Boy Possen, Bas van der Weijden, Jerry van Dijk, Hans de Mars, Martin Wassen & Tom van den Broek

Vernatting, herstelprojecten, biogeochemie, hydrologie, nutriëntenlimitatie

Matig voedselrijke natte graslanden, zoals het zeldzame blauwgrasland, hebben sterk te lijden onder verdroging. Het simpelweg opzetten van het grond- of oppervlaktewaterpeil, al dan niet in combinatie met ontgronden, leidt in veel gevallen echter niet tot herstel. Waarom is het resultaat van vernattingsprojecten nog steeds onvoorspelbaar, ondanks decennialang onderzoek? In dit artikel beantwoorden we die vraag en geven we sleutels voor succes, naast een aantal andere inzichten.

Summary: Rewetting, restoration projects, biogeochemistry, hydrology, nutrient limitation
Despite a long research tradition, results of rewetting projects are often not as expected. To help enhance predictability we used a ‘systematic literature review’ to compile an overview of current knowledge, focussing on wet grasslands. There is extensive knowledge on the role of iron, calcium, sulphur, phosphorus, pH, redox potential, their interactions and the decisive importance of hydrological conditions in determining vegetation development through nutrient availability or limitation. Two key factors determining the outcome of rewetting projects emerged: the hydrological system and growth limitation. Furthermore, a shift in focus towards site characteristics and away from the hydrological system the site is embedded in became apparent, while both co-determined conditions at a given site. This makes extrapolation of results beyond individual sites difficult and implies measures at both levels should be considered when assessing possibilities for rewetting. Also, it is important to recognise that conditions under which our reference for high quality wet grasslands developed were to a large extent created by historical land use practices. A successful rewetting project thus starts with the recognition that each site has its own unique characteristics co-determined by the hydrological system, which have to be understood in conjunction to increase predictability of rewetting projects.

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