Hydro-geomorphologic controls in the vegetation of the Araguaia river floodplain, Brazil

A existência de diferentes tipologias vegetais na planície aluvial do médio Araguaia apresenta um padrão de distribuição determinado pela dinâmica fluvial do canal e pelas características morfossedimentares das unidades que formam a planície aluvial. O objetivo deste trabalho foi discutir como a dinâmica fluvial atua nos processos de sucessão vegetacional, considerando os processos de erosão e deposição, dentro de um curto intervalo temporal, e a dinâmica de cheias. O processamento de informações dos mapas das unidades morfossedimentares da planície e das unidades vegetacionais resultou no mapa de unidades morfovegetacionais. Verificou-se que as unidades vegetacionais se distribuem e compõem, de modo diversificado, um mosaico vegetacional pela planície. Entre 1965 e 1997, a ação dos processos erosivos, nas margens do canal que consomem a planície aluvial, tem removido principalmente vegetações arbóreas de grande porte, e as altas taxas de sedimentação contribuem para a formação da unidade geomorfológica mais jovem da planície, que é colonizada, sobretudo, por espécies herbáceas.The existence of different vegetable typologies in the alluvial plains of the middle Araguaia presents a pattern of distribution determined by the fluvial dynamic of the channel and the type of sediments that form different units of the alluvial plain. The purpose of this study was to discuss how the fluvial processes acts in vegetation succession, considering the erosive and sedimentary activities within a short period of time, as well as the flood dynamic. The combined information from morphosedimentary unit maps of the alluvial plain and the vegetation units allows the elaboration of the map of morphosedimentary units. It was possible to verify that the vegetation units were distributed in a diversified way along the alluvial plain, composing a vegetation mosaic. Between 1965 and 1997, the action of the erosive processes in the banks of the channel that consume the alluvial plain removed in particular large arboreal vegetation types, and the high rates of sedimentation contribute to the formation of the most recent geomorphologic unit of the plain, which is being colonized especially by herbaceous species.Facultad de Ciencias Naturales y Muse

Relationship between hydrology and aquatic ecosystems in the Araguaia river floodplain

O rio Araguaia se constitui no principal sistema fluvial que percorre o Brasil central. Neste artigo, são apresentadas algumas observações sobre o seu comportamento hidrogeomorfológico e suas aplicações no estudo de ecossistemas aquáticos. Os resultados foram gerados pelo processamento de dados de vazão de uma série histórica de 35 anos de registro (1970 a 2004), em nove estações hidrológicas, envolvendo o alto, médio e baixo curso. A distribuição de vazões no curso médio resulta atípica nas cheias extremas, pois o rio perde até 30% de sua vazão. No total, foram definidos três tipos de enchentes e dois mecanismos particulares de armazenamento e transferência de fluxos, que explicam as perdas de fluxos no médio curso. Três são os principais fatores condicionantes da perda de vazão: a) a existência de uma planície aluvial bem desenvolvida, b) a existência de um complexo de sistema de lagos na planície aluvial, c) a vegetação dominantemente arbórea, que freia a onda de cheia e contribui para o armazenamento de água na planície aluvial.The Araguaia river is the most important fluvial system draining the Cerrado biome of Brazil. Results are presented here on the hydrogeomorphologic behavior of this fluvial system and its effect on the floodplain ecosystems. Discharge from nine gauge stations in the upper, middle and lower course of the Araguaia River, from 1970 to 2004, were analyzed. The hydrological regime depends strongly on the tropical wet-dry climate, with floods from January to May and low water between June and September. In the upper and lower courses, there is a high variation between maximum and minimum peaks because the underdevelopment of the floodplain, while in the medium course the flow peaks are smoothed by the presence of a well-developed river floodplain. In this area, the river can lose up to 30% in water discharge, which is stored in the floodplain. Three types of flood categories were defined, and two mechanisms of flow storage and transfer were identified, explaining the discharge loss in the middle course. Three main mechanisms produce the water loss mid-course: the sponge effect of the alluvial plain, the existence of a well-developed mosaic of lakes, and an arboreal-dominated vegetation stratum of alluvial forest.Facultad de Ciencias Naturales y Muse

Author correction: One sixth of Amazonian tree diversity is dependent on river floodplains

