Marcelo Bernardes

Amazon River carbon dioxide outgassing fuelled by wetlands

River systems connect the terrestrial biosphere, the atmosphere and the ocean in the global carbon cycle. A recent estimate suggests that up to 3 petagrams of carbon per year could be emitted as carbon dioxide (CO2) from global inland waters, offsetting the carbon uptake by terrestrial ecosystems. It is generally assumed that inland waters emit carbon that has been previously fixed upstream by land plant photosynthesis, then transferred to soils, and subsequently transported downstream in run-off. But at the scale of entire drainage basins, the lateral carbon fluxes carried by small rivers upstream do not account for all of the CO2 emitted from inundated areas downstream. Three-quarters of the world’s flooded land consists of temporary wetlands, but the contribution of these productive ecosystems to the inland water carbon budget has been largely overlooked. Here we show that wetlands pump large amounts of atmospheric CO2 into river waters in the floodplains of the central Amazon. Flooded forests and floating vegetation export large amounts of carbon to river waters and the dissolved CO2 can be transported dozens to hundreds of kilometres downstream before being emitted. We estimate that Amazonian wetlands export half of their gross primary production to river waters as dissolved CO2 and organic carbon, compared with only a few per cent of gross primary production exported in upland (not flooded) ecosystems. Moreover, we suggest that wetland carbon export is potentially large enough to account for at least the 0.21 petagrams of carbon emitted per year as CO2 from the central Amazon River and its floodplains. Global carbon budgets should explicitly address temporary or vegetated flooded areas, because these ecosystems combine high aerial primary production with large, fast carbon export, potentially supporting a substantial fraction of CO2 evasion from inland waters.

Particulate Organic Matter Distribution along the Lower Amazon River: Addressing Aquatic Ecology Concepts Using Fatty Acids

One of the greatest challenges in understanding the Amazon basin functioning is to ascertain the role played by floodplains in the organic matter (OM) cycle, crucial for a large spectrum of ecological mechanisms. Fatty acids (FAs) were combined with environmental descriptors and analyzed through multivariate and spatial tools (asymmetric eigenvector maps, AEM and principal coordinates of neighbor matrices, PCNM). This challenge allowed investigating the distribution of suspended particulate organic matter (SPOM), in order to trace its seasonal origin and quality, along a 800 km section of the Amazon river-floodplain system. Statistical analysis confirmed that large amounts of saturated FAs (15:0, 18:0, 24:0, 25:0 and 26:0), an indication of refractory OM, were concomitantly recorded with high pCO2 in rivers, during the high water season (HW). Contrastingly, FAs marker which may be attributed in this ecosystem to aquatic plants (18:2ω6 and 18:3ω3) and cyanobacteria (16:1ω7), were correlated with higher O2, chlorophyll a and pheopigments in floodplains, due to a high primary production during low waters (LW). Decreasing concentrations of unsaturated FAs, that characterize labile OM, were recorded during HW, from upstream to downstream. Furthermore, using PCNM and AEM spatial methods, FAs compositions of SPOM displayed an upstream-downstream gradient during HW, which was attributed to OM retention and the extent of flooded forest in floodplains. Discrimination of OM quality between the Amazon River and floodplains corroborate higher autotrophic production in the latter and transfer of OM to rivers at LW season. Together, these gradients demonstrate the validity of FAs as predictors of spatial and temporal changes in OM quality. These spatial and temporal trends are explained by 1) downstream change in landscape morphology as predicted by the River Continuum Concept; 2) enhanced primary production during LW when the water level decreased and its residence time increased as predicted by the Flood Pulse Concept.

Geochemical Characteristics Related to the Gregite-Producing Multicellular Magnetotactic Prokaryote Candidatus Magnetoglobus multicellularis in a Hypersaline Lagoon

We studied the geochemical properties of sediment layers where the gregite-producing multicellular magnetotactic prokaryote Candidatus Magnetoglobus multicellularis exists. The ratio of iron and bioavailable sulfur concentrations regulates the population density of this microorganism. The population density can reach 8.5 × 102 cells/cm3 at an iron to sulfur ratio of 0.5. In iron- and sulfur-rich environments, microorganisms concentrated in the upper region of the oxic-anoxic zone, following an increasing nitrogen gradient with a lower isotopic 15N/14N ratio. Candidatus Magnetoglobus multicellularis prefers environmental conditions that favor the biomineralization of greigite, but in situations where the nutrient availability is low, it moves to more suitable sites.

