Chemical fate of iron in a peatland developing in the southern Espinhaço chain, Brazil

Abstract

A peatland (geographical coordinates of the sampling site, 18° 05′ 43.6″ S, 43° 47′ 6.4″ W; altitude 1,330 m asl) in São João da Chapada, municipality of Diamantina, state of Minas Gerais, was sampled at different depths of two profiles with different vegetation coverings (namely, field grassland and bush) in order to collect materials that might reflect changes of the chemical states of iron over the peat formation coming from original minerals like basic rock very likely influenced by hematitic phyllite surrounding the boggy pedon. Mössbauer spectroscopy spectra at room temperature and chemical composition analysis reveal that the iron contents for the peatlands under both vegetations decreases on going from the surface downwards. Also, a central doublet of (super)paramagnetic ferric chemical species, even for samples from deeper positions on the profile, where the reducing chemical potential of the pedoenvironment is thought to be higher, dominates the spectral patterns for all samples. In agreement with the Mössbauer results, magnetic measurements give evidence that the magnetic response of the surface samples is the highest, displaying a sharp decrease below 15 cm and a slight but steady increase with depth down along the profile.