Lower Amazon Research Articles

Toxic and essential trace element concentrations in the freshwater shrimp Macrobrachium amazonicum in the Lower Amazon, Brazil

This study aimed to evaluate the concentrations of toxic elements (As, Cd, Hg, Pb) and essential trace elements (Co, Cu, Cr, Fe, Mn, Mo, Ni, Se, Zn) in the freshwater shrimp M. amazonicum in the region of Santarem (lower Amazonia), which is affected by mining activities. The level of metal accumulation in the shrimp was found to be similar to that measured in other regions affected by anthropogenic polluted in both in Brazil and elsewhere, and does not pose a significant risk for human consumption. The different patterns of metal accumulation between the Amazon and Tapajos basins appear to be (at least partly) related to respectively bauxite exploitation and gold mining in the region. Bioaccumulation of the trace elements Co, Fe, and Mn mainly occurred in the visceral part of the shrimps from the Amazon river.

Slowing of Caribbean through-flow

Trends in near-surface currents passing through the southeastern Caribbean are described using ocean reanalysis and a coupled model projection. The decline of Caribbean through-flow is linked with tropical and polar forcing. In the upstream zone, the North Brazil Current shows increasing retroflection as the southern Hadley Cell expands across the equatorial Atlantic. This inhibits northwestward transport next to the Amazon River plume. In the downstream zone, the Labrador Current feeds low saline Arctic waters into the Gulf Stream, inducing an equatorward shift and reduced flow.Evidence is growing for spin-down of the North Atlantic gyre and its feeder currents, that inhibit poleward heat exchange and contribute to climatic shifts. Eastward trends of winds and currents in the equatorial Atlantic is projected to bring a drier climate to the lower Amazon basin and southeastern Caribbean, hence greater salinity with knock-on effects for regional sea temperatures.

Clinical and molecular diagnosis of Chlamydophila in captive parrots in Pará State, Brazil

Parrots (Order Psittaciformes) are globally distributed birds that, together with members of the Columbiformes, represent the most susceptible animals, in regards to infection by Chlamydophila psittaci, which is an obligate, zoonotic, intracellular bacterium that causes chlamydiosis in domestic and wild birds and psittacosis in humans. The aim of the present study was to assess the occurrence of C. psittaci in Brazilian psittacids kept in conservation breeding sites in Pará State, Brazil. Cloacal and oropharynx swab samples were collected from 201 psittacids that were distributed among four breeding sites: Metropolitan Area of Belém (C1 and C2), Northeastern Pará (C3), and Low Amazon (C4). The samples were screened for C. psittaci using semi-nested PCR, and the resulting incidence data were analyzed using proportion and chi-square tests. Chlamydophila infection was confirmed for all the breeding sites, with an overall prevalence of 31.84%, and no species-specific predisposition was observed. Furthermore, 13.93% of the sampled birds eliminated the infectious agent by the cloaca, whereas 11.44% eliminated the agent by the oropharynx, and 6.47% eliminated the agent by both routes. Moreover, there was a significant difference between the incidence of Chlamydophila infection of breeding sites C2 and C3 (p=0.029), which yielded the smallest and largest number of diagnosed cases, respectively. In the present study, most of the birds (27.86%) were considered unapparent carriers of Chlamydophila infection, and only 3.98% of the birds yielded both a positive diagnosis and clinical signs of chlamydiosis.

Reproductive biology of Silver Croaker (Plagioscion squamosissimus) species of fishery importance in the Lower Amazon, Pará, Brazil

Fishing is an important commercial activity in the Amazon region. In the Lower Amazon, the species Plagioscion squamosissimus, popularly known as silver croaker, is one of the main commercial fish of the region. The objective of this study was to evaluate the reproductive biology of that species commercialized in Santarem-PA in order to quantify the sex ratio, determine the reproductive period, and estimate the average length at the first sexual maturation (L50). The specimens were collected weekly between August 2014 and July 2015 in the main fish landing port in the city. A total of 314 individuals were sampled, being 170 (54.14%) females and 144 (46.85%) males. The total lengths were higher for females, with no significant difference for gender. The maximum reproductive activity was observed in the end of the drought and in the beginning of the flood season (November, December and February). The total length average considering the first sexual maturity (L50) was estimated in 19,6 cm for females. These results can be translated into information of extreme importance for local fishery management, targeting both conservation and rational use of natural stocks of silver croaker.

