Concentrations of rare-earth elements in soils of the Prioksko-Terrasnyi state biospheric reserve

The concentrations of rare-earth elements were studied in the profiles of soddy podburs and mucky-humus gley soils. The soil horizons differed significantly in the contents of Corg (0–26%), the physical clay (<0.01 mm) fraction (3–31%), the acidity (pH 4 to 5.5), and the presence/absence of Al-Fe-humus accumulations. The most significant relationship was observed between the concentrations of rare-earth elements and the physical clay content, particularly for Nd: x(Nd, mg/kg) = 7 + 1.6y (fraction <0.01 mm, %). Weak biogenic accumulations in the upper horizons were observed for Nd, Ce, and Dy; Nd, Pr, and La accumulated in the Al-Fe-humus illuvial horizon. The concentrations of rare-earth elements in the studied soils formed the following sequence (mg/kg): Nd (20–101)-Ce (10–44)-La, Sm, Gd, Dy, Yb (3–20)-Pr (1–4)-Ho (0.1–0.4)-Tm, Lu, and Tl (0.0). A clear trend was observed to higher contents of even-numbered elements as compared with odd-numbered elements, excluding La.