Carbon dioxide and methane emissions from interfluvial wetlands in the upper Negro River basin, Brazil

Extensive interfluvial wetlands occur in the upper Negro River basin (Brazil) and contain a mosaic of vegetation dominated by emergent grasses and sedges with patches of shrubs and palms. To characterize the release of carbon dioxide and methane from these habitats, diffusive and ebullitive emissions and transport through plant aerenchyma were measured monthly during 2005 in permanently and seasonally flooded areas. CO2 emissions averaged 2193 mg C m-2 day-1. Methane was consumed in unflooded environments and emitted in flooded environments with average values of -4.8 and 60 mg C m-2 day-1, respectively. Bubbles were emitted primarily during falling water periods when hydrostatic pressure at the sediment-water interface declined. CO2 and CH4 emissions increased when dissolved O2 decreased and vegetation was more abundant. Total area and seasonally varying flooded areas for two wetlands, located north and south of the Negro River, were determined through analysis of synthetic aperture radar and optical remotely sensed data. The combined areas of these two wetlands (3000 km2) emitted 1147 Gg C year-1 as CO2 and 31 Gg C year-1 as CH4. If these rates are extrapolated to the area occupied by hydromorphic soils in the upper Negro basin, 63 Tg C year-1 of CO2 and 1.7 Tg C year-1 as CH4 are estimated as the regional evasion to the atmosphere. © 2010 The Author(s)

Mercury Concentrations in Fishes of the Madeira River: Results and Recomendations for Human Consumption

Samples of eleven fish species were collected during September and October of 1991 in the gold mining area of Cachoeira de Teotônio and in the control area Guajará-Mirim, along the Madeira River, (Rondônia, Brazil) and anaiized for total mercury by cold vapor atomic absorption spectrofotometry. Almost all fish predators from the gold mining area had mercury concentrations above the maximal level of 0.5 ug.g"1, permitted for human consumption by Brazilian Secretary of Health and the World Health Organization and much greater than those found in predatory fish species in the control area were all below this critical value (0.5 pg.g\'X demonstrating the influence of anthropogenic contamination in the gold mining area. In both areas, non-predators fish species had lower mercury concentrations than predators fish species, indicating the effects of biomagnification of mercury in the food chain. Safety limits for fish consumption by the human populations in this gold mining area were estabilished considering the mercury levels encontred in fish and the critical intake rate associated with the signs of mercury poisoning. Pacu, could be consumed without restrictions, matrinchã, curimatã, mandi and tucunaré, could be consumed with moderation and large predatory fish species (mostly Siluriformes), could be consumed only sporadically. Some factors that could influence mercury contaminations in "ribeirinhos" are discussed.A concentração de mercúrio total foi determinada em onze espécies de peixes coletados de setembro a outubro de 1991, na área de garimpo de ouro da Cachoeira de Tcotônio e da área considerada controle em Guajará-Mirim, ambas no rio Madeira, Estado de Rondônia. Utilizou-se, para a análise, a técnica de espectrofotometria de absorção atômica com gerador de vapor frio de Hg. Quase todos os peixes predadores da área de garimpo tiveram concentrações de mercúrio acima do nível critico de 0,5 pg.g"1 permitido para consumo humano pelo Ministério da Saúde do Brasil e Organização Mundial de Saúde, sendo bem maiores que as concentrações de mercúrio nas espécies predadoras da área controle, evidenciando a influência do garimpo de ouro na contaminação dos peixes por mercúrio. As espécies não-predadoras tiveram concentrações de mercúrio abaixo daquelas das espécies predadoras para as duas áreas, indicando o efeito da biomagnificação do mercúrio na cadeia alimentar. Procurou-se estabelecer limites para o consumo de peixes pelas populações humanas da área de garimpo estudada, calculando-se a taxa de ingestão necessária para se desenvolver os primeiros sintomas de contaminação mercurial. Concluiu-se que espécies como o pacu podem ser consumidas sem restrição, já os peixes como matrinchã, curimatã, mandi e tucunaré, deveriam ser consumidos com moderação e que a maioria dos peixes predadores (em geral Siluriformes), deveriam ser consumidos apenas esporadicamente. Discutem-se alguns fatores que poderiam estar interagindo no processo de contaminação por mercúrio dos ribeirinhos dessa área de garimpo

Variación estacional de la distribución y composición isotópica del fitoplancton en un lago de inundación en la amazonia, Brasil

