The Deelense Was was part of an open heathland landscape until the start of this century. Starting in 2005, the number of trees surrounding it increased, leading to the current situation in which it is fully surrounded by trees, reaching all the way to the shores.
Stichting Bargerveen and Bosgroep Midden Nederland have, over the past period, conducted research into how the fen functions and the possible causes of its decline, commissioned by the Province of Gelderland. This research showed that the increase in the number of trees surrounding the fen is one of the causes. A restoration plan has been developed that focuses on improving the conditions needed for aquatic macrofauna, such as dragonfly larvae, to thrive.
Lack of oxygen
Oxygen stress is a major limiting factor for aquatic macroinvertebrates. During warm summers, oxygen concentrations periodically decline to critically low levels. This is because the decomposition of organic material in the sediment occurs rapidly under these conditions, consuming large amounts of oxygen. One of the main causes of the low oxygen concentrations is therefore the layer of sediment that has accumulated at the bottom of the pond. This sediment layer formed in the 1980s as a result of acid deposition, while over the past twenty years, leaf litter from the trees surrounding the pond has also contributed to further sediment accumulation. To reduce oxygen stress, the sediment layer will be removed. The vegetated banks will be preserved, ensuring that part of the current aquatic macroinvertebrate population remains and can contribute to recolonization.
Forest removal
To decrease the amount of leaves falling into the fen, most of the trees surrounding the Deelense Was will be removed. This will increase the impact of wind on the fen, which in turn will contribute to higher oxygen availability. This also prevents the northern and eastern shores from silting up again. Due to their ecological and landscape value, a few trees will remain.
Filling in the waterways
West of the Deelense Was lie two small ditches that no longer function. These ditches do influence the local groundwater level and with that, the potential for wet nature west of the fen. Due to this, the ditches will be filled in.
With these measures, De Hoge Veluwe National Park hopes to stop the decline of the Deelense Was and improve the fen, so that the Deelense Was will once again become a home for many species that thrive in an acidic fen.
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