The relation is discussed between management, hydrology and the resulting vegetational succession during the period between 1975 and 1980 in a characteristic lower course of a Drenthian brook. The hay-making without fertilizer application could eventually lead to a gradient from Caricioncurto nigrae at the valley flank to Magnocaricion adjacent to the brook. These communities are related to mesotrophic mineral-rich groundwater seeping from a deep aquifer, groundwater with a short residence time in the soil with rainwater characteristics, and an intermediate groundwater type. The actual vegetational succession reveals an increase of the nutrient-rich communities of Glyceria maxima and Carex acuta/Carex aquatilis typicum and of the nutrient-poor community of Carex nigra, whereas mesotrophic Magnocaricion communities decreased. This is probably caused by a deep land consolidation ditch adjacent to the nature reserve diverting the base flow. Mineralrich groundwater, therefore, is replaced by mineral-poor rainwater on the one hand and by nutrientrich flood water on the other hand. Management practices inside a nature reserve can thus be seriously countered by qualitative hydrological changes outside a reserve even with slightly higher groundwater tables.