Uso dos fenóis da lignina no estudo da matéria orgânica na Várzea do Lago Grande Curuái, Pará e no Lago do Caçó, Maranhão, Brasil

Este estudo tem por objetivo caracterizar os sedimentos superficiais, quanto ao seu teor e qualidade dos fenois da lignina, em dois sistemas lacustres distintos: a Varzea do Lago Grande Curuai (PA) e o Lago do Caco (MA). A Varzea do Lago Grande Curuai e localizada na margem direita do Rio Amazonas, aproximadamente 850 km da foz e e caracterizada pela presenca de lagos de aguas brancas e pretas. O Lago do Caco esta localizado no Maranhao, na borda do ecossistema amazonico. Foram realizadas analises da concentracao de lignina (λ), carbono orgânico total (COT), nitrogenio e isotopos do carbono (δ13C). Os resultados indicam que os sedimentos superficias de lagos de aguas brancas apresentam baixos valores de COT (1,5 a 3,6%), baixa concentracao de λ (0,73 a 1,28 mg.100mg CO-1) e alto indice de degradacao (0,29 a 2,01). Os sedimentos superficiais de lagos de aguas pretas apresentam maiores valores de COT (6,0 a 12,1%) e de λ (1,44 a 1,93 mg.100mg CO-1) em relacao aos sedimentos de lagos de aguas brancas, porem baixos em comparacao com os sedimentos do Lago do Caco (7,2 ~ 15,3% e 1,83 ~ 4,64 mg .100mg CO-1, respectivamente). Atraves das analises realizadas foi possivel identificar diferentes contribuicoes de fontes assim como diferentes estados de preservacao da materia orgânica sedimentada nos dois sistemas apresentados.

Environmental Processes, Biodiversity and Changes in Admiralty Bay, King George Island, Antarctica

The isolation of Antarctica from South America during the Oligocene (~35 mya) formed the Southern Ocean, generated the northward flow of the Atlantic Antarctic Bottom Water, and numerous unique geological and oceanic processes (e.g. an active spreading centre in the Bransfield Strait, ridge trench collision, gas hydrates on modern sediments, and complex circulation) along the northern end of the Antarctic Peninsula in particular (Barker and Burrell 1982; Pearse et al. 2001; Barker and Thomas 2004; Thomson 2004; Turner et al. 2009).

Benthic influence on the metabolism of a shallow tropical lagoon (Lagoa da Barra, Brazil)

Pelagic and benthic carbon metabolism in the shallow tropical Barra Lagoon was studied weekly between 1990 and 1993, in periods characterized by temporary nitrogen limitation, fish kills and transitory colonization of the bottom by macro-algae. Diurnal and nocturnal metabolic rates were measured by monitoring changes in CO2 content in entire water columns (free water and waters incubated in plexiglass tubes with and without inclusion of sediment). Total community carbon metabolism exhibited a marked autotrophism and high short term changes, dampening seasonal trends. Autotrophism and heterotrophism of the lagoon were controlled by phytoplankton biomass variations. In the presence of sediment, diurnal net benthic production was 11 to 64% of total diurnal net production, and nocturnal net benthic mineralization was 21 to 52% of total nocturnal net mineralization. The imbrication between the pelagic and benthic organic carbon cycles regulated carbon metabolism of the total community. A severe temporary nitrogen limitation, a fish kill and a temporary shift in primary producers did not substantially change metabolic rates because appropriate shifts occurred from the pelagic carbon cycle to the benthic carbon cycle, and vice-versa.

Hydrological pulse regulating the bacterial heterotrophic metabolism between Amazonian mainstems and floodplain lakes

We evaluated in situ rates of bacterial carbon processing in Amazonian floodplain lakes and mainstems, during both high water (HW) and low water (LW) phases (p < 0.05). Our results showed that bacterial production (BP) was lower and more variable than bacterial respiration, determined as total respiration. Bacterial carbon demand was mostly accounted by BR and presented the same pattern that BR in both water phases. Bacterial growth efficiency (BGE) showed a wide range (0.2–23%) and low mean value of 3 and 6%, (in HW and LW, respectively) suggesting that dissolved organic carbon was mostly allocated to catabolic metabolism. However, BGE was regulated by BP in LW phase. Consequently, changes in BGE showed the same pattern that BP. In addition, the hydrological pulse effects on mainstems and floodplains lakes connectivity were found for BP and BGE in LW. Multiple correlation analyses revealed that indexes of organic matter (OM) quality (chlorophyll-a, N stable isotopes and C/N ratios) were the strongest seasonal drivers of bacterial carbon metabolism. Our work indicated that: (i) the bacterial metabolism was mostly driven by respiration in Amazonian aquatic ecosystems resulting in low BGE in either high or LW phase; (ii) the hydrological pulse regulated the bacterial heterotrophic metabolism between Amazonian mainstems and floodplain lakes mostly driven by OM quality.

Carbon accumulation rates recorded in the last 150 years in tropical high mountain peatlands of the Atlantic Rainforest, SE - Brazil

Peatlands are environmental matrices that store large amounts of organic carbon (TOC) and work as records of environmental changes. Recent record of organic carbon accumulated were assessed in two Forest National Parks, Itatiaia and Serra dos Órgãos in the Southeastern of Brazil. Based on organic and inorganic characterization, the cores from peatlands presented a predominance of organic material in an advanced stage of decomposition and those soils were classified as typical Haplosaprists Histosols. The combination of favorable topographic and climatic conditions led to rapid C accumulation across coastal mountain in the tropical peatlands studied, presenting an average accumulation rate of C, in the last century, of 194gCm-2yr-1 about 7 higher times than the rate found in boreal and subarctic peatlands, those higher values may be related to changes in the hydrological cycle occurred since 1950s.