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1. Seasonal and spatial variability of CO2 in aquatic environments of the central lowland Amazon basin.

   https://doi.org/https://doi.org/10.1007/s10533-019-00554-9(01234567.  

   Amaral, J.H.F.; Farjalla, V.F.; Melack, J.M.; Kasper, D.; Scofield, V.; Barbosa, P.M.; Forsberg, B.R. (February 2019, Biogeochemistry)

   Different sources and processes contribute to pCO2 and CO2 exchange with the atmosphere in the rivers and floodplains of the Amazon basin. We measured or estimated pCO2, CO2 fluxes with the atmosphere, planktonic community respiration (PCR), and environmental and landscape variables along the Negro and Amazon-Solimões rivers during different periods of the fluvial hydrological cycle. Values of pCO2 ranged from 307 to 7,527 μatm, while CO2 fluxes ranged from -9.3 to 1,128 mmol m-2 d-1 in the Amazon-Solimões basin. In the Negro basin, pCO2 values ranged from 648 to 6,526 μatm, and CO2 fluxes from 35 to 1,025 mmol m-2 d-1. In a general linear model including data from Negro and Amazon-Solimões basins, seasonal and spatial variation in flooded vegetated habitat area, dissolved oxygen, depth and water temperature explained 85% of surface pCO2 variation. Levels of pCO2 varied with inundation extent, with higher pCO2 values occurring in periods with greater water depth and inundation area, and lower dissolved oxygen concentrations and water temperatures. In a separate analysis for the Amazon-Solimões river and floodplains, ecosystem type (lotic or lentic), hydrological period, water temperature, dissolved oxygen, depth and dissolved phosphorus explained 83% of pCO2 variation. Our results demonstrate the influence of alluvial floodplains and seasonal variations in their limnological characteristics on the pCO2 levels in river channels of the lowland Amazon. 

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

   https://doi.org/10.7717/peerj.5080  

   Carvalho Freitas, Carlos Edwar; Laurenson, Laurie; Yamamoto, Kedma Cristine; Forsberg, Bruce Rider; Petrere, Miguel; Arantes, Caroline; Siqueira-Souza, Flavia Kelly (January 2018, PeerJ)

   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. 

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3. Inundation, hydrodynamics and vegetation influences carbon dioxide concentrations in Amazon floodplain lakes

   https://doi.org/10.1007/s10021-021-00692-y  

   Amaral, J.H.F.; Melack, J.M.; Barbosa, P.M.; Borges, A.V.; Kasper, D.; Cortes, A.C.; Zhou, W.; MacIntyre, S.; Forsberg, B.R. (January 2021, Ecosystems)

   Extensive floodplains and numerous lakes in the Amazon basin are well suited to examine the role of floodable lands within the context of the sources and processing of carbon within inland waters. We measured diel, seasonal and inter-annual variations of carbon dioxide concentrations and related environmental variables in open water and flooded vegetation and estimated the extension of these habitats using remote sensing in a representative central Amazon floodplain lake, Lake Janauacá. Depth-averaged values of CO2 in the open water of the lake, 157± 91 µM (mean ± SD), were less than those in an embayment near aquatic vegetation, 285±116 µM, and were variable over 24-h periods at both sites. Within floating herbaceous plant mats, mean concentration (without one outlier) was 275±77 µM and in flooded forests mean concentration was 217±78 µM. Variability in CO2 concentrations in open water resulted from changes in the extent of inundation and exchange with vegetated habitats. The best statistical model, including CO2 in aquatic plant mats, Secchi depth, rate of change in water level and chlorophyll concentrations, explained around 90% of the variability in CO2 concentration. Three-dimensional hydrodynamic modeling demonstrated that diel differences in water temperature between plant mats and open water and basin-scale motions caused lateral exchanges of CO2 linking vegetated habitats to open water. Our findings extend understanding of CO2 in tropical lakes and floodplains with measurements and models that emphasize the importance of flooded forests and aquatic herbaceous plants fringing floodplain lakes as sources of carbon dioxide to the open waters. 

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4. Increased floodplain inundation in the Amazon since 1980

   https://doi.org/10.1088/1748-9326/acb9a7  

   Fleischmann, Ayan S.; Papa, Fabrice; Hamilton, Stephen K.; Fassoni-Andrade, Alice; Wongchuig, Sly; Espinoza, Jhan-Carlo; Paiva, Rodrigo C. D.; Melack, John M.; Fluet-Chouinard, Etienne; Castello, Leandro; et al (February 2023, Environmental Research Letters)

   Abstract Extensive floodplains throughout the Amazon basin support important ecosystem services and influence global water and carbon cycles. A recent change in the hydroclimatic regime of the region, with increased rainfall in the northern portions of the basin, has produced record-breaking high water levels on the Amazon River mainstem. Yet, the implications for the magnitude and duration of floodplain inundation across the basin remain unknown. Here we leverage state-of-the-art hydrological models, supported byin-situand remote sensing observations, to show that the maximum annual inundation extent along the central Amazon increased by 26% since 1980. We further reveal increased flood duration and greater connectivity among open water areas in multiple Amazon floodplain regions. These changes in the hydrological regime of the world’s largest river system have major implications for ecology and biogeochemistry, and require rapid adaptation by vulnerable populations living along Amazonian rivers. 

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5. Methane, Microbes and Models in Amazonian Floodplains: State of the Art and Perspectives

   https://doi.org/http://dx.doi.org/10.5772/intechopen.90247  

   Barros, D.J.; Bento, M.S.; Ferreira, M.S.; Carmo, J.B.; Toppa, R.H.; Neu, V.; Varesche, M.B.A.; Morais, P.B.; and Navarrete, A.A. (January 2019, Changing Ecosystems and Their Services)

   Amazon floodplain ecosystems include open water and intermittent flood forest and agricultural systems with different water types. They are a significant natural source of methane (CH4) in the tropics. When soils are flooded and become anoxic, CH4 is produced by methanogenesis, while microbially mediated aerobic and anaerobic oxidation of CH4 serves as the primary biological sink of this greenhouse gas. Measurements of rates and controls on CH4 production and emission in the Amazon basin mainly come from studies on individual wetlands and floodplain lakes. Similarly, microbial communities in those Amazon floodplain habitats have been studied on individual lakes based on sequence-specific DNA analysis. Existing biogeochemical ecosystem models of CH4 from the Amazon floodplains focus on soil properties or involve factors such as pH, redox potentials, or substrates. None of these models incorporate appropriate seasonal inundation; neither the microbiota does it as a component. In this sense, our chapter will highlight how the important efforts already contributed to understand the CH4 emission and its connections with abiotic and biotic factors in Amazon floodplains, as well as emphasize the need of encouraging cooperation and exchange of experience between research teams by using different approaches and scientific methods." 

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