related physical, chemical and biological features and processes. In the present study, the influence of the water system was unraveled for the major Dutch freshwater wetland types on the basis of field-scale projects and with the help of modelling. In the Netherlands, where different types of land use are closely packed together, structural changes in agriculture and water supply are needed to achieve the restoration targets. However, even structural changes in agriculture will hardly be able to decrease the nutrient load to the level required for oligotrophic wetland systems. Restoration of the groundwater regime (both levels and discharge) to its former natural situation is often impossible. Wetland restoration can only be successful if a new balance in these conditions can be found.