Unravelling hydrological mechanisms behind fen deterioration in order to design restoration strategies

“Knowledge 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 palaeogroundwater
models at a high spatial and temporal resolution. These palaeo-models are representative
for five time slices of the time-frame 0 to 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-geo-hydrological 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 additional 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 lowproductive
fens. We discuss the consequences of these hydrological changes for the suitability and
availability of fen habitat sites.”

(Citaat: Loon, A. van – Unravelling hydrological mechanisms behind fen deterioration in order to design restoration strategies. PhD thesis Utrecht University)