Smectite in mangrove soils of the State of São Paulo, Brazil

Abstract

Smectitic clay minerals are frequently identified in mangrove soils, but there is little information about their types and origins. Besides their importance in the agronomical and geotechnical areas, smectites play an important environmental role by adsorbing nutrients, organic pollutants and heavy metals. Smectites found in mangrove soils can be of marine or continental detrital origin, or of neoformation origin. Thus, the objective of this study was to identify the types of smectites present in the State of São Paulo mangrove soils (Brazil), and to relate them to their possible origins. Soil samples were taken in five mangroves along the State of Sao Paulo State coast line. The mineral composition of the clay fraction was identified by X-ray Diffractometry (XRD) applying the Greene-Kelly test and by Fourier transform infrared spectroscopy (FTIR). Highlighting the peaks in the 3,560 cm-1 band and in the region near 798 and 820 cm-1, there was a predominance of nontronite in the soil at the Sítio Grande River, Pai Matos Island, Caranguejo Island and Itapanhaú River mangroves, and possibly a lower concentration of ferric montmorillonite in the Escuro River mangrove. Since the continental sediments in these environments are very poor in smectite, the origin of these minerals in the mangrove soils studied is related to sedimentation left by past marine transgressions, to neoformation processes, or yet to a combination of both origins.

Ni cycling in mangrove sediments from New Caledonia

“…Fe-bearing phase in mangrove sediments, and it was proposed to be either newly formed or inherited from past marine transgressions (De Souza-Júnior et al, 2010;Noël et al, 2014). In line with these findings, the high proportion of Ni associated to montmorillonite evidenced by our EXAFS analysis suggests that neoformed smectites may have trapped a major fraction of Ni in the sediments beneath vegetated stand (38-69% of total Ni; Fig.…”

Oxidation of Ni-Rich Mangrove Sediments after Isolation from the Sea (Dumbea Bay, New Caledonia): Fe and Ni Behavior and Environmental Implications

“…Above 50 cm, Fe K-edge XAS data indicate that Fe is hosted by goethite, ferrihydrite, schwertmannite, and illite, as a proxy for smectite (Figure c; Table SI-6). The occurrence of Fe-bearing smectite has already been demonstrated in mangrove sediments of New Caledonia, and it is considered to result either from in situ formation or to have been inherited from past marine transgressions . Goethite is the most abundant Fe­(III)-species in lateritic regoliths developed upon ultramafic rocks in New Caledonia , and it is thought to have been directly inherited from the erosion of these lateritic regoliths. , In contrast, ferrihydrite and schwertmannite have not been reported in the lateritic regoliths of New Caledonia and these two mineral species are considered to result from in situ precipitation in the mangrove sediments studied.…”

The origin of gley colors in hydromorphic vertisols: the study case of the coastal plain of the Río de la Plata estuary

“…The iron incorporation on clay structures would be an authigenic process, as mentioned for saltmarsh environments (de Souza-Júnior et al 2010), where cyclic changes in the redox potential promote pyrite oxidation and the subsequent nontronite neoformation, in presence of Si, Mg and Al (Fernandez-Caliani et al 2004). Although pyrite was not detected, it is probable that it might had been present during the Holocene saltmarsh that gave origin to the parental material of these soils (Cavallotto 1995;Gómez Samus et al 2017a, 2020.…”