The aim of this study was to evaluate methane concentration in water column and pore water at limnetic and littoral regions of a coastal lagoon. At the littoral region samples were taken from three monospecific macrophytes stands (Typha domingensis, Eleocharis interstincta and Potamogeton stenostachys). The methane concentration in the pore water at the littoral region was higher than the concentration found at the limnetic region in each fraction
| Estudos 704Marinho, Fonseca e Esteves / Impactos antrópicos nas lagoas costeiras do norte do estado do Rio de Janeiro: uma revisão sobre a eutrofização artificial e gases de efeito estufa a incorporação ou a emissão de carbono para a atmosfera, na forma de gases de efeito estufa (CO 2 e CH 4 ). Neste artigo, avalia-se a contribuição de diversos estudos para a compreensão da relação entre a eutrofização artificial e a dinâmica do CO 2 e do CH 4 em lagoas costeiras. Alguns dos fatores controladores da dinâmica dos gases de efeito estufa foram identificados. De modo geral, observou-se que a eutrofização artificial potencializa a emissão de CO 2 e de CH 4 para a atmosfera. Os estudos foram conduzidos de forma segmentada ao invés de uma abordagem integrada sobre os principais fatores controladores. Os estudos foram realizados em diferentes programas de pós-graduação no estado do Rio de Janeiro. Destaca-se a importância desses programas, uma vez que os profissionais formados continuam desenvolvendo pesquisas em diversas instituições pelo Brasil.Palavras-chave: Lagoas Costeiras. Eutrofização Artificial. Aquecimento Global. Pós-Graduação. Metano. Dióxido de Carbono.
AbstractArtificial eutrophication is an anthropic action that alters the metabolism of freshwater ecosystems, increasing carbon incorporation from or emission into the atmosphere in the form of greenhouse gases (CO 2 and CH 4 ). In this paper, we evaluated the contribution of several studies for the understanding of the relationship between the artificial eutrophication and the dynamics of CO 2 and CH 4 in coastal lagoons. Some controlling factors of the dynamics of greenhouse gases were identified. In general, it was observed that artificial eutrophication enhances the emission of CO 2 and CH 4 into the atmosphere. The studies were conducted in a segmented rather than on an integrated approach to the main controlling factors. The studies were conducted in different graduate programs in the State of Rio de Janeiro. We highlight the importance of such graduate programs, since graduated professionals continue to develop research in various institutions in Brazil.
Aquatic macrophytes usually show high productivity rate, especially in shallow environments, and may constitute the main source of organic matter to these ecosystems. The coastal lagoons are shallow environments that typically present a broad colonization by aquatic macrophytes. The organic matter derived from aquatic macrophytes consists of detritus and root exudates, from live plants. Methanogens are microorganisms that use labile organic matter (e.g. acetate) in the metabolism, releasing methane (CH4) as an end product. Assessing the influence of aquatic macrophytes on methanogenesis is fundamental to understanding the carbon cycle in shallow environments, such as coastal lagoons. A peculiarity of coastal lagoons that may also influence the methanogenesis is its proximity to the sea, providing the entrance of sulfate in the environment. The methanogenesis can be inhibited by the sulfate reduction when there is sulfate availability sulfate. In this context, we aimed to analyze the methane production in an aquatic macrophyte stand and in the limnetic region of a coastal lagoon, assessing the influence of quantity and quality of organic carbon and sulfate availability on methane production in the sediment profile. We observe that the presence of aquatic macrophytes benefits the methanogenesis, not only by detritus accumulation, but particularly by the release of root exudates from the living plants. The variation in quantity and quality of organic carbon is the main factor that controls the range and shape of the methane production curves. The availability of sulfate presents probably a secondary role, being im-* Corresponding author.A. L. dos Santos Fonseca et al. 1676 portant when the organic matter is not sufficient for the occurrence of methanogenesis and sulfate reduction simultaneously.
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