To evaluate the seasonal variation and isotopic composition of phytoplankton, water samples were collected monthly between October 2007 and November 2008 in Lake Catalão, a floodplain lake at the confluence between rivers Negro and Amazon. Analyses of total chlorophyll concentration and δ13C and δ15N isotopic abundances were made from particulate size fractions of 30-60, 10-30 and <10 μm in the littoral, pelagic, and floating meadows regions. Chlorophyll concentration was found to be inversely associated to lake depth, and high concentrations of chlorophyll in the floating meadows zone were significant. The fraction <10 μm was the most abundant representing in average more than 40 % of the particulate matter. The δ13C values were relatively constant during the study (-25.1 ‰ ~ -34.0 ‰), whereas the δ15N values showed strong variability (15.6 ‰ ~ 2.4 ‰), which has been attributed to the resuspension of sediments during mixing of the water column. Mixing associated to the sudden drop in temperature during the rising water period was an important event in the trophic and isotopic dynamics of the lake. Variations in chlorophyll content were generally associated with the dilution process, in which concentration was inversely correlated to the water level, whereas abundance was directly correlated to the water level

Abundancia y composición isotópica de los microcrustáceos planctónicos en un lago de inundación de la Amazonía Central: Implicaciones para la dinámica trófica de la comunidad planctónica

During the hydrological year from December 2007 to November 2008, monthly samplings in the pelagic, littoral and macrophytes zones were conducted in the Lago Catalão, a floodplain lake receiving a mixture of water from Negro and Solimões Rivers, in front of Manaus city. Taxonomic composition and their relative abundance of the planktonic microcrustaceans community was studied. Natural abundances of carbon (C) and nitrogen (N) stable isotopes were measured to indicate energy sources. Cladocerans were the most abundant, with a relative abundance of 60%, followed by the calanoid and cyclopoid copepods with relative abundances of 29% and 11%, respectively. Diaphanosoma spp. was the dominant cladoceran group during all the sampling periods. Cladocerans were also represented by Moina spp., Ceriodaphnia spp. and Daphnia gessneri. Three genera of calanoid copepods were found: Notodiaptomus spp, Rhacodiaptomus spp., and Argyrodiaptomus spp. The genus Mesocyclops spp. was identified among the cyclopoid copepods. Zooplankton δ13C values indicated that the aquatic macrophyte zone was distinct, with a mean of -27.31‰, which was more enriched than zooplankton in the pelagic and littoral zones, where they had mean δ13C values of -33.11 and -34.66‰, respectively. Overall, analysis of stable isotopes showed that regardless of the pathways, the initial source of carbon for the zooplankton was phytoplankton, with a minimal participation of heterotrophic bacteria. © 2016, Universidad Nacional de Colombia. All rights reserved

Mortalidade de tucunaré associada à pesca esportiva do pesque e solte no rio Negro, Amazonas, Brasil

Sport fishing for peacock bass Cichla spp. in the Brazilian Amazon has increased in popularity and attracts anglers who generate significant economic benefits in rural regions. The sustainability of this fishery is partly dependent on the survival of fish caught through catch-and-release fishing. The objective of this work was to investigate, hooking mortality of Cichla spp., including speckled peacock bass (C. temensis Humbolt), butterfly peacock bass (C. orinocensis Humbolt), and popoca peacock bass (C. monoculus Agassiz) in the basin of the Negro River, the largest tributary of the Amazon River. Fish were caught at two different sites using artificial lures, transported to pens anchored in the river and monitored for 72 hours. A total of 162 individual peacock bass were captured and hooking mortality (mean % ± 95% confidence intervals) was calculated. Mean mortality was 3.5% (± 5.0), 2.3% (± 3.5) and 5.2% (± 10.2) for speckled peacock bass, butterfly peacock bass, and popoca peacock bass, respectively. Lengths of captured fish ranged from 26 to 79 cm (standard length), however, only fish under 42 cm died. This research suggests that catch-and-release sport fishing of peacock bass does not result in substantial mortality in the Negro River basin.A pesca esportiva de tucunarés Cichla spp., na Amazônia brasileira, aumentou em popularidade nos últimos anos e tem atraído pescadores esportivos que geram benefícios econômicos para essa região. Entretanto, a sustentabilidade dessa pescaria depende em parte da sobrevivência dos peixes capturados por meio da prática do pesque e solte. O objetivo deste trabalho foi avaliar a mortalidade de Cichla spp., incluindo o tucunaré paca (C. temensis Humbolt), o borboleta (C. orinocensis Humbolt) e o popoca (C. monoculus Agassiz) em dois locais na bacia do rio Negro, o maior tributário do rio Amazonas. Os peixes foram capturados por variados tipos de iscas artificiais e posteriormente monitorados em viveiros construídos no próprio rio por 72 horas. Um total de 162 tucunarés foi capturado, e as mortalidades (% ± intervalo de confiança 95%) foram calculadas. A mortalidade foi 3,5% (± 5,0), 2,3% (± 3,2) e 5,2% (±10,2) para o paca, o borboleta e o popoca, respectivamente. O comprimento padrão dos peixes capturados variou de 26 a 79 cm, mas apenas os peixes menores até 42 cm morreram. A pesquisa sugere que a pesca esportiva não causou substancial mortalidade na população de Cichla spp. na bacia do rio Negro

Turbulence and Gas Transfer Velocities in Sheltered Flooded Forests of the Amazon Basin

