Hydrological processes in a Cirsio-Molinietum fen meadow: Implications for restoration

Abstract

Cirsio-Molinietum fen meadows are seriously threatened by desiccation, acidification and eutrophication. In a nature reserve, with well-developed fen meadow stands groundwater tables and the chemical composition of groundwater and top soil were measured along a gradient during several years in the 1990s. The reserve consists of a depression, which is surrounded by ridges on all sides. Summer groundwater tables, which are being determined by regional features outside the reserve, drop down at least 1 m below the soil surface, whereas during the winter season a pool is formed. A concentrated flux of base-rich groundwater is brought up at the margin of the (eastern) exfiltration part of the pool, where downstream infiltration takes place. These processes, which cause a whole variety in site conditions, and consequently also in plant communities, are phenomena of a local groundwater system. An essential prerequisite for the functioning of such a groundwater system is the presence of pools during the winter season. When summer groundwater tables, which determine the origin and the extension of pools, are too low, measures outside nature reserves have to be taken to restore high summer water tables. Successful restoration of fen meadows requires sod cutting along the entire gradient. Since relatively small height differences can result in groundwater flow, restoring this type of hydrological systems on former agricultural areas requires first of all, restoration of the relief.