Dependency of local mesotrophic fens on a regional groundwater flow system in a poldered river plain in the Netherlands

Abstract

The effect of regional, subregional and local groundwater flow systems on mesotrophic fen ecosystems was studied in the polders of the Vecht River plain that borders the Pleistocene ice-pushed moraine of Het Gooi. Variation in the vegetation and in the habitat factors (groundwater and peat soil) of fens depends whether or not the fens are connected to the outflow of the regional groundwater system. Changes in the regional groundwater flow system, caused by changes in the water management of the polders, are probably responsible for the deterioration of mesotrophic fens. Drastic measures will have to be taken to restore the hydrology on a regional scale if the mesotrophic fens are to be saved from extinction. Hydrological research that integrates the results of regional and local studies is essential if the ecology of fen ecosystems is to be understood.