Middle Amazon Research Articles

A Port by Any Other Name: A Preliminary Spatial Analysis of Ancient Infrastructural Landscapes and Settlement Organization at Macurany, Brazil

AbstractComplex human–environmental processes form identifiable, lasting features on the landscape that can illuminate past human behavior and human–environment interactions. We examine the anthropogenic landscape of the ancient port of Macurany, located along the middle Amazon River in Parintins, Brazil, and identify four classes of anthropogenic landscape features at the site: wharfs, middens, terra preta (dark or black earths), and cultural forests. Middens, terra preta, and cultural forests have been found at archaeological sites in regions surrounding Macurany, but wharfs have not previously been reported in Amazonian contexts predating European contact. Taken together, these features are clearly the result of anthropogenesis and represent a range of subsistence, settlement, and infrastructure-building activities pointing to an ancient society that was actively engaged in modifying the surrounding landscape for purposes beyond settlement and subsistence. Evidence for a permanent, extensive, continuously settled society practicing intensive landscape engineering in this region of Amazonia reinforces findings of dense habitation, infrastructure, and early urbanization in Amazonia prior to European contact. This research helps expand our understanding of human–environment interactions, landscape formation processes, and settlement organization in ancient Amazonia.

Relationships between fishery catch rates and land cover along a longitudinal gradient in floodplains of the Amazon River

Land cover is an important driver of patterns of fish diversity and assemblage structure in Amazonian floodplains. In the floodplain of the Amazon River, remarkable changes in the land cover composition across a longitudinal gradient, from the middle Amazon to the lower Amazon, likely affects fishery catch rates at local scales. Here, we investigated potential relationships between fishery catch rates and extent of land cover types in lakes of these two regions, the middle and lower floodplains of the Amazon River. Areas of flooded shrubs, herbaceous vegetation, and open water, within buffers of 1000 and 2000 m, were quantified around the areas of 23 lakes and modeled as predictors of fishing catch rate in the two subregions of the River i.e., the lower and middle Amazon, while these regions were also included as fixed effects of our models. Comparisons of the spatial extent of the land cover types between the two regions showed a predominance of flooded herbaceous vegetation in the downstream-lower portion, and a predominance of flooded shrubs and forests upstream-middle portion. In the models, the region was consistently the variable of greatest relative importance (Σwi > 0.9), and indicates higher fishing catch rate in the middle Amazon region when compared to the lower Amazon. Flooded shrub quantified on the smallest scale was the land cover type of strongest influence driving higher fishing catch rates, regardless of the region. In particular, our results support the idea that loss of flooded shrubs in adjacent areas of floodplain lakes can lead to reduced fishing catch rates at local and regional scales.

Impact of climate change in the flow regimes of the Upper and Middle Amazon River

Impact of climate change in the flow regimes of the Upper and Middle Amazon River

Ichthyofauna from tributaries of Urubu and Amazonas rivers, Amazonas State, Brazil

Abstract: The Amazonas River basin comprises the world’s highest fish species diversity. Anthropogenic interferences in aquatic environments represent a pressure over the maintenance of ecological stability and biodiversity. We inventoried the ichthyofauna of 13 disturbed/modified tributaries of Urubu and Amazonas rivers in the region of the middle Amazon River, between June 2018 and March 2019. A total of 164 species were captured, represented by 11 orders, 37 families and 96 genera. Characiformes was the richest order, followed by Cichliformes and Siluriformes. The most representative families in number of species were Cichlidae, Serrasalmidae, and Characidae. Hemigrammus levis was the most abundant species, and Acarichthys heckelii the most common, registered in all sampled sites. In the present study, species with economic interest were collected, as well as many species recently described and one still waiting for formal description, identified provisionally as Moenkhausia aff. colletii. Therefore, the high fish diversity registered, even in disturbed environments in Middle Amazonas River, denotes the makeable ecological importance of this region for fishes resources and supports the necessity of evaluation of other aquatic environments in the region, as well as the potential impacts on composition, maintenance, and survival of ichthyofauna in environments directly affected by human activities.

