Dynamic modelling of forest vegetation functioning

• Modelling of forest vegetation functioning in relation to management of contaminated sites

Due to their perennial character, forest vegetation or perennial vegetation systems in general, may affect radionuclide dispersion and distribution. Perennial vegetation systems are a promising alternative for the valorisation of contaminated areas or for phytostabilisation purposes ( e.g. Chernobyl affected area, areas affected by U exploitation). At contaminated sites, the extent of radionuclide availability to perennial plants and the extent of element cycling within the ecosystem can have important implications for the dispersion of radioactivity as well as for the possible economic valorisation of the forest products.

Through extensive sampling campaigns in forest vegetation stands and associated soil compartments of the Chernobyl affected area and in forest developed in an U exploitation area we were able to quantify the transfer and cycling of radiopollutants (Cs, U, Ra) and associated nutrients and develop a conceptual model to make projections for the distribution of these elements in the ecosystem with time.

This work was taken further in a study of the cycling of radioelements in forest vegetation developed on red forest burial site in Chernobyl and the assessment of the contribution of vegetation to the dispersion of radionuclides. This work is done in collaboration with IRSN and Ukrainian partners.

• Modelling of forest vegetation functioning in relation to radioactive waste disposal

Radionuclides present in high level radioactive waste repositories will eventually migrate and reach the upper aquifers. An important factor is the groundwater-soil-vegetation interaction which is also highly sensitive to climate change. A realistic description and quantification of the processes influencing the behaviour of radionuclides at the biosphere-geosphere interface is important for actual terrestrial ecosystems in order to assess the effect of perennial ecosystems on the dispersion and redistribution of radionuclides in the biosphere in the long-term and its consequent effect on exposure of man and environment. The forest ecosystem is one of the ecosystems of interest, covering large areas in the Belgian Campine region and this under different hydrological conditions.

• An operational vegetation model for the Mol region and a deep disposal scenario

In this context we started with an R&D project with the objective to contribute to the acquisition of the data and model functions necessary for the implementation, calibration and verification of an operational vegetation model for the Mol region and a deep disposal scenario.

Two test sites were selected (Coniferous: pine, 2004 and Deciduous: oak: 2007) and an extensive sampling scheme was set up to be able to assess the hydrological functioning (water balance), biomass production and turnover and element cycling [stable isotopes (I, Cl, Se, Ni, starting with Cl) and nutrients].

A hydrological model was developed which allowed to assess the contribution of the groundwater table to the global water flux in the forest ecosystems.

The biomass and nutrient uptake and cycling model is being developed and verified.

The outcome will allow to make a long-term assessment of the influence of a forest vegetation system on the radionuclide dispersion and the contamination of the soil layer and the subsequent exposure to man and environment.

People: Olyslaegers Geert, Van Hees May, Catherine Van den Hoof