Some impacts of urban waste landfills on Mediterranean soils

Seventy soil samples around and under urban waste landfills in central Spain were studied for 28 physical and chemical properties. In the unaffected surroundings of landfills there is always a higher proportion of coarse and fine gravel. Chlorides, sulphates and nitrates increase noticeably in all the soils affected by landfills as do Na⁺, B³⁺ and Zn²⁺. Multivariate analyses show that higher or lower water retention in the surface layer plays a main role in the organization of both acid and sandier soils as well as of basic soils and those with a higher proportion of silt and clay. Depending on the acidity or basicity, however, the other main factors reveal different hierarchical levels in the soil variables with regard to the organization of these systems. Thus, in acid soils, Zn²⁺ and B³⁺ contribute most noticeably to the second hierarchical level in the edaphic organization. In basic soil without gypsum, the second important gradient of variation is the stoniness (gravel)–fine sand (<2 mm fraction) while the importance of the K⁺, B³⁺ and SO₄⁼ is relegated to the third factor. In the basic soils with gypsum, not only sulphate, but also Na⁺, Cl⁻ and Zn²⁺ plays an essential role in the first factor and the coarse surface elements are also important. The principal components analysis made it possible to establish the main factors involved in the degradation caused by leachates from landfills. Consequently, greater attention could be given to these factors with a view to rehabilitation of degraded soils. © 1998 John Wiley & Sons, Ltd.