«O rio comanda a vida»: Aprendizagem do nado em uma comunidade ribeirinha do Amazonas

O objetivo deste artigo é descrever os processos e significados envolvidos na aprendizagem do nado entre crianças ribeirinhas do médio rio Solimões. A pesquisa questiona os métodos de aprendizagem e o que aprender a nadar representa em termos de construção da pessoa. Assim, recorremos a um estudo exploratório, com abordagem qualitativa e estudo de caso. Realizamos registros fotográficos, entrevistas semiestruturadas e observação participante. As crianças aprendem a nadar por meio de brincadeiras, em espaços específicos nas beiras dos rios, no período de inundação. Aprender a nadar lhes permite circular de forma autônoma nos espaços comunitários e lhes torna aptos a participar também do mundo da pesca. Concluímos que a natação é fundamental para a formação da pessoa, construção e afirmação da territorialidade do grupo.

GEOGRAFIA DAS COLÔNIAS AGRÍCOLAS NO MÉDIO RIO AMAZONAS, MUNICÍPIO DE URUCARÁ-AM/ Geography of agricultural colonies in the middle Amazon river, municipality of Urucará-AM

Os sujeitos sociais tratados nessa pesquisa foram os camponeses historicamente constituídos nas várzeas do médio rio Amazonas, em especial nos municípios de Urucará, Parintins e Urucurituba. Nesse ecossistema, pela absorção de diferentes traços culturais, estabeleceram relações econômicas, sociais e territoriais, condição que prevaleceu até meados da década de 1950, quando grandes enchentes/cheias e indisponibilidade de terras forçaram a migração permanente para as áreas de terra firme nas décadas de 1960/70. Historicamente a base de sustentação socioeconômica desses municípios, em especial Urucará, foco da nossa pesquisa, esteve ligada a atividade camponesa e suas possíveis relações com a terra, floresta e água possibilitaram uma agricultura de subsistência, práticas extrativas e atividades pesqueiras, destacando o protagonismo da várzea na vida e nas relações estabelecidas. Sua integração mercantil possibilitou trocas de produtos e mercadorias e ao mesmo tempo, relações de exploração e subordinação do trabalho camponês, sistema rompido ou acentuado pelas novas conjunturas políticas, econômicas e sociais da década de 1960. Essa década é emblemática não apenas pela visibilidade que os movimentos sociais no campo adquiriram no Brasil, mas especialmente pela organização e fortalecimento do campesinato no médio rio Amazonas. A territorialização camponesa na terra firme se deu através de Comunidades Eclesiais de Bases e colônias agrícolas, fortalecendo suas lutas através da criação de entidades (associações, cooperativas, sindicatos, Escola Família Agrícola) e principalmente, de uma instituição que coordenasse e articulasse as ações juntamente aos setores estatais, engajado de forma ou de outra, despertar a consciência política e social desses sujeitos sociais.

Geografia das colônias agrícolas no médio rio Amazonas, município de Urucará-AM

Os sujeitos sociais no qual tratamos nessa pesquisa, os colonos, camponeses historicamente constituídos nas várzeas do médio rio Amazonas, em especial nos municípios de Urucará, Parintins e Urucurituba. Nesse ecossistema, pela absorção de diferentes traços culturais, estabeleceram relações econômicas, sociais e territoriais, condição que prevaleceu até meados da década de 1950, quando grandes enchentes/cheias e indisponibilidade de terras forçaram a migração permanente para as áreas de terra firme nas décadas de 1960/70. Historicamente a base de sustentação socioeconômica desses municípios, em especial Urucará, foco da nossa pesquisa, esteve ligada a atividade camponesa e suas possíveis relações com a terra, floresta e água possibilitaram uma agricultura de subsistência, práticas extrativas e atividades pesqueiras, destacando o protagonismo da várzea na vida e nas relações estabelecidas. Sua integração mercantil possibilitou trocas de produtos e mercadorias e ao mesmo tempo, relações de exploração e subordinação do trabalho camponês, sistema rompido ou acentuado pelas novas conjunturas políticas, econômicas e sociais da década de 1960. Essa década é emblemática não apenas pela visibilidade que os movimentos sociais no campo adquiriram no Brasil, mas especialmente pela organização e fortalecimento do campesinato no médio rio Amazonas. A territorialização camponesa na terra firme se deu através de Comunidades Eclesiais de Bases e colônias agrícolas, fortalecendo suas lutas através da criação de entidades (associações, cooperativas, sindicatos, Escola Família Agrícola) e principalmente, de uma instituição que coordenasse e articulasse as ações juntamente aos setores estatais, engajado de forma ou de outra, a despertar a consciência política e social desses sujeitos sociais.