Richness, abundance and microhabitat use by Ardeidae (Aves: Pelecaniformes) during one seasonal cycle in the floodplain lakesof the lower Amazon River

The role of morphodynamic features such as grain size, swash climate and wave action on the macrofauna of beaches are well-known. However, few studies have investigated natural disturbances as potential drivers of temporal community variations. In southeastern Brazil, we sampled the intertidal macrofauna of two sandy beaches to test whether seasonal disturbances as the frequency of storm wave events (SWE) and rainfall have significant influence on their composition and abundance. The macrofauna assemblage differed significantly between the rainy and the dry seasons, but rainfall was not the main driver of community changes, although both beaches are in the vicinity of extensive river plumes. Actually, SWE explained most macrofauna richness overtime, with positive effects. Our results point to the importance of learning more about the effects of poorly studied disturbances on macrofaunal communities, and based on them we strongly recommend including these seasonal phenomena when monitoring sandy beaches.

Retrieving Total and Inorganic Suspended Sediments in Amazon Floodplain Lakes: A Multisensor Approach

Remote sensing imagery are fundamental to increasing the knowledge about sediment dynamics in the middle-lower Amazon floodplains. Moreover, they can help to understand both how climate change and how land use and land cover changes impact the sediment exchange between the Amazon River and floodplain lakes in this important and complex ecosystem. This study investigates the suitability of Landsat-8 and Sentinel-2 spectral characteristics in retrieving total (TSS) and inorganic (TSI) suspended sediments on a set of Amazon floodplain lakes in the middle-lower Amazon basin using in situ Remote Sensing Reflectance (Rrs) measurements to simulate Landsat 8/OLI (Operational Land Imager) and Sentinel 2/MSI (Multispectral Instrument) bands and to calibrate/validate several TSS and TSI empirical algorithms. The calibration was based on the Monte Carlo Simulation carried out for the following datasets: (1) All-Dataset, consisting of all the data acquired during four field campaigns at five lakes spread over the lower Amazon floodplain (n = 94); (2) Campaign-Dataset including samples acquired in a specific hydrograph phase (season) in all lakes. As sample size varied from one season to the other, n varied from 18 to 31; (3) Lake-Dataset including samples acquired in all seasons at a given lake with n also varying from 17 to 67 for each lake. The calibrated models were, then, applied to OLI and MSI scenes acquired in August 2017. The performance of three atmospheric correction algorithms was also assessed for both OLI (6S, ACOLITE, and L8SR) and MSI (6S, ACOLITE, and Sen2Cor) images. The impact of glint correction on atmosphere-corrected image performance was assessed against in situ glint-corrected Rrs measurements. After glint correction, the L8SR and 6S atmospheric correction performed better with the OLI and MSI sensors, respectively (Mean Absolute Percentage Error (MAPE) = 16.68% and 14.38%) considering the entire set of bands. However, for a given single band, different methods have different performances. The validated TSI and TSS satellite estimates showed that both in situ TSI and TSS algorithms provided reliable estimates, having the best results for the green OLI band (561 nm) and MSI red-edge band (705 nm) (MAPE < 21%). Moreover, the findings indicate that the OLI and MSI models provided similar errors, which support the use of both sensors as a virtual constellation for the TSS and TSI estimate over an Amazon floodplain. These results demonstrate the applicability of the calibration/validation techniques developed for the empirical modeling of suspended sediments in lower Amazon floodplain lakes using medium-resolution sensors.

