Centre for Plant & Water Science - Central Queensland University

Centre for Plant & Water Science 2008 Annual Report
MODELLING THE ROLE OF VEGETATION IN PHYTOCAPPING
SUMMARY
Landfill has been the most popular method of disposing wastes in urban areas. Landfills mostly contain
putrescible wastes which can cause environmental hazards, if they come in contact with water. Thus,
preventing entry of water into buried waste is the most important aspect in landfill remediation. Currently
compacted clay capping is used to prevent percolation of water into waste. However, recent studies have
shown that this practice is often ineffective. An alternative capping system known as ‘Phytocapping’ was,
therefore, tested at Rockhampton. Phytocapping is the process of establishing vegetation on a layer of
soil placed over the waste, so that the soil layer stores the water during rainfall events and the plants will
remove the stored water during subsequent periods. Optimisation of these two events can result in
prevention of water entering the waste.
The Rockhampton trial involved the use of two depths of soil (thick 1400 mm and thin 700 mm) and 21
tree species. The trees and the soil were monitored for three years. The trial demonstrated that the
phytocapping can effectively limit the entry of water into the landfill, and the presence of vegetation is
critical to achieve a desirable site water balance. The predicted percolation was 133.3 mm yr -1 and 153
mm yr -1 in thick and thin systems respectively, when the vegetation component was removed in the
simulation, as compared to 16.7 mm yr -1 and 23.8 mm yr -1 when the vegetation component was included
in the simulation. Furthermore, the percolation rates in phytocapping systems (with vegetation) were
much less than those expected of a clay capping system. Since the phytocapping systems are effective,
they halve the cost of construction (compared to clay capping) and provide other environmental benefits,
their use is recommended in low (