Source of calcium for pedogenic CaCO3 formation in benchmark soils of a Mediterranean semiarid environment

Calcic and petrocalcic horizons (Bk and Bkm, respectively) commonly occur in soils of arid and semiarid regions. Studies carried out to investigate the source of calcium in CaCO3 formation have shown that dust and parent materials represent the main sources. The aim of this study was to investigate if gypsum may be a source of calcium for calcium carbonate formation and, eventually, to quantify it. Five soil pedons, developing on “Serie Gessoso- Solfifera”, were selected in a very representative forest Mediterranean ecosystem in Sicily (I). Pedons were opened, described in field and sampled according to the sequence of genetic horizons. Soil samples were analyzed to investigate 87/86Sr ratio in leached and residual soil fractions as well as total amount of carbonates and gypsum. Results allow us to assert that gypsum may be an important source of calcium for pedogenic CaCO3 formation in the investigated soils. The amount of calcium arising from gypsum change not only among the pedons but also among the horizons of the same pedon depending on its chemical and physical features.