ABSTRACT
One of the particularities of the unsaturated zone (UZ) is that it places in physical contact (i) the atmospheric air; (ii) a solution of variable composition (that depends on both depth and interaction time with the solid matrix), either percolating as free water or held in pores by capillarity; and (iii) minerals and organic matter. Geochemically, the coexistence of two types of water (percolating vs. capillary), each having its own spatial and time dynamics of interactions with solids, organics, and air is a basic characteristic of the soil systems.
