OS FATORES REGULADORES DO METABOLISMO AQUÁTICO E SUA INFLUÊNCIA SOBRE O FLUXO DE DIÓXIDO DE CARBONO ENTRE OS LAGOS E A ATMOSFERA

Carbon dioxide (CO2) emissions to atmosphere increase the global warming. Lake-atmosphere CO2 fluxes are mainly determined by balance between CO2 fixation from primary production and CO2 evasion from respiration (named aquatic metabolism). Lakes may show a net CO2 sink from atmosphere (autotrophic metabolism) or a net CO2 evasion to atmosphere (heterotrophic metabolism). However, global lakes are considered a relevant CO2 source to atmosphere, driven by high terrestrial organic inputs. The aim of this review was to discuss the main bottom-up and top-down controls on aquatic metabolism and them role on air-lake CO2 fluxes. We concluded that scientific literature about regulators factors on CO2 concentrations in lakes shows a strong lack of integrated approaches between central and marginal areas in intra-lake scale, as well of studies with tropical lakes in global scale.  As emissões de dióxido de carbono (CO2) à atmosfera intensificam o aquecimento global. Os fluxos de CO2 entre os lagos e a atmosfera são principalmente determinados pelo balanço entre a fixação de CO2 pela produção primária e a liberação de CO2 pela respiração (denominado metabolismo aquático). Lagos podem apresentar em relação à atmosfera apreensão líquida de CO2 (metabolismo autotrófico) ou liberação líquida desse gás (metabolismo heterotrófico). No entanto, os lagos são considerados relevantes fontes de liberação de CO2 para atmosfera em escala global. O objetivo desta revisão foi discutir os principais fatores reguladores ascendentes e descendentes do metabolismo aquático e o seu papel no fluxo de CO2 entre lagos e a atmosfera. Nós concluímos que a literatura científica sobre os fatores reguladores das concentrações de CO2 em lagos apresenta uma grande carência de abordagens integradas entre as áreas central e marginal na escala intralagunar, bem como de estudos com lagos tropicais na escala global

A “metodologia da problematização” como alternativa no ensino na graduação: o problema enquanto solução

This paper discusses the Problem Based Learning Methodology as a teaching-learning strategy for environmental contents in Geography, focusing Engineering courses. We showed a novel pedagogical practice performed at the Fluminense Federal University (Niterói, Rio de Janeiro State) in order to bring reality closer and to stimulate autonomy in the professional formation from using scientific literature within the Problem Based Learning Methodology. The results indicated a development in the capacity for argumentation, contributing to a more critical, deep and grounded analysis construction. The proposed activity may represent a significant gain to the construction of knowledge for environmental issues in applied exact sciences, supporting the inherent interdisciplinary field of Geography.Este artigo apresenta a Metodologia da Problematização como estratégia de ensino utilizada nas disciplinas de Ecologia, ministrada para os cursos de Engenharia da Universidade Federal Fluminense no Rio de Janeiro. Com o intuito de aproximar a realidade e estimular a autonomia na formação de futuros profissionais, utilizaram-se artigos científicos de excelência em conjunto com a Metodologia da Problematização. Os resultados indicaram um desenvolvimento na capacidade de argumentação baseada em referências oficiais, contribuindo para uma construção de análise mais crítica, profunda e embasada. Além disso, possibilitou um ganho significativo na abrangência de temas socioambientais com enfoque transdisciplinar

O PAPEL DAS MACRÓFITAS AQUÁTICAS EMERSAS NOCICLODOFÓSFORO EMLAGOS RASOS

The phosphorus cycle is one of the biogeochemical cycles that has been more altered in the last decades due to strong antropic activity, being domestic sewage the main responsible in this process. The discussion of the emergent macrophytes role as mediators of a net transport of phosphorus from sediment to the water column (‘Phosphorus pump') or as net sinks of phosphorus becomes relevant for the phosphorus cycle understanding in aquatic ecosystems. The aim of this review is to discuss the main responsible mechanisms for phosphorus transference in emergent macrophytes and its consequences to the phosphorus cycle in shallow lakes.  O ciclo do fósforo é um dos ciclos biogeoquímicos que mais sofreu alterações nas últimas décadas devido a forte ação antrópica, sendo os efluentes domésticos os principais responsáveis neste processo. A discussão do papel das macrófitas emersas como mediadoras de um transporte líquido de fósforo do sedimento para a coluna d'água (‘Bomba de fósforo') ou como um sumidouro deste elemento torna-se relevante para o entendimento do ciclo fósforo em ecossistemas aquáticos. O objetivo principal desta revisão é discutir os principais mecanismos responsáveis pela transferência de fósforo em macrófitas emersas e suas conseqüências para o ciclo do fósforo em lagos rasos.

