Marcia Regina Calegari

Relationship between soil oxidizable carbon and physical, chemical and mineralogical properties of umbric ferralsols

SUMMARY The occurrence of Umbric Ferralsols with thick umbric epipedons (≥ ≥ ≥ ≥ 100 cm thickness) in humid Tropical and Subtropical areas is a paradox since the processes of organic matter decomposition in these environments are very efficient. Nevertheless, this soil type has been reported in areas in the Southeast and South of Brazil, and at some places in the Northeast. Aspects of the genesis and paleoenvironmental significance of these Ferralsols still need a better understanding. The processes that made the umbric horizons so thick and dark and contributed to the preservation of organic carbon (OC) at considerable depths in these soils are of special interest. In this study, eight Ferralsols with a thick umbric horizon (UF) under different vegetation types were sampled (tropical rain forest, tropical seasonal forest and savanna woodland) and their macromorphological, physical, chemical and mineralogical properties studied to detect soil characteristics that could explain the preservation of high carbon amounts at considerable depths. The studied UF are clayey to very clayey, strongly acidic, dystrophic, and Al-saturated and charcoal fragments are often scattered in the soil matrix. Kaolinites are the main clay minerals in the A and B horizons, followed by abundant gibbsite and hydroxyl-interlayered vermiculite. The latter was only found in UFs derived from basalt rock in the South of the country. Total carbon (TC) ranged from 5 to 101 g kg -1 in the umbric epipedon. Dichromateoxidizable organic carbon represented nearly 75 % of TC in the thick A horizons, while non-oxidizable C, which includes recalcitrant C (e.g., charcoal), contributed

EVOLUÇÃO DE BACIAS DE BAIXA ORDEM NOS 41.000 ANOS AP - BRASIL MERIDIONAL

Apresenta-se evolucao de bacias de baixa ordem hierarquica no Planalto de Palmas/Agua Doce (sul do Brasil) nos 41.000 anos AP a partir de registros de secao estratigrafica. Descreveu-se unidades litologicas e pedologicas, analise micromorfologica e datacao pelo 14C. Identificaram-se unidades litologicas facies aluvial, coluvio-aluvial, coluvial e tecnogenica; e duas unidades pedologicas (Neossolos). Conclui-se que no final do Pleistoceno Superior, sobretudo nos EIM 3 e 2, o sistema fluvial de baixa ordem hierarquica e o ambiente de encosta se encontravam em equilibrio dinâmico, registrando apenas um pulso de morfogenese. Nesse periodo o fundo de vale apresentou agradacao e desenvolvimento de Neossolo fluvico, em fase com paleossolos similares nas proximidades, atestando estabilidade morfogenetica de cunho regional. Na passagem para o Holoceno ocorreu intensa morfogenese das encostas e colmatacao dos fundos de vale das bacias de baixa ordem, perdurando ate cerca de 1.000 anos AP. Coincidindo com esta fase o divisor de aguas regional migra para Norte, com desmantelamento das bacias de 1a ordem do rio Chapecozinho (PR), rehierarquizacao da rede de drenagem e inversao de relevo.

Phytoliths as indicators of pedogenesis and paleoenvironmental changes in Spodosols of the state of Rio de Janeiro, Brazil

This study aims to contribute toward a better understanding of the current biodiversity patterns existing in the Atlantic Forest of the state of Rio de Janeiro from a paleo-ecological approach. Three soil profiles, each formed from distinct source materials under varied climate and vegetation conditions were selected from the coastal regions of Rio de Janeiro, Brazil. Soil horizon samples for chemical and physical characterization were collected from 10 cm-interval depths, and the total organic carbon was determined in addition to performing isotype and phytolithic analyses. The phytolithic analysis associated with the isotopic techniques (δ13C) permitted the characterization of three stages of paleo-environmental evolution for the studied soils, presenting valid trends that indicate small variations within the phytosociological structure of the vegetation along a Spodosols line in the studied areas. These stages indicated that the phytolithic assemblage was formed from a vegetation profile containing more trees, adapted to conditions colder than the existing vegetation, although no environmental changes were detected using the isotopic data. The milder temperature conditions may have favored the pedogenetic processes of the spodic B horizon formation as well as the maintenance of the organic matter contained in the soil. This study serves as the first draft for the paleo-environmental association among the regions where the analyzed profiles are found.