Distribuição de larvas de Brycon amazonicus (PISCES: BRYCONIDAE) no entorno da Reserva de Desenvolvimento Sustentável Mamirauá: base ecológica para manejo

A conservação dos recursos pesqueiros no médio Amazonas está relacionada ao conhecimento acerca dos seus estoques pesqueiros mais importantes, incluindo também o conhecimento sobre os padrões de recrutamento e desenvolvimento dos primeiros estágios de vida das espécies de maior importância econômica para a região. O presente trabalho amplia o conhecimento ecológico sobre a distribuição das larvas de Brycon amazonicus (matrinxã) a fim de verificar a importância dos ambientes fluviais para o recrutamento biológico dessa espécie, auxiliando no manejo sustentável e na conservação desse recurso pesqueiro da Amazônia Central. Este trabalho foi realizado no entorno da Reserva de Desenvolvimento Sustentável do Mamirauá (RDSM), e os dados obtidos foram provenientes de coletas diurnas e noturnas realizadas durante o período de enchente de 2011, no trecho médio do Rio Solimões e Baixo Rio Japurá, por meio de arrastos horizontais na superfície e em profundidade (8m), utilizando rede de plâncton 300µm em 16 estações de amostragem. Foram capturadas 310 larvas de matrinxã, sendo 148 indivíduos coletados no Rio Solimões e 162 no Rio Japurá. Observou-se que não houve um padrão claro de distribuição entre os habitats amostrados; entretanto, foi constatado variação da abundância larval indicando distribuição espacial (estratos da coluna d’água) e temporal (ciclo diário), com as maiores abundâncias registradas na subsuperfície da água durante o período noturno. Larvas registradas em estágios mais avançados de desenvolvimento refletem a importância da área de estudo para o recrutamento biológico, servindo como área de criação e alimentação para as larvas de matrinxã, sendo consideradas Habitats Essenciais para Peixes (EFHs) fundamentais para o manejo sustentável e conservação desse recurso pesqueiro da Amazônia Central.

Lateral variation of crustal properties from aerogeophysical data in northern Brazil

A new method is proposed for the study of crustal azimuthal anisotropy, and the lateral variation of other crustal aerogeophysical parameters, using a quantitative approach. The processing of a large, newly acquired, high-resolution set of aerogeophysical data is considered using the existing Radon transform and the geostatistical analysis approaches. The data set includes an area of the Guyana shield, in northern Brazil, which was not included in previous surveys. The area is covered by dense rain forest vegetation and thick soil layers. Parameterization was performed considering the possible anisotropic character of the geophysical 2D data. Application of the newly proposed geostatistical data processing yielded high-resolution images of the lateral variation of quantitative geophysical parameters, which indicate good correlation with previously determined seismic anisotropy in the area. Average anisotropy as measured by the Radon transform and variogram analysis is scale dependent. At scales greater than [Formula: see text], the results seem to match those of the previous seismic studies. Images of the derived quantitative parameters from magnetic and radiometric data in the shield area indicate sharp changes that follow the known geologic changes observable in the survey area. Observed large-scale anisotropy in the area seems to be autocorrelated with two different geochronological provinces of the Amazonian craton. Application of the new technique to two other lower resolution aeromagnetic surveys located on the Amazon basin has produced two different results, including one successful data treatment of the aeromagnetic survey. The results obtained for this area indicate that the sedimentary cover seems to play almost no role in the observed magnetic anomaly anisotropy in the middle Amazon basin area. Most of the observed magnetic anomalies appear to be controlled by the continuing geologic features of the cratonic basement.