Inter- and intra-annual variations of pCO2 and pO2 in a freshwater subtropical coastal lake

Inland waters emit significant amounts of carbon dioxide to the atmosphere, but tropical and subtropical lakes are underrepresented in current assessments. Here we present results of a 6-year study of the dynamics of surface partial pressures of carbon dioxide and oxygen (pCO2 and pO2) in a subtropical lake, Lake Peri, Brazil, to determine how temperature, rainfall, and wind moderate surface concentrations. Both pCO2 and pO2 tended to increase during the transitions between seasons when rainfall increased, with pCO2 averaging 2.5–3-fold higher than atmospheric values. Occasionally during autumn/winter, pCO2 similarly increased and pO2 decreased. We infer that the increases in both gases during the transition periods resulted from increasing inputs of allochthonous material into the lake. Those in winter resulted from near-bottom intrusions that intermittently reach the depth of measurement. In autumn/winter, pCO2 was 3-fold higher (average 1700 µatm) compared to spring/summer (550 µatm), whereas changes in pO2 did not have a clear seasonal pattern. Overall median net CO2 evasion was 11 mg C m-2 d-1. Variability in the extent of rainfall and the associated high intra- and inter-annual variability in CO2 and CO2 emissions are in part controlled by atmospheric processes related to the South American Monsoon System and to El Niño Southern Oscillation cycles

Structure and function of methanogenic microbial communities in temporarily inundated soils of the Amazon rainforest (Cunia Reserve, Rondonia).

The floodplain of the Amazon River is a large source for the greenhouse gas methane, but the soil microbial communities and processes involved are little known. We studied the structure and function of the methanogenic microbial communities in soils across different inundation regimes in the Cunia Reserve, encompassing nonflooded forest soil (dry forest), occasionally flooded Igapo soils (dry Igapo), long time flooded Igapo soils (wet Igapo) and sediments from Igarape streams (Igarape). We also investigated a Transect (four sites) from the water shoreline into the dry forest. The potential and resilience of the CH4 production process were studied in the original soil samples upon anaerobic incubation and again after artificial desiccation and rewetting. Bacterial and archaeal 16S rRNA genes and methanogenic mcrA were always present in the soils, except in dry forest soils where mcrA increased only upon anaerobic incubation. NMDS analysis showed a clear effect of desiccation and rewetting treatments on both bacterial and archaeal communities. However, the effects of the different sites were less pronounced, with the exception of Igarape. After anaerobic incubation, methanogenic taxa became more abundant among the Archaea, while there was only little change among the Bacteria. Contribution of hydrogenotrophic methanogenesis was usually around 40%. After desiccation and rewetting, we found that Firmicutes, Methanocellales and Methanosarcinaceae became the dominant taxa, but rates and pathways of CH4 production stayed similar. Such change was also observed in soils from the Transects. The results indicate that microbial community structures of Amazonian soils will in general be strongly affected by flooding and drainage events, while differences between specific field sites will be comparatively minor.Funding Agencies|CNPq; CAPES; FAPERJ; Alexander von Humboldt Foundation; STINT Sweden [2012-2085]; Swedish Research Council [2012-00048]; ERC METLAKE [2017-2021]</p

