Peat formation on a former landfill Production and decomposition of aquatic pioneer vegetation

The wetland Volgermeerpolder, the Netherlands, is newly constructed on top of a large dump site for household waste and chemical residues, and is expected to form peat layers as a sustainable barrier against dispersal of toxicants. This thesis aims to provide insight into the processes involved in organic matter build-up by colonising vegetation, using a conceptual model integrating biotic and abiotic drivers, accounting for ecological succession and interactions between environmental variables and the developing wetland communities. Water regime and sediment type were manipulated in a test area with 27 basins that allowed triplicate observations on vegetation development and biomass decomposition over a period of three years.
The containment of toxic waste in the Volgermeerpolder requires a replacement of the isolating geomembrane by a sufficiently thick cover of peat formed after 50 – 100 years. One decade after construction, the initial steps towards peat formation in the area are not unequivocally positive. Only the measurements in basins with the most productive helophyte stands potentially support expectations for rapid peat formation, with a potential to form an almost 20 cm thick layer of peat in a period of 50 years. However, a lower rate of formation may be expected given the risk for hampered peat growth by unsuitable water levels and concentrations of minerals in water. Only an optimised water management regime of the entire Volgermeerpolder combined with addition of nutrient-rich sediments to all basins allows the prospect of a peat layer growing quick enough to replace the degrading geomembrane in due time.