
84 Małgorzata Pawłowska
composition can be used to prevent rapid drying of an open biofilter. Placement of the fine
grained material with a large water retention near the surface forms a barrier against drying
of the coarse material situated below, which is gas-permeable (Powelson et al. 2006). The use
of filter materials with a high content of organic matter is also the agent hedging them for
drying. The surface layer of the organic material becomes hydrophobic after drying. It leads
to the decrease of its capillary capacities, preventing transpiration from the surface (Huber-
Humer et al. 2008). What is more, the vegetation that could be placed ...