Elevadas mudanças de curto prazo e heterogeneidade intralagunar na emissão de amônia de uma lagoa costeira urbana tropical (lagoa Rodrigo de Freitas - Rio de Janeiro) à atmosfera

Abstract

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 (NH3) and ammonium (NH4+), 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-2h-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 of ammonia evasion, in average (± standard error), 1052±188.6μg N m-2h-1, or about 50 times higher than those observed in other stations. Drastic increases in ammonia emissions were reported with rainfall events, varying 700 times from 1.2-5μg N m-2h-1 before to 3500μg N m-2h-1 in rainy days. Ammonia in surface waters of urban tropical coastal lagoons may be highly dynamic, showing drastic short-term changes and high intralake heterogeneity with important implications for N emissions from extensive flooded areas to the atmosphere.