ABUNDANCE AND ISOTOPIC COMPOSITION OF PLANKTONIC MICROCRUSTACEANS IN A CENTRAL AMAZON FLOODPLAIN LAKE: IMPLICATIONS FOR THE TROPHIC DYNAMICS OF THE PLANKTON COMMUNITY

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

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

Wave Propagation Through Non-Uniform Plasma

Increased energy demand has led to plans for building many new dams in the western Amazon, mostly in the Andean region. Historical data and mechanistic scenarios are used to examine potential impacts above and below six of the largest dams planned for the region, including reductions in downstream sediment and nutrient supplies, changes in downstream flood pulse, changes in upstream and downstream fish yields, reservoir siltation, greenhouse gas emissions and mercury contamination. Together, these six dams are predicted to reduce the supply of sediments, phosphorus and nitrogen from the Andean region by 69, 67 and 57% and to the entire Amazon basin by 64, 51 and 23%, respectively. These large reductions in sediment and nutrient supplies will have major impacts on channel geomorphology, floodplain fertility and aquatic productivity. These effects will be greatest near the dams and extend to the lowland floodplains. Attenuation of the downstream flood pulse is expected to alter the survival, phenology and growth of floodplain vegetation and reduce fish yields below the dams. Reservoir filling times due to siltation are predicted to vary from 106-6240 years, affecting the storage performance of some dams. Total CO2 equivalent carbon emission from 4 Andean dams was expected to average 10 Tg y-1 during the first 30 years of operation, resulting in a MegaWatt weighted Carbon Emission Factor of 0.139 tons C MWhr-1. Mercury contamination in fish and local human populations is expected to increase both above and below the dams creating significant health risks. Reservoir fish yields will compensate some downstream losses, but increased mercury contamination could offset these benefits

The potential impact of new Andean dams on Amazon fluvial ecosystems

Increased energy demand has led to plans for building many new dams in the western Amazon, mostly in the Andean region. Historical data and mechanistic scenarios are used to examine potential impacts above and below six of the largest dams planned for the region, including reductions in downstream sediment and nutrient supplies, changes in downstream flood pulse, changes in upstream and downstream fish yields, reservoir siltation, greenhouse gas emissions and mercury contamination. Together, these six dams are predicted to reduce the supply of sediments, phosphorus and nitrogen from the Andean region by 69, 67 and 57% and to the entire Amazon basin by 64, 51 and 23%, respectively. These large reductions in sediment and nutrient supplies will have major impacts on channel geomorphology, floodplain fertility and aquatic productivity. These effects will be greatest near the dams and extend to the lowland floodplains. Attenuation of the downstream flood pulse is expected to alter the survival, phenology and growth of floodplain vegetation and reduce fish yields below the dams. Reservoir filling times due to siltation are predicted to vary from 106–6240 years, affecting the storage performance of some dams. Total CO2 equivalent carbon emission from 4 Andean dams was expected to average 10 Tg y-1 during the first 30 years of operation, resulting in a MegaWatt weighted Carbon Emission Factor of 0.139 tons C MWhr-1. Mercury contamination in fish and local human populations is expected to increase both above and below the dams creating significant health risks. Reservoir fish yields will compensate some downstream losses, but increased mercury contamination could offset these benefits

Reducing adverse impacts of Amazon hydropower expansion

Proposed hydropower dams at more than 350 sites throughout the Amazon require strategic evaluation of trade-offs between the numerous ecosystem services provided by Earth\u27s largest and most biodiverse river basin. These services are spatially variable, hence collective impacts of newly built dams depend strongly on their configuration. We use multiobjective optimization to identify portfolios of sites that simultaneously minimize impacts on river flow, river connectivity, sediment transport, fish diversity, and greenhouse gas emissions while achieving energy production goals. We find that uncoordinated, dam-by-dam hydropower expansion has resulted in forgone ecosystem service benefits. Minimizing further damage from hydropower development requires considering diverse environmental impacts across the entire basin, as well as cooperation among Amazonian nations. Our findings offer a transferable model for the evaluation of hydropower expansion in transboundary basins

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