Construção Coletiva de Material Paradidático Escolar sobre Mudanças Globais

Resumo Evidências crescentes têm sustentado a importância das mudanças globais no espaço geográfico, (i.e., aquelas alterações antropogênicas de escalas desde local a global que afetam a biosfera enquanto um sistema), indicando que uma compreensão coletiva sobre temáticas ambientais é essencial para tomada decisão e formulação de políticas para reduzir as desigualdades sociais. A relação entre as consequências das mudanças ambientais aos diferentes sujeitos sociais e as práticas socioespaciais de estudantes tem se tornado um tópico-chave para melhorar o processo ensino-aprendizagem. Apesar de sua relevância para educação em múltiplos níveis, a fronteira do conhecimento é comumente restrita a periódicos científicos especializados, não acessíveis em livros-texto tradicionais ao menos por longos períodos. No sentido de aproximar o conhecimento científico atual aos estudantes da escola, o desenvolvimento de linguagens atrativas incluindo recursos visuais e textuais em materiais didáticos complementares (paradidáticos) ainda é necessário, especialmente no dinâmico campo geográfico das mudanças globais, no qual novos conteúdos estão constantemente emergindo. Nesse artigo, o objetivo foi descrever o primeiro capítulo de material paradidático do projeto de extensão “Autoria Coletiva Universidade-Escola: Aproximando a Fronteira do Conhecimento sobre Mudanças Globais às Práticas Educativas”, baseado nas experiências de 2012 a 2018 durante a disciplina “Práticas Educativas IV”, oferecida pelo Departamento de Geografia da Universidade Federal Fluminense. A metodologia proposta pretende estimular a interação entre estudantes e professores de universidades e escolas para produzir materiais paradidáticos sobre informações científicas atuais (i.e., relacionadas a recentes descobertas publicadas em artigos de prestigiosos periódicos acadêmicos), as quais ainda não estão descritas nos livros didáticos tradicionais mas poderiam subsidiar relevantes discussões críticas contemporâneas em disciplinas do ensino médio. A primeira versão de cada material é preparada pelos graduandos para posterior contribuição de estudantes de nível médio e graduados sob a supervisão de professores e pesquisadores em pós-doutorado, revelando que a construção de conhecimento na universidade poderia ser associada à produção de instrumentos de ensino no ambiente escolar. Como conclusão, este projeto de extensão baseado na interação colaborativa entre universidade e escola poderia facilitar o processo ensino-aprendizagem na ciência das mudanças globais em ambos os níveis educacionais, uma prática potencialmente inovadora para formar sujeitos críticos em relação aos impactos ambientais em curso. Palavras-chave: Material Paradidático, Ensino Geográfico, Mudanças Globais &nbsp;&nbsp;&nbsp;&nbsp; Abstract Growing evidence has supported&nbsp;the importance&nbsp;of global change&nbsp;in the geographical space&nbsp;(i.e.,&nbsp;those human-induced alterations from local to global scales that affect the biosphere as a system), indicating that a collective understanding about environmental issues is essential for decision-making and policy implementation to reduce social inequalities. The relationship between the consequences of environmental changes to different social subjects and the environmental practices of students has become a key topic to improve the teaching-learning process.&nbsp;Despite its relevance for education at multiple levels, the threshold of knowledge is commonly restricted to specialized scientific journals, not accessible in traditional textbooks at least for long periods. In order to bring current scientific knowledge closer to school students, the development of attractive languages including textual and visual resources in complementary didactic (paradidactic) materials&nbsp;is still needed, especially in the dynamic geographical field of global change, in which new contents are constantly emerging. Here, the aim was to report the first chapter of paradidactic material&nbsp;of the outreach program " School-University Collective Authorship:&nbsp;Closing the Threshold of Knowledge about Global Change to Educational Practices”, based on experiences from 2012 to 2018 during the course "Educational Practices IV", offered by the Department of Geography at the Fluminense Federal University. The proposed methodology intends to stimulate the interaction among students and teachers from universities and schools to produce paradidactic materials on current scientific information (i.e., related to recent findings published in papers of prestigious academic journals), which are not still reported in traditional textbooks but could support important contemporaneous critical discussions in high school courses. The first version of each material is prepared by undergraduate students for further contribution of graduate and secondary students under the supervision of teachers and postdoctoral researchers, revealing that the construction of knowledge in the university could be associated with the production of teaching tools in the school environment. As a conclusion, this outreach program based on the collaborative interaction between university and school could facilitate the teaching-learning process on global change science at both educational levels, a potentially innovative practice to form critical subjects in relation to ongoing environmental impacts Key words: Paradidactic Material, School Geography, Global Chang

Large emissions from floodplain trees close the Amazon methane budget

Wetlands are the largest global source of atmospheric methane (CH4), a potent greenhouse gas. However, methane emission inventories from the Amazon floodplain, the largest natural geographic source of CH4 in the tropics, consistently underestimate the atmospheric burden of CH4 determined via remote sensing and inversion modelling, pointing to a major gap in our understanding of the contribution of these ecosystems to CH4 emissions. Here we report CH4 fluxes from the stems of 2,357 individual Amazonian floodplain trees from 13 locations across the central Amazon basin. We find that escape of soil gas through wetland trees is the dominant source of regional CH4 emissions. Methane fluxes from Amazon tree stems were up to 200 times larger than emissions reported for temperate wet forests6 and tropical peat swamp forests, representing the largest non-ebullitive wetland fluxes observed. Emissions from trees had an average stable carbon isotope value (δ13C) of −66.2 ± 6.4 per mil, consistent with a soil biogenic origin. We estimate that floodplain trees emit 15.1 ± 1.8 to 21.2 ± 2.5 teragrams of CH4 a year, in addition to the 20.5 ± 5.3 teragrams a year emitted regionally from other sources. Furthermore, we provide a ‘top-down’ regional estimate of CH4 emissions of 42.7 ± 5.6 teragrams of CH4 a year for the Amazon basin, based on regular vertical lower-troposphere CH4 profiles covering the period 2010–2013. We find close agreement between our ‘top-down’ and combined ‘bottom-up’ estimates, indicating that large CH4 emissions from trees adapted to permanent or seasonal inundation can account for the emission source that is required to close the Amazon CH4 budget. Our findings demonstrate the importance of tree stem surfaces in mediating approximately half of all wetland CH4 emissions in the Amazon floodplain, a region that represents up to one-third of the global wetland CH4 source when trees are combined with other emission sources