RESUMOA eutrofização e as emissões de gases do efeito estufa em ecossistemas aquáticos continentais são problemas estreitamente relacionados com a produção e emissão de nitrogênio (N) em muitas formas, especialmente as formas inorgânicas que tem sido fortemente aumentada pelo uso das bacias hidrográficas e do solo pelo homem. Quantidades de N amoniacal, como amônia inorgânica (NH 3 ) e amônio (NH 4 + ), são liberadas na decomposição orgânica e pode ter implicações ecológicas em áreas altamente produtivas e lagoas costeiras que recebem aportes autóctones terrestres e insumos orgânicos. O objetivo desse estudo foi avaliar as mudanças em curto prazo e a variabilidade intralagunar para as emissões de amônia a partir de uma lagoa costeira tropical urbana h -1 , ou seja, valores 50 vezes maiores do que os observados nas outras estações. Aumentos drásticos nas emissões de amônia foram relatados com eventos de precipitação, variando 700 vezes de 1.2-5 µg N m -2 h -1 antes da chuva para 3500 µg N m-2 h -1 nos dias chuvosos. As emissões de amônia em águas superficiais de lagoas costeiras tropicais urbanas podem ser altamente dinâmicas, mostrando drásticas mudanças de curto prazo e heterogeneidade intralagunar alta, com implicações importantes para as emissões de N a partir de extensas áreas inundadas para a atmosfera. Palavras-chave: nitrogênio; mudanças de curto prazo; heterogeneidade intralagunar; emissão de amônia; lagoas costeiras tropicais. ABSTRACT DRASTIC SHORT-TERM CHANGES AND INTRA-LAKE HETEROGENEITY IN AMMONIUM EMISSIONS FROM A TROPICAL URBAN COASTAL LAGOON (RODRIGO DE FREITAS, RIO DE JANEIRO) TO THE ATMOSPHERE.Eutrophication and emissions of greenhouse gases in continental aquatic ecosystems are a problem closely related to production and emission of nitrogen (N) in many forms, especially those inorganic that have been strongly increased by the human land use in the watershed. Ammoniacal N amounts, as inorganic ammonia (NH 3 ) and ammonium (NH 4 + ), are released by the organic decomposition and may have important ecological implications in highly organic and productive coastal lagoons receiving terrestrial or autochthonous organic inputs . The aim of this study was to assess short-term ckanges and the intralake herterogeneity for ammonia emissions from a tropical coastal urban lagoon (Rodrigo de Freitas) to the atmophere. ammonia fluxes varied intensely from 1.2 to 3500µg N m -2 h -1 among sampling stations and over the daytime The most eutrophic station (next to the racetrack of Rio de Janeiro), the also showed higher values
Methane (CH4) oxidation is a critical process to reduce CH4 emissions from aquatic environments to the atmosphere. Considering the continuous increase in nitrogen in rivers, lakes, and lagoons from human sources, we re-evaluated the still controversial potential effect of inorganic nitrogen on CH4 oxidation. Here, we approached three shallow coastal lagoons that represent great environmental heterogeneity and used slurry sediments as a model system. The addition of ammonium chloride (NH4Cl) and potassium nitrate (KNO3) significantly stimulated CH4 oxidation in the sediments of all studied lagoons, indicating the potential limitation of nitrogen for the growth of CH4 oxidizing bacteria. Our findings contrast to some previous reports, where ammonium and nitrate inhibited CH4 oxidation in sediments. Indeed, our experiment was performed in a more realistic range in relation to natural concentrations of inorganic nitrogen in aquatic systems (0.5 to 1 mM) and was opposed to extreme concentrations previously used (2 to 50 mM). Our results point to the need to further assess the connection between nitrogen inputs and CH4 budgets in aquatic sediments, considering the potential fuel for CH4 oxidation that may affect the global greenhouse gas balance
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