Commercial traceability of <i>Arapaima</i> spp. fisheries in the Amazon basin: can biogeochemical tags be useful?

Abstract. The development of analytical tools to determine the origin of fishes is useful to better understand patterns of habitat use and to monitor, manage, and control fisheries, including certification of food origin. The application of isotopic analyses to study calcified structures of fishes (scales, vertebrae, and otoliths) may provide robust information about the fish geographic origin and environmental living conditions. In this study, we used Sr and C isotopic markers recorded in otoliths of wild and farmed commercialized pirarucu (Arapaima spp.) to evaluate their prediction potential to trace the fishes origin. Wild and farmed fish specimens, as well as food used for feeding pirarucu in captivity, were collected from different sites. Isotope composition of otoliths performed by isotope-ratio mass spectrometry (IRMS; δ13C) and femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (LAfs-MC-ICPMS; 87Sr∕86Sr) were compared to the isotopic composition of water and of the food given to the fishes in the farms. Wild fish specimens that lived in environments with the largest fluctuation of river water Sr isotope ratios over time presented the largest Sr isotope variations in otoliths. A quadratic discriminant analysis on otolith isotopic composition provided 58 % of correct classification for fish production (wild and farmed) and 76 % of correct classification for the fish region. Classification accuracy for region varied between 100 % and 29 % for the Madeira and the Lower Amazon fishes, respectively. Overall, this preliminary trial is not yet fully developed to be applied as a commercial traceability tool. However, given the importance of Arapaima spp. for food security and the generation of economic resources for millions of people in the Amazon basin, further analyses are needed to increase the discrimination performance of these biogeographical tags.

Retraction: Solar-Aligned Pictographs at the Paleoindian Site of Painel do Pilão along the Lower Amazon River at Monte Alegre, Brazil.

Retraction: Solar-Aligned Pictographs at the Paleoindian Site of Painel do Pilão along the Lower Amazon River at Monte Alegre, Brazil.

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

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

Desenvolvimento inicial de espécies arbóreas em sistemas agroflorestais no Baixo Amazonas, Pará, Brasil

Estudos sobre o desenvolvimento inicial de espécies arbóreas em sistemas agroflorestais são importantes, pois fornecem subsídios para o manejo desses agroecossistemas. O objetivo dessa pesquisa foi avaliar a sobrevivência e o crescimento em altura de mudas de espécies arbóreas em sistemas agroflorestais amazônicos submetidos a diferentes formas de preparo da área e manejo. O experimento foi conduzido em dois sistemas agroflorestais (sucessional e consórcio agroflorestal) localizados no Baixo Amazonas, oeste do estado do Pará. No consórcio agroflorestal comercial, a taxa de sobrevivência das espécies não ultrapassou o valor de 70%. No sistema sucessional a taxa de sobrevivência das espécies arbóreas implantadas foi alta com a maioria variando entre 90 a 100%. O estresse hídrico nos períodos mais secos do ano é um fator limitante na adoção de sistemas agroflorestais na região causando mortalidade das mudas. Quanto ao crescimento em altura, as espécies avaliadas obtiveram desempenhos satisfatórios em ambos os sistemas.

Diversity in reproductive traits of arapaima (Arapaima spp., Müller, 1843) in Amazonian várzea floodplains: Conservation implications

