Histosol pedogenesis in floodplain coastal environments in the state of Rio de Janeiro, Brazil

Abstract

This study aimed to evaluate the morphological, physical, and chemical properties of Histosols in wetlands and to infer aspects related to their pedogenesis based on C and N isotopes and 14C dating to better understand ecosystem services, paleo-environments, and post-depositional processes based on preliminary results. Two Histosol pedons, located in different floodplains that refer to different sedimentation environments, were sampled in the state of Rio de Janeiro. Morphological, physical, and chemical characterization were performed, and the total C and N content of the substrate and the C content of humic substances were assessed. Elemental C and N and isotope analyses (δ13C and δ15N) were performed every 10 cm, while 14C dating of the humin fraction was performed at 40–50 and 190–200 cm. The interproxy approach combining pedological analyses, radiocarbon dating, and elemental and isotopic analyses of total C and N of organic matter, showed a mixture of algae and continental\ errestrial organic matter deposited in peatlands, over the last ~ 4000 cal years before present (BP). The studied soils were formed by geogenic and pedogenic processes (terrestrialization, paludization, and aggradation). Considering the relationships between δ13C and δ15N, between C/N and δ13C, and the soil characteristics, these deposits were probably formed by vertical accretion in lake environments. However, near 2300 cal yr BP, the radiocarbon dating and isotopic analyses suggest the occurrence of deposition of alluvial sediments transported by the Suruí River in RJ-01. It is likely that the modern age obtained by 14C dating in RJ-02, near 3600 cal yr BP, is probably due to the intense bioturbation by plant roots and the input of young material during the seasonal flood period.