Modifications of the structural characteristics of new soil forming on industrial waste colonized by woody plants

A large industrial area on the dry land facing the Venice lagoon, in North East Italy, is currently being reclaimed. This paper focuses on the modifications of the structural characteristics occurring on the surface and along the profile of some industrial waste in an area that has been colonized by woody plants. Qualitative micromorphological observations of thin sections of undisturbed soil samples showed that all samples taken from the surface layer (0–5 cm) of the woody area looked similar to samples from natural forest soil abundant in organic matter and with an open and crumby structure rich in pores. In some samples the substrate alteration was still evident at a depth of 20–25 cm. Quantitative data on the soil pore system obtained by image analysis were consistent with previous findings and total porosity decreased along the profile from about 30% to less than 5%. Elongated pores were the most abundant in the majority of samples, and the intermediate size class (0.2–1.0 mm) was the most representative. Good structural properties were also confirmed by the cracking patterns of artificially dried surface soil samples, which showed a network of fine cracks. Comparisons are also given with an adjacent area where phytoextraction trials were carried out according to common agricultural practices.