Abstract Understanding the reproductive ecology of freshwater fishes is essential to minimize the losses in global freshwater biodiversity but is often limited in data‐poor regions, such as tropical floodplain ecosystems. Specifically, the study investigated whether size at first sexual maturation and nesting features for arapaima vary within and across regions in the floodplain of the Amazon River. Data were collected at several sites in the Lower Amazon with varying arapaima densities and fishing practices. Female gonads were examined from commercial catch to calculate total length of first sexual maturation (L50). Nest features were surveyed in the field. The size at first maturation and nest features (i.e. nest morphology, habitat, and density) were compared among sites with different population densities in the Lower Amazon and among estimates drawn from the literature for other regions. In the Lower Amazon, L50 showed significant variation between high‐density (139 cm) and other sites (~168 cm). Overall variation in L50 estimates for arapaima range from 139 cm in the Lower Amazon to 207 cm in the Upper Amazon in Peru. Nests in different regions show variation among certain nest features and a positive relationship between nest density and arapaima population density. In the Lower Amazon, 90% of nests were found under woody vegetation. The results show considerable diversity in size at first maturity and nesting features for arapaima. This suggests that there may be multiple evolutionarily significant units or species, even within the study area. This study also illustrates the importance of forest cover to arapaima spawning. Furthermore, different nesting morphologies were found at different sites. There are meaningful variations in arapaima reproductive behaviour, both locally and basin‐wide, that require further study as they have implications for effective management and conservation initiatives.

Occurrence and distribution of Diaphorina citri (Hemiptera: Liviidae) and Tamarixia radiata (Hymenoptera: Eulophidae) in Pará state, Brazil

ABSTRACT: This study presents and discusses the results of a survey for the presence of Diaphorina citri Kuwayama and its natural enemies in Citrus spp. citrus and Murraya sp. myrtle plants in Pará State, Brazil. From 2013 to 2017, observations were made in five mesoregions of the State, and where D. citri was present, branches were examined to quantify eggs, nymphs and mummies with parasitoid emergence holes and to obtain parasitoids. D. citri adults were used to detected the bacterium through nested polymerase chain reaction (NESTED-PCR). Psyllids were found in citrus and myrtle plants. A total of 583 parasitoid specimens of Tamarixia radiata (Waterston) were obtained. The bacterial detection test was negative for Candidatus Liberibacter spp. Psyllids and parasitoids were present in the Lower Amazon, Metropolitan area, Northeastern Pará, Southeastern Pará and Southwestern Pará mesoregions. The presence of D. citri in citrus, with was previously absent in this host, alters the risk situation for Huanglongbing (HLB) in the State. These results will aid in developing preventive or containment measures through phytosanitary protection.

Discipline and Develop: Destruction of the Brazil Nut Forest in the Lower Amazon Basin

This article considers Amazonian environmental change by focusing on political and economic processes in a place-specific context with far-reaching global implications. In particular, we consider the destruction of the Brazil nut forest (BNF) in the lower basin. The Brazil nut tree yields a valuable nontimber forest product, and its loss raises concerns about Amazonia’s agro-ecological sustainability. The article posits the destruction of the BNF as an outcome of land creation, the transformation of soil surfaces into a production factor for market-oriented agriculture. Land creation in the lower basin sparked violent conflict, with the destruction of the BNF as collateral damage. Our account complements earlier research on the political economy of Amazonian development by providing an update tuned to the institutional and economic changes that have led to the region’s engagement with globalized beef markets and to the transformative impact on implicated actors (i.e., peasant, capital, and the state). In addition, the article uses the BNF case to consider current threats to Amazonia. In Brazil, deforestation rates declined after the turn of the millennium, due to environmental policy. Recent numbers show deforestation on the rise, however, as South American nations fast-track large infrastructure projects to transform Amazonia into a transport hub and a continental source of hydropower. The article questions whether Brazil’s environmental policies will sustain the Amazonian forest over the long run; the BNF disappeared despite efforts at conservation buttressed by legislative action. The article uses data from surveys, remote sensing, regional newspapers, and secondary sources based on declassified documents from Brazil’s Armed Forces, the National Truth Commission, and the Central Intelligence Agency (CIA). Key Words: Amazon, deforestation, IIRSA, land grab, resource conflict, sustainable development.

