Palaeo-hydrological reconstruction of a managed fen area in The Netherlands

SummaryKnowledge of the anthropogenic impact on the hydrology of low-productive fens that are subject to environmental degradation is essential to improve currently utilized hydrological fen restoration strategies. We analyse the naturally and anthropogenically driven evolution of groundwater systems in an intensively managed fen area in The Netherlands using a series of three-dimensional palaeo-groundwater models at a high spatial and temporal resolution. These palaeo-models are representative for five time slices of the time frame 0–2000 AD (Anno Domini), which are defined according to the timing of the natural and anthropogenic developments that had major impacts on the groundwater system configuration. For each time slice, palaeo-geohydrological conditions are reconstructed, which allowed for the calculation of groundwater discharge patterns, water balances and groundwater flow patterns.Contrary to former studies on the evolution of groundwater systems, our palaeo-hydrological reconstruction indicates that current groundwater discharge flux into managed fens may exceed the late-natural groundwater discharge flux. The increased groundwater discharge flux relates to the development of groundwater systems in the river valley with the establishment of polders since 1350 AD. Notably, more recent redirections of groundwater flow due to the reclamation of lakes and the establishment of abstractions wells, as well as the decreased groundwater recharge by anthropogenic land cover change, reduced the groundwater discharge flux only to a minor extent. This finding opposes the hypothesis that a decreased groundwater flux to fens underlies the environmental degradation of fens in intensively managed regions. The palaeo-hydrological reconstruction provides evidence that it is mainly the changes in the spatial configuration, and the shift in the predominant groundwater discharge mechanism, that underlies the environmental degradation of managed low-productive fens. We discuss the consequences of these hydrological changes for the suitability and availability of fen habitat sites.