Swiddens under transition: Consequences of agricultural intensification in the Amazon

Swidden cultivation is one of the most widespread agricultural systems in the tropics. Due to socio-economic changes, swiddens are either abandoned, substituted for other agricultural systems, or intensified. In the region of the middle Amazon river, Brazil, the high market demand for cassava flour (farinha) combined with land scarcity is inducing agricultural intensification. We define agricultural intensification as an increase in the frequency of swidden–fallow cycles and a decrease in the fallow period. In this study, we evaluate the consequences of agricultural intensification for management practices and swidden productivity in one of the main cassava producing areas of the Brazilian Amazon. We used ethnographic and biophysical surveys to characterize the current management practices and to evaluate the effect of repeated swidden–fallow cycles within a short fallow period regime on swidden size, weed infestation and life-form composition, weeding effort and cassava productivity. Our results show that with repeated swidden–fallow cycles cassava yield decreases, weed cover increases and weed composition changes from a tree-dominated to a graminoid-dominated community. Such changes in the weed community result in increased weeding effort, to which farmers respond by cultivating smaller swiddens. Therefore, the ongoing agricultural intensification leads to lower swidden productivity and household income without ensuing clear benefits for farmers. Limited access to fertilizers, herbicides and technical assistance combined with the market demand for a single product hinders adaptation. Broadening market opportunities and improving technical assistance to farmers could raise the diversification of production and sources of income and guarantee higher resilience to the system.

Revision of Tympanopleura Eigenmann (Siluriformes: Auchenipteridae) with description of two new species

The Neotropical catfish genus Tympanopleura, previously synonymized within Ageneiosus, is revalidated and included species are reviewed. Six species are recognized, two of which are described as new. Tympanopleura is distinguished from Ageneiosus by having an enlarged gas bladder not strongly encapsulated in bone; a prominent pseudotympanum consisting of an area on the side of the body devoid of epaxial musculature where the gas bladder contacts the internal coelomic wall; short, blunt head without greatly elongated jaws; and smaller adult body size. Species of Tympanopleura are distinguished from each other on the basis of unique meristic, morphometric, and pigmentation differences. Ageneiosus melanopogon and Tympanopleura nigricollis are junior synonyms of Tympanopleura atronasus. Tympanopleura alta is a junior synonym of Tympanopleura brevis. A lectotype is designated for T. brevis. Ageneiosus madeirensis is a junior synonym of Tympanopleura rondoni. Tympanopleura atronasus, T. brevis, T. longipinna, and T. rondoni are relatively widespread in the middle and upper Amazon River basin. Tympanopleura cryptica is described from relatively few specimens collected in the upper portion of the Amazon River basin in Peru and the middle portion of that basin in Brazil. Tympanopleura piperata is distributed in the upper and middle Amazon River basin, as well as in the Essequibo River drainage of Guyana.

A new species of Scinax Wagler, 1830 (Anura: Hylidae) from the middle Amazon river basin, Brazil

A new species of the hylid genus Scinax is described and illustrated. The new taxon was found in the Amazonian rainforest of northern Brazil, municipalities of Maués and Careiro da Várzea, state of Amazonas. The new species is characterized by its moderate size (male mean snout-vent length 36.3mm); body robust; large, orange, black-bordered axillary and inguinal spots; and bilobate vocal sac. This new species was found in primary and secondary forest on branches of shrubs or trees in, or next to, permanent ponds and flooded areas.

Caracterização e classificação de gleissolos da várzea do rio Solimões (Manacapuru e Iranduba), Amazonas, Brasil

As várzeas do rio Solimões são áreas inundáveis com predomínio de Gleissolos, onde se estabeleceu grande parte da população rural do Estado do Amazonas. Os objetivos deste trabalho foram caracterizar e classificar cinco perfis de Gleissolos, distribuídos em três áreas da bacia do Médio Amazonas, localizados nas várzeas dos municípios de Manacapuru e Iranduba. Após a descrição morfológica dos solos, coletaram-se amostras dos seus horizontes para caracterização física, química e mineralógica. Similarmente, todos os perfis apresentaram expressiva gleização na matriz do solo, com cores cinzenta a cinzenta-esverdeada, nos horizontes mais superficiais, e cinzenta-clara a cinzenta-escura, nos subsuperficiais, denotando a redução do ferro. Os teores mais elevados da fração areia em horizontes de subsuperfície indicaram presença de diferentes camadas de deposição fluvial, enquanto os elevados teores de silte evidenciaram a natureza sedimentar recente e o baixo grau de desenvolvimento pedogenético desses solos. Os cátions predominantes nos solos foram Ca2+ e Mg2+, que apresentaram porcentagens de sódio trocável (PST), com amplitude de variação entre 0,70 e 2,09. Os valores de carbono orgânico encontrados foram menores de 80 g kg-1, apresentando a natureza mineral dos sedimentos recém-depositados. A composição mineralógica da fração argila revelou presença significativa de argilominerais 2:1, mas sem grande variabilidade entre os perfis. Esses resultados refletiram-se em elevada soma e saturação por bases, caracterizando solos eutróficos e com argila de atividade alta.