Size-structured habitat selection by arapaima in floodplain lakes of the Lower Amazon

Human modification of floodplain ecosystems is widespread and a major threat to fish populations, particularly in the tropics where fish diversity and rates of floodplain degradation are high. Identifying measures to minimize the susceptibility of floodplain fishes to habitat modification requires understanding dry‐season lake habitat selection for species of conservation concern. This study examined the effects of environmental factors on dry‐season floodplain lake habitat selection by arapaima (Arapaima spp.) and determined the extent to which they differed across three size classes. In floodplain lakes of the lower Amazon River, variables were measured at locations representing habitat availability and compared with measurements taken where arapaima were observed during surface breathing. Regression models were used to account for between‐lake variation in the presence of arapaima owing to nearby fishing communities. The probability of arapaima presence at each sample location was modelled based on the variables measured. The results indicated that arapaima expressed distinct habitat selection patterns, which differed significantly across size classes. The general pattern observed was that all arapaima were more likely to be found in deeper, more turbid, and higher conductivity locations, whereas smaller arapaima were more likely to remain near dense beds of floating macrophytes. The probability of arapaima presence differed among fishing community territories, reflecting differences in management schemes. Deeper, macrophyte‐rich sections of floodplain lakes appear to provide key habitats for arapaima and deserve consideration for becoming priority targets for conservation of the rich diversity of fish species in these systems.

Stratification and mixing in large floodplain lakes along the lower Amazon River

Abstract Large, shallow lakes are common in the extensive floodplains throughout the tropics. To determine controls on their mixing dynamics, we instrumented 5 stations in two shallow, connected tropical lakes on the lower Amazon floodplain with meteorological and temperature sensors. A tight relation between changes in thermal structure and LMO/h (the ratio of the Monin-Obukhov length scale to the depth of the actively mixing layer) indicates the sensitivity of thermal structure to wind speed relative to heating and cooling. Four regimes led to variations in mixing: (i) high solar radiation with light winds in the mid-morning to early afternoon resulted in shallow stratification, 0 1; (iii) by late afternoon, buoyancy flux became negative and LMO/h 0.06 m s−1, mixing from wind and cooling co-occurred; and (iv) convection dominated mixing on nights with light winds, −1

AVALIAÇÃO DO COMPORTAMENTO DE BOVINOS E BUBALINOS DURANTE EXPOSIÇÃO FEIRA AGROINDUSTRIAL DO BAIXO AMAZONAS

Objetivou-se avaliar as principais alterações comportamentais dos animais confinados na feira agropecuária. O trabalho foi conduzido nas dependências do Parque de exposição Alacid Nunes, durante a XXXIX Feira Agroindustrial do Baixo Amazonas de 2016. Foram observados os comportamentos de ócio, alimentando, ruminando de 8 (oito) bovinos e 8 (oito) bubalinos, com pesos e idades semelhantes. No parque de exposições os animais foram alojados em duas baias de 4x4m², com bebedouros e comedouros, com cobertura de telhas de fibrocimento, com altura de 3m. Para a análise estatística, foi utilizado o teste de T de Student, a 5% de probabilidade, por meio do software MINITAB® 2014. O tempo despendido para ócio foi diferente entre bovinos e bubalinos no momento 21h (12,00±9,37 x 9,38±6,20). O tempo despendido na ruminação foi maior em bubalinos nos tempos 09h (4,09±5,30 x 10,00±10,65), 15h (6,13±8,97 x 10,58±8,56) e 21h (16,04±9,65 x 12,29±5,74), os bubalinos passaram mais tempo ruminando no horário mais frio do dia 06h (11,53±10,91 x 16,43±11,78). O pico de alimentação realizado pelos bovinos foi observado 9h (11,69±8,67 x 3,84±7,00) e para bubalinos o pico de alimentação às 21h (1,45±2,18 x 7,17±5,35). Do tempo total de ócio dos bubalinos, 77,02% ocorreu com animais em postura deitado e 17,27% em Pé. Por sua vez os bovinos apresentaram 69,75% desta atividade em Pé e 30,25% deitados. Conclui-se, que bovinos dispensam mais tempo nas atividades de alimentação, ócio e ruminação durante períodos mais quentes do dia, em contrapartida os bubalinos realizam suas atividades nos momentos mais frios do dia.PALAVRA-CHAVE: Búfalos, Comportamento, Estresse térmico, Nelore.