In the version of the article initially published, the affiliation of Edgardo Manuel Latrubesse was incorrect and has now been amended to Environmental Sciences Graduate Program-CIAMB, Federal University of Goiás, Goiânia, Brazil in the HTML and PDF versions of the article

One sixth of Amazonian tree diversity is dependent on river floodplains

Amazonia’s floodplain system is the largest and most biodiverse on Earth. Although forests are crucial to the ecological integrity of floodplains, our understanding of their species composition and how this may differ from surrounding forest types is still far too limited, particularly as changing inundation regimes begin to reshape floodplain tree communities and the critical ecosystem functions they underpin. Here we address this gap by taking a spatially explicit look at Amazonia-wide patterns of tree-species turnover and ecological specialization of the region’s floodplain forests. We show that the majority of Amazonian tree species can inhabit floodplains, and about a sixth of Amazonian tree diversity is ecologically specialized on floodplains. The degree of specialization in floodplain communities is driven by regional flood patterns, with the most compositionally differentiated floodplain forests located centrally within the fluvial network and contingent on the most extraordinary flood magnitudes regionally. Our results provide a spatially explicit view of ecological specialization of floodplain forest communities and expose the need for whole-basin hydrological integrity to protect the Amazon’s tree diversity and its function

Patterns of anabranching channels: the ultimate end-member adjustment of mega rivers

Large fluvial systems adjust to a combination of controls to form distinctive channels, which represent a dominant factor in the evolution of floodplain geomorphology and sedimentology. Fluvial geomorphology has commonly classified river channels into meandering, straight and braiding patterns, which are seen to represent a continuum of channel geometry. Anabranching patterns, rivers with multiple channels, however, are characteristic of many rivers. The identification of a combination of variables that discriminates specific channel patterns has been a significant focus of research in fluvial geomorphology. The development of this body of knowledge, however, has been established from medium and small rivers, and laboratory flume studies. Very few of these research ideas developed from analysis of large fluvial systems. This paper assesses the pattern of channel adjustment of large fluvial systems by employing hydraulic geometry, discharge, w/d, slope, grain size, stream power, specific stream power, and Froude number (Qmean > 1000 m3/s). The study demonstrates that methods currently used to discriminate channel patterns are not useful when applied to very large rivers. Further, with the exception of the Lower Mississippi, alluvial rivers with mean annual discharges greater than ~ 17,000 m3/s, here classified as mega rivers, do not generate single thread meandering or typical braided patterns. These mega rivers develop anabranching patterns. © 2008 Elsevier B.V. All rights reserved.Fil: Latrubesse, Edgardo Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentin

RESENHA: ENTORNO NATURAL DE 17 CIDADES DA COLÔMBIA

Esta obra apareceu há quase dois anos, foi realizada por um amplo conjunto de especialistas (entre eles o coordenador) de reconhecido prestígio no âmbito internacional, e constitui um interessante modelo de como analisar a influência dos condicionantes naturais, principalmente os de tipo geológico, no assentamento e desenvolvimento das cidades. Dada a área geográfica que ocupa e o lugar de publicação, o livro teve uma difusão limitada fora da Colômbia, mas seu conteúdo possui um valor considerável para todos os interesados nos problemas relacionados com as interações entre as atividades humanas –especialmente os assentamentos urbanos e o meio geológico. Sendo, portanto, uma obra que centraliza-se em alguns dos temas definidos como de especial interesse dentro do Ano Internacional do Planeta Terra

A geomorphological assessment of wash-load sediment fluxes and floodplain sediment sinks along the lower Amazon River

We present the first spatiotemporal surface suspended sediment concentration (SSSC) analysis of the lower Amazon River, by combining geomorphological mapping, hydrosedimentological field investigations, and 15 years (2001–2015) of weekly averaged wash-load (fine sediment) fluxes at gauging stations estimated from field-calibrated remote-sensing models of SSSC. We found a downstream increase in the magnitude of sediment sinks, where the floodplain geomorphic style controls sediment trapping, and we conclude that the sediment net loss in the floodplain happens during the rising phase through seasonal hydrosedimentological connectivity. On average, 120 million tons per year of fine sediments are accumulated in the floodplain along 765 km of the lower Amazon River (from the confluence with the Madeira River to Monte Alegre city), making the lower Amazon River one of the most important fluvial sediment sinks among the world’s axial rivers.Published versio