The Early Stages of Speciation in Amazonian Forest Frogs: Phenotypic Conservatism Despite Strong Genetic Structure

Phylogeographic perspectives incorporating multiple classes of characters, especially those relating to sexual signals, are promising for the elucidation of recent evolutionary mechanisms driving speciation. Here, forest frogs were used as a model system to access distinct stages in the process of evolutionary differentiation. We studied 280 individuals assigned to three species: Allobates paleovarzensis, A. nidicola and A. masniger. Samples were collected at 20 localities arranged in two study systems, along the middle Amazon and the lower Madeira Rivers, in Central Amazonia. Mantel tests, analyses of molecular variance, and the spatial distribution of haplogroups indicated that the distribution of genetic variability, as inferred from a mitochondrial DNA marker, was determined by a combination of isolation-by-distance effects and the transposition of large Amazonian rivers. These two factors had contrasting relative influences in each of the study systems, which also differed regarding the estimated time of the major cladogenetic events. Pronounced population genetic structure was observed. However, multivariate discriminant function analyses revealed that the phenotypic (morphological and acoustic) divergence was loosely related with genetic differentiation and did not successfully predict assignment of individuals to genetic groups. The observed distribution of genetic variability showed the important role of genetic drift in the diversification of the mitochondrial marker studied. The phenotypic conservatism among populations was surprising in view of the high genetic structuring observed, and indicates a prevailing role of stabilizing selective forces in the process of sexual signal and morphological differentiation.

Floodplain channel morphology and networks of the middle Amazon River

Floodplain channels are important components of river‐floodplain systems and are known to play a key role in hydrodynamic exchange and sediment transport. The Amazon floodplain exhibits complex networks of these channels, and despite their potential importance to this globally important wetland system, these floodplain channels are relatively unstudied. The research presented here is the first systematic and detailed study of the network and morphologic characteristics of a large number of these channels in the middle reach of the central Amazon River using analysis of data derived from Landsat Enhanced Thematic Mapper Plus (ETM+) mosaic and field survey. Our findings show that the channels are ubiquitous, their width varies widely, and some of their characteristics can be fitted using power laws, potentially much like the self‐similar or fractal‐like behavior hypothesized for other types of fluvial networks. In all, 96% of the floodplain channels are not wide enough to be represented well, or at all, in the ∼90 m Shuttle Radar Topography Mission data. Channel depths are tied closely to the local amplitude of the passing main river flood wave (p value of 0.75), except where there are local runoff inputs, which results in substantially deeper channels which provide preferential flow paths across the floodplain. Channel networks imply that areas of the floodplain function for large parts of the flood cycle as separate hydrogeomorphic land units, here termed floodplain hydrological units (FHUs). These hypothesized FHUs also have distinct spatial and pattern characteristics, and it is suggested here that their differences could provide the beginnings of a framework for understanding the detailed hydrodynamics of the floodplain. In particular, different types of FHUs have differences in flood water source, which will have important implications for biogeochemical studies of the wetlands.

The anastomosing pattern and the extensively distributed scroll bars in the middle Amazon River