Parotocinclus yaka, a new species of armored catfish (Loricariidae: Hypoptopomatinae), from the Amazon basin in Brazil.

Parotocinclus yaka is described as a new species of hypoptopomatine cascudinho from tributaries of the Rio Tiquié, tributary to the Rio Uaupés, upper Rio Negro drainage, Amazon basin, Amazonas State, Brazil. The new species is distinguished from its congeners in northeastern and southeastern Brazil by having the cheek canal plate elongated posteriorly on the ventral surface of the head and in contact with the cleithrum. Parotocinclus yaka is diagnosed from the Parotocinclus species of the Amazon, Orinoco and Guianas watersheds by having a conspicuous dark spots smaller than the pupil diameter distributed dorsally and laterally on the head; it is also differentiated from P. polyochrus (Casiquiare, Venezuela), P. longirostris (Rio Amazonas, Brazil), and P. eppleyi (Río Orinoco) by the absence of a Y-shaped light mark dorsally on the head. In addition, the absence of premaxillary and dentary accessory teeth and the presence of a Y-shaped spot on the snout distinguish the new species from P. collinsae (Essequibo River, Guyana), P. halbothi (Rio Trombetas, Brazil and Marowijne River, Suriname) and P. variola (Río Amazonas, Colombia). Parotocinclus yaka also differs from P. amazonensis (lower Amazon basin), P. aripuanensis (lower Amazon basin), P. britskii (Guyana, Suriname, eastern Venezuela, and Amapá State, Brazil), and P. dani (Rio Tapajós basin), by having more numerous oral teeth. The new species described herein is part of the group of small cascudinhos usually associated with marginal or submerged vegetation and submerged logs, of moderate current and clear transparency, found in conserved habitats in streams of the Amazon, Orinoco and Guianas rivers.

A new species of Bryconops Kner (Characiformes: Iguanodectidae) from the Rio Maicuru, lower Amazon basin, Brazil.

A new species of Bryconops is described from the rio Maicuru, a tributary of the left margin of the lower Amazon River, Pará, Brazil. Bryconops chernoffi new species, differs from all its congeners by the presence of an elongated dark patch of pigmentation immediately after the posterodorsal margin of the opercle, running vertically from the supracleithrum to the distal margin of the cleithrum (vs. absence of a similar blotch), and by a dark dorsal fin with a narrow hyaline band at middle portion of dorsal-fin rays (vs. dorsal fin hyaline or with few scattered chromatophores). It differs further from all its congeners, except B. colanegra, by the presence of a blurred black stripe at the anal fin base. It differs from B. colanegra by possessing fewer predorsal scales (8-9 vs. 10-11) and in that the third infraorbital contacts the preopercle ventrally (vs. third infraorbital not contacting preopercle ventrally). The new species is assigned to the subgenus Creatochanes by the number of maxillary teeth, and ossification and denticulation of the gill rakers.

A relação entre a variação hidrológica e os recursos pesqueiros no baixo Amazonas, Santarém, Pará (The Relationship between Hydrologic Variation and Fishery Resources at the Lower Amazon, Santarém, Pará)

