Iron‐manganese Concretions in Hydrosequences of Soils in Loess in Bavaria

Abstract

Abstract To expand knowledge about the nature and distribution of Fe‐Mn concretions in soils, and in particular about their relation to degree of hydromorphism, the amounts and composition of concretions (0.2–0.63, 0.63–2.0, and >2.0‐mm diam) in profiles of two hydrosequences on loess in Bavaria, Germany were determined. Concretions were separated by wet sieving air‐dried soil samples. Maximum concretion formation (up to 7.5 weight percent) occurred in the upper B horizons (∼50‐cm depth) approaching the surface with increasing wetness. Maximum concretion formation (up to 40 kg/m 2 ) also occurred under medium wetness and not in the wettest profile. Mn, Fe, and P (except not P in the wettest members) were concentrated in the concretions, Fe predominantly as goethite, Mn presumably as birnessite and P (as concluded from correlations) adsorbed to Fe‐oxides, but not to Mn‐oxides. Selected concretion and microprobe studies showed that during concretion formation Mn with Some Fe is concentrated first with Mn being essentially exhausted at a later stage where nearly only Fe accumulates. Inasmuch as P from 2,000‐year‐old bones accumulated in concretions, their formation appears to have been continuing through recent time.