Navegando por Autor "Augustin, Cristina Helena Ribeiro Rocha"
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Item Late Holocene in central Brazil : vegetation changes and humidity variability in a tropical wetland.(2021) Sabino, Shirley Maria Lima; Cassino, Raquel Franco; Gomes, Makênia Oliveira Soares; Sant'Anna, Eneida Maria Eskinazi; Augustin, Cristina Helena Ribeiro Rocha; Oliveira, Diego Alves deThe Pandeiros wetland is a high biodiversity ecosystem located within a semiarid region of the Cerrado biome, a neotropical savanna. This large wetland is of key importance for ecological and hydrological balance in central Brazil and for the conservation of the Cerrado fauna and flora. In this study, we present the first palaeoecological investigation of the Pandeiros wetland based on pollen analysis of a palm swamp sediment core encompassing the Late Holocene. Our results show that the wetland was subject to multicentennial‐scale oscillations in water availability during the Late Holocene; in particular, higher local humidity was documented between 4100 and 3100 cal a BP and from 2600 to 1000 cal a BP, and two events of drier local conditions occurred at approximately 2900 and 900 cal a BP. Our results also indicate a general decreasing trend in arboreal density in the Pandeiros River Basin from the beginning of the Late Holocene to the present, with the greatest expansion of dry forest occurring between 3600 and 3100 cal a BP.Item Millennial-scale variability of water supply, vegetation and fire activity on a tropical wetland in central Brazil.(2023) Cassino, Raquel Franco; Sabino, Shirley Maria Lima; Caixeta, Mariana Letícia; Oliveira, Diego Alves de; Gomes, Makênia Oliveira Soares; Sant’Anna, Eneida Maria Eskinazi; Augustin, Cristina Helena Ribeiro RochaThe Pandeiros wetland is a tropical wetland located in the ecotone between the Cerrado and the Caatinga, in central Brazil. It has a key ecological importance for vegetation biodiversity, hydrological cycles, fauna reproduction and feeding, and for local human populations. Here, we investigate millennial-scale variability of water supply, vegetation structure and fire activity in the Pandeiros wetland during the Late Holocene and discuss forcing mechanisms that affected flooding, vegetation cover and fire regime within this fragile ecosystem. Our study is based on the previously studied pollen record of the Pandeiros palm swamp and on new charcoal analyses of two sediment cores that cover the last 4500 cal years, and their comparison to modern pollen and to available paleoclimatic data. Our results show that both local rainfall at the Pandeiros River basin and southern rainfall at the upper Sao ̃ Francisco River were important in maintaining water supply for the Pandeiros wetland during the last millennia. Our data also suggest that during Late Holocene the arboreal cover declined in the Cerrado of the Pandeiros Basin, an opposite trend to that observed in the wetter Cerrado-Atlantic Forest ecotone. We propose that increasing summer insolation in Southern Hemisphere was an important factor in maintaining low arboreal cover and open savanna vegetation on the drier areas around the Pandeiros wetland. Regarding fire activity, we suggest that until around 2600 cal yr BP, climate conditions were the most important driver of fire activity, in which drier conditions favored the intensification of fire, whereas subsequently, anthropic activities appear to have become an important fire inducer. Our findings highlight the multiple environmental aspects that have influenced the Pandeiros wetland history during the last four thousand years, including monsoon variability, insolation variation and human occupation.Item The use of GPR for characterizing underground weathered profiles in the sub-humid tropics.(2002) Aranha, Paulo Roberto Antunes; Augustin, Cristina Helena Ribeiro Rocha; Sobreira, Frederico GarciaGround penetrating radar (GPR) has been used as a tool to access information about ground subsurface features. Such information is very important for different types of studies, varying from those related to archeological research to those studying geological elements of bedrock. More recently, however, GPR has been increasingly applied to environmental studies, especially for soil research. This paper presents the results of an application of GPR for the study of weathered profiles. GPR was used to discover the degree of trustworthiness of the information on the ground subsurface through the interpretation of the results of the radar sections as well as the data collected from boreholes, which reached until 21 m. The results show a relatively high degree of details obtained by GPR, indicating the possibility of speeding up ground subsurface surveys related to geomorphological, geological, and pedological studies.