Water level fluctuations in rich fens: an assessment of ecological benefits and drawbacks

For the proper functioning of endangered biodiverse rich fens, base-rich and nutrient-poor (mesotrophic) conditions are required to prevent succession towards Sphagnum-dominated peatlands. Unfortunately, water- and soil quality of many European wetlands are negatively affected by changes in hydrology, eutrophication, acidification and toxicity, resulting in a decline in brown moss-dominated, biodiverse rich fens. During the past decades, water levels in European rich fen areas have often become constricted within narrow limits as a result of adjacent agricultural water management. From a management perspective, the re-establishment of fluctuating water levels in non-pristine fens is considered, in order to optimize the generic ecological quality and to conserve and restore the vegetation in current brown moss-dominated rich fens. This thesis provides an assessment of ecological benefits and drawbacks.
Area-specific chemical properties of peat soils and surface water, as determined by the geohydrological setting in the landscape, turned out to strongly determine the responses to surface water level-induced water table fluctuations in the peat soil. Especially the Ca- and Fe-contents of peat soils proved to be very important factors. In addition, the timing of temporary drought or inundation in the growing season turned out to be important, because of the strong interaction between biogeochemical processes and vegetation development. These findings not only contribute to the general biogeochemical and ecological understanding of water level-induced processes in rich fens, but are also valuable to support water and nature management authorities in decision-making.