IB01-56 POSTER

NET ECOSYSTEM METABOLISM AND NON-CONSERVATIVE FLUXES OF DISSOLVED NUTRIENTS IN A TROPICAL MANGROVE ESTUARY, PIAUí RIVER, NE BRAZIL.

M.F.L. SOUZA (Núcleo de Estudos Oceanográficos, DCET, UniversidadeEstadual de Santa Cruz, Rod. Ilhéus/Itabuna Km 16, Ilhéus, BA, 45.650-000,Brazil, marland@uol.com.br); V. R. Gomes (Departamento de EngenhariaQuímica, Universidade Federal de Sergipe, Campus Universitário, SãoCristóvão, SE, 49.100-000, Brazil, vivi@ufs.br); S. S. Freitas(Departamento de Engenharia Química, Universidade Federal de Sergipe,Campus Universitário, São Cristóvão, SE, 49.100-000, Brazil,simfreitas@ufs.br); R. C. B. Andrade (Programa de Pós-graduação emGeoquímica, Universidade Federal Fluminense, Outeiro de S.J. Batista, s/n,Niterói, RJ, 24.007-000, Brazil, regina@geoq.br); B. A. Knoppers(Departamento de Geoquímica, Universidade Federal Fluminense, Outeiro deS.J. Batista, s/n, Niterói, RJ, 24.007-000, Brazil, geoknop@geoq.uff.br)

The net ecosystem metabolism (NEM) and C, N and P mass balance were assessed for the Piauí River estuary in northeastern Brazil. Dissolved inorganic carbon (DIC) concentrations and fluxes were measured over a year along this mangrove-dominated estuary. The estuary served as a source of DIC to the atmosphere with an estimated flux of 13 moles CO2 . m-2 . yr-1.Input from the river was 46 moles CO2 . m-2 . yr-1. The metabolism of the system was heterotrophic, but short periods of autotrophy occurred in the lower more marine portions of the estuary. The pelagic system was more orles balanced between auto- and hetero trophy, whereas the benthic and inter tidal mangrove region was heterotrophic. Estimated annual NEM yielded a total DIC consumption that range from 12 - 36 moles CO2 . m-2 . yr-1. Two small reservoirs retain the fluvial inputs of POC and DIN, promoting are duction of C:N and C:P particulate ratios. A mass balance approach produced positive non-conservative fluxes of DIP, DIN and DIC, the later almost equivalent to the losses tothe atmosphere. The estuary acts as a source of these compounds through netnon-conservative fluxes. Mangrove forests and tidal mudflats were responsible for 54 - 95% of NEM and are the main sites of organic decomposition to sustain net heterotrophy. The main source for this organic matter is the anthropogenic inputs. The mangrove areas are the highest estuarine sources of DIP, DIC and DIN, the latter probably by N-fixation and re mineralization.