ABSTRACTThe middle Amazon River, between the confluences of the Negro and Madeira Rivers in Brazil, shows an anastomosing morphology with relatively stable, multiple interconnected channels that locally enclose floodbasins. Additionally, this system is characterized by sinuous secondary channels with meander development, discontinuous natural levees concentrated on the concave banks and extensively distributed scroll bars mainly in the islands, related to subrecent and present‐day migration of mainly secondary channels. This distinguishes the Amazon from many other anastomosing rivers that have laterally stable, non‐meandering channels. We analyzed sedimentary processes using field data, morphology and channel changes trough a temporal analysis using remote sensing data and obtained optically stimulated luminescence (OSL) dating to understand the genesis of this large anastomosing river and the development of its meandering secondary channels. Scroll bars have developed in a multichannel river system at least since 7.5 ± 0.85 ka. Avulsion is inferred to have played a minor role in the formation of this anastomosing system, with only one documented case while mid‐channel bar formation and chute cut‐offs of the main and secondary channels are the main formative mechanisms of anastomosis in this system. Differences in resistance to erosion control the relatively straight main channel and allow secondary channels to develop a meandering platform. Vegetation contributes to the relative stability of islands and the floodplain. Low gradient and high average aggradation rate (1.1 mm yr−1) are conditions which favor the development of anastomosis. Additionally, stable external conditions, low abandonment rate of older channels and independence from high avulsion frequency suggest a long‐lived, semi‐static type of anastomosing river in this reach of the Amazon. Copyright © 2012 John Wiley & Sons, Ltd.

A comparative study of sediment waves and cyclic steps based on geometries, internal structures and numerical modeling

Although sediment waves cover many levees and canyon floors of submarine fan systems, their relation to the turbidity currents that formed them is still poorly understood. Over the recent years some large erosional sediment waves have been interpreted as cyclic steps. Cyclic steps are a series of slowly upslope migrating bedforms (steps), where each downward step (the lee side of the bedform) is manifested by a steeply dropping flow passing through a hydraulic jump before re-accelerating on the flat stoss side. Here, a general comparison is made between sediment waves and cyclic steps. First, the analogies between their geometries and internal structures are explored. Secondly, a basic numerical model is used to construct stability fields for the formation of cyclic steps. These stability fields are compared with large, existing datasets of both fine- and coarse-grained sediment waves. The numerical results enable an explanation of geometrical trends found over series of sediment waves in the upper part of the Monterey Canyon, on the middle Amazon Fan and on a leveed channel in the Makassar Strait in terms of changes in flow properties of the overriding turbidity current. Based on sedimentological arguments and numerical analysis it is concluded that cyclic steps form a potential alternative for the existing interpretations on the origin of upslope migrating sediment waves.

Two-scale gravitational collapse in the Amazon Fan: a coupled system of gravity tectonics and mass-transport processes

Abstract: Gravity tectonics affects the entire marine sedimentary sequence of the Foz do Amazonas basin, including the topmost Amazon Fan. During the various stages of the margin's evolution, the sedimentary loading and bathymetric slope induced the formation of a linked extensional–compressional system in which gravitational fold-and-thrust belts form significant structural features on the continental slope. Seismic analysis carried out in this study shows that sea-floor relief created along these thrust belts can trigger recurrent mass-transport deposits in the upper–middle Amazon Fan, suggesting a long-lasting linkage between gravity tectonics and mass-transport processes throughout the sedimentary evolution of the Amazon Fan. Supplementary material: Uninterpreted seismic sections are available at http://www.geolsoc.org.uk/SUP18393 .

Uma biografia de Peter Paul Hilbert: a história de quem partiu para ver a Amazônia

Essa biografia conta a história do meu pai, Peter Paul Hilbert (1914-1989), arqueólogo do Museu Paraense Emílio Goeldi, em Belém, que entre 1948 e 1961 pesquisou no médio rio Amazonas. Ele procurava contar histórias sobre os moradores que viviam às margens do rio e suas culturas por meio de uma arqueologia que privilegiava a relação entre pessoas, bem como entre pessoas e o ambiente tropical.

A New Species of Freshwater Crab of The Genus Fredius Pretzmann, 1967 from The Middle Amazon River Basin, Brazil (Crustacea: Decapoda: Pseudothelphusidae)

A new species of pseudothelphusid crab, Fredius ykaa, from the Rio Marau drainage, in the middle Amazon basin, state of Amazonas, Brazil, is described and illustrated. The new species is characterized by a first gonopod with a straight border between the cephalic spine and the apex, as well as by a highly reduced mesial lobe relative to the size of the cephalic spine. The new species is compared with four other species of the genus Fredius Pretzmann, 1967, occurring in the Brazilian Amazon region and its geographical distribution is discussed.