Seasonally flooded forests along tropical rivers cover extensive areas, yet the processes driving air-water exchanges of radiatively active gases are uncertain. To quantify the controls on gas transfer velocities, we combined measurements of water-column temperature, meteorology in the forest and adjacent open water, turbulence with an acoustic Doppler velocimeter, gas concentrations, and fluxes with floating chambers. Under cooling, measured turbulence, quantified as the rate of dissipation of turbulent kinetic energy (ε), was similar to buoyancy flux computed from the surface energy budget, indicating convection dominated turbulence production. Under heating, turbulence was suppressed unless winds in the adjacent open water exceeded 1 m/s. Gas transfer velocities obtained from chamber measurements ranged from 1 to 5 cm/hr and were similar to or slightly less than predicted using a turbulence-based surface renewal model computed with measured ε and ε predicted from wind and cooling. ©2019. The Authors

Mercury bioaccumulation in fish of commercial importance from different trophic categories in an Amazon floodplain lake

Thirty-two species of commercially important fish from three trophic levels and nine trophic categories were sampled at a floodplain lake of the Solimões River (Lago Grande de Manacapuru). The fish were analyzed to determine their Hg level and the bioaccumulation, bioconcentration, and biomagnification of this element. The observed increase in mean concentration of mercury (49.6 ng.g -1 for omnivores, 418.3 ng.g -1 for piscivores, and 527.8 ng.g -1 for carnivores/necrophages) furnished evidence of biomagnification. Primary, secondary, and tertiary consumers presented biomagnification factors of 0.27, 0.33, and 0.47, respectively. Significant differences in the bioconcentration and concentration of total Hg occurred between the categories of the third trophic level and the other categories. Plagioscion squamosissimus (carnivorous/piscivorous) and Calophysus macropterus (carnivorous/ necrophagous) showed levels of total Hg above those permitted by Brazilian law (500 ng.g -1). Six other species also posed risks to human health because their Hg levels exceeded 300 ng.g -1. Fifteen species showed bioaccumulation, but only eight presented significant correlations between the concentration of Hg and the length and/or the weight of the fish. © 2011 Sociedade Brasileira de Ictiologia

Diffusive methane fluxes from Negro, Solimões and Madeira rivers and fringing lakes in the Amazon basin

The first extensive set of measurements of methane concentrations and fluxes for the Negro River and its major tributaries combined with complementary data for the Solimões and Madeira rivers and several tributaries are presented and their temporal and spatial variations examined. Fluxes were measured using floating chambers, and dissolved CH4 concentrations were measured by the headspace technique. In the Solimões basin, tributaries had higher fluxes when water levels were low; no statistical difference among periods for lakes and the main stem river was observed. In the Negro basin, rivers had higher fluxes with greater variations among rivers during high water than during low water based on fluxes calculated from the concentration gradient and modelled gas transfer coefficients. We estimate a regional methane emission of 0.31 Tg C yr−1 for large river channels in the lowland Amazon basin. © 2016 Association for the Sciences of Limnology and Oceanograph

Fish species richness is associated with the availability of landscape components across seasons in the Amazonian floodplain

Understanding environmental biodiversity drivers in freshwater systems continues to be a fundamental challenge in studies of their fish assemblages. The present study seeks to determine the degree to which landscape variables of Amazonian floodplain lakes influences fish assemblages in these environments. Fish species richness was estimated in 15 Amazonian floodplain lakes during the high and low-water phases and correlated with the areas of four inundated wetland classes: (i) open water, (ii) flooded herbaceous, (iii) flooded shrubs and (iv) flooded forest estimated in different radius circular areas around each sampling site. Data were analyzed using generalized linear models with fish species richness, total and guilds as the dependent variable and estimates of buffered landscape areas as explanatory variables. Our analysis identified the significance of landscape variables in determining the diversity of fish assemblages in Amazonian floodplain lakes. Spatial scale was also identified as a significant determinant of fish diversity as landscape effects were more evident at larger spatial scales. In particular, (1) total species richness was more sensitive to variations in the landscape areas than number of species within guilds and (2) the spatial extent of the wetland class of shrubs was consistently the more influential on fish species diversity

An explicit GIS-based river basin framework for aquatic ecosystem conservation in the Amazon

Despite large-scale infrastructure development, deforestation, mining and petroleum exploration in the Amazon Basin, relatively little attention has been paid to the management scale required for the protection of wetlands, fisheries and other aspects of aquatic ecosystems. This is due, in part, to the enormous size, multinational composition and interconnected nature of the Amazon River system, as well as to the absence of an adequate spatial model for integrating data across the entire Amazon Basin. In this data article we present a spatially uniform multi-scale GIS framework that was developed especially for the analysis, management and monitoring of various aspects of aquatic systems in the Amazon Basin. The Amazon GIS-Based River Basin Framework is accessible as an ESRI geodatabase at doi:10.5063/F1BG2KX8. © Author(s) 2016