Statistical evaluation of the relationships between spatial variability in the organic carbon content in gray forest soils, soil density, concentrations of heavy metals, and topography

The spatial variability in the organic carbon content (C_org) in the gray forest soils was studied in relation to topography, soil density (D); and concentrations of Al, Fe, K, Ca, Mg, Mn, Cu, and Zn measured at 47 points in the upper (0–10 cm) and lower (10–20 cm) layers by the X-ray fluorescent method. The study area (48 by 104 m) under meadow vegetation included the break of slope of a river valley with strongly eroded gray forest soils and active development of erosional processes. Methods of geomorphometry were used for the quantitative characterization of topographic conditions. Statistical relationships between the studied characteristics were investigated by multiple regression methods with verification of the models according to specially developed criteria. The obtained statistical relationships were used to develop 3D cartographic models of the C_org and D distribution in the two soil layers. It was shown that the content of C_org in the upper layer increased on south-facing slopes, whereas the content of C_org in the lower layer gained its maximum of southwestern slopes, and the reasons for this distribution were determined. The major characteristics of topography affecting the distribution of C_org in the different soil layers were identified. The C_org content in any soil layer was most tightly correlated with the D values; a less tight correlation was observed between the C_org and Mg contents. The Zn and Cu contents correlated with the C_org in the lower (10–20 cm) layer, whereas the Ca and Fe contents correlated with the C_org in the upper (0–10 cm) layer. The interpretation of the observed regularities involved data on the stability of metal complexes with humic acids under different conditions of the soil acidity; the effect of the erosional processes was also taken into account.