Na Amazônia, as grandes flutuações do nível dos rios modulam a pesca e influenciam no quantitativo capturado pelos pescadores. Nesse sentido, objetivou-se caracterizar e avaliar o efeito da variação hidrológica sobre os recursos pesqueiros no município de Santarém, Pará. As informações sobre as espécies do pescado desembarcado foram obtidas por entrevistas realizadas com os pescadores no período de 2014 a 2015. Fases hidrológicas foram caracterizadas com base nos dados da estação hidrometeorológica de Santarém, disponibilizados pela ANA (2000 a 2015). A relação entre as espécies registradas e as variáveis ambientais (cota, precipitação e temperatura da água) foi verificada pela Análise de Correspondência Canônica (CCA). Observou-se que a flutuação sazonal do rio Tapajós é definida por quatro fases (enchente, cheia, vazante, seca), sendo que a cheia (7,77 m) e seca (2,28 m) são períodos extremos. Os menores volumes de produção de pescado ocorreram de dezembro a fevereiro, enquanto que os meses de abril e setembro apresentaram os maiores volumes. Nos meses de março a junho, prevalecem espécies das famílias Anostomidae, Prochilodontidae, Characidae e Pimelodidae, em novembro e dezembro (seca) a família Pimelodidae. Os dois primeiros eixos da CCA explicaram 52,4% da relação entre as espécies e variáveis, indicando que o período hidrológico é determinante na variação sazonal do pescado. Assim, o entendimento das variáveis hidrológicas junto aos recursos pesqueiros, são subsídios para auxiliar a gestão e o ordenamento da atividade. A B S T R A C TIn the Amazon, large fluctuations in rivers’ level modulate fishing and influence the quantity captured by fishermen. The objective of this study was to characterize and evaluate the effect of hydrological variation on fishery resources in the municipality of Santarém, Pará. Information on the fish species landed was obtained by interviews with fishermen from December 2013 to January 2015. Hydrological phases were characterized based on data from the Santarém hydrometeorological station (2000 to 2015). The relationship between the recorded species and environmental variables (water height, rainfall, water temperature) was verified by Canonical Correspondence Analysis (CCA). It was observed that the seasonal fluctuation of the Tapajós River is defined by four phases (rising, flood, lowing, dry), and the flood (7.77 m) and dry (2.28 m) are extreme periods. The lower volumes of production occurred from December to February, while the months of April and September presented the highest volumes. From March to June, species of the families Anostomidae, Prochilodontidae, Characidae and Pimelodidae prevail, in November and December (dry), only the family Pimelodidae. The first two axes of the CCA explained 52.4% of the relation between species and environmental variables, indicating that the hydrological period is determinant in the seasonal variation of the fish. Thus, the understanding of the hydrological variables along with the fishing resources, are subsidies for the better management of the activity.Keywords: Hydrology, Tapajós River, Fishery.

Are seasonal variations in river-floodplain sediment exchange in the lower Amazon River basin resolvable through meteoric cosmogenic 10Be to stable 9Be ratios?

The lower Amazon basin contains vast floodplains that exchange sediment with the main river. The exchange of sediment between the floodplain and the channel follows a seasonal cycle that is anticorrelated with the hydrological cycle. At low water stages, sediment that has been stored in the floodplain for potentially several thousands of years is eroded and transferred from the floodplain to the mainstem. During high water stages, most sediment transported in the main channel stems directly from the eroding source with little intermittent storage. We apply the meteoric cosmogenic 10Be to stable 9Be ratio (10Be/9Be) as a denudation and weathering proxy to investigate this seasonality in sediment transport. Single meteoric 10Be concentrations ([10Be]) have previously been shown to record floodplain storage; whereas fractions of mobilized 9Be, a trace metal released during weathering, provide degrees of weathering. The resulting 10Be/9Be ratio provides denudation rates of the sediment sources. We compare 10Be/9Be measured on suspended sediment from river depth profiles at two sites (Óbidos/Macapa) and during two hydrological seasons (high/low water stage in 2013). We show that careful construction of river depth profiles in combination with Rouse modeling is necessary to exclude the grain size dependence that together with hydrodynamic sorting introduces a bias into single [10Be] and [9Be]. In contrast, the 10Be/9Be is largely uniform across grain sizes and is thus unaffected by sorting. Our 10Be/9Be ratios, the denudation rates derived from them, and mobilized 9Be fractions do not show variations outside their uncertainties across seasons or sites. Thus, 10Be/9Be show that upstream sediment sources were well mixed by multiple cycles of storage and remobilization in the floodplain.