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Title: Processos Microbiológicos e composição da matéria orgânica relacionados à eutrofização de uma lagoa costeira hipersalina, L. Araruama, RJ.
Keywords: Biopolímeros;  Esteróis;  Isótopos;  Atividade bacteriana;  Biomarcadores;  Biopolymers;  Sterols;  Isotopes;  Bacterial activity;  Biomarkers
Issue Date: 18-Feb-2008
Abstract: The hypersaline lagoon of Araruama - RJ is suffering, in the last decades, disordered occupation of its drainage basin and consequent contribution of M.O. originating from domestic sewage, altering drastically your trophic characteristics, from oligo to hypertrophic. The present work intends to evaluate the organic matter composition and the microbial processes in the Araruama Lagoon (RJ) and to relate to the current hypertrophic conditions. Thus, different events were considered, such as rainy, dry and tide (low and high) periods. The sites for water column and sediment sampling were selected to characterize the fluvial contribution in Araruama station (AR), the intern cycling - São Pedro da Aldeia station (SP) and the exchanges with the ocean - Cabo Frio station (CF). The high primary production found (chlorophyll: 450μg.L-1) and the reduced concentrations of the nitrogen forms in the water column (NO2, NO3 and NH4) indicate phytoplankton consumption. High concentrations of dissolved organic carbon were observed (average of 17.5mgC.L-1), resulting in a high respiratory rate (average of 2.08μMO2.L-1.h-1). The biopolymer concentrations were high in the sediment, mostly lipids and carbohydrates (2.9 and 2.57mg.g-1, respectively), presenting the relationship lipids>carbohydrates>proteins, which differs from what is described by the literature for the Northern Hemisphere. The organic carbon stocked in the lagoon s sediments presented medium values of 5,5%, 10,4 for C/N and -14.8 and 6.21 for δ13C and δ15N, respectively. Generally, those results indicate a mixture of sources for the deposited carbon in the sediments. The relative proportion among the researched sterols demonstrated a predominance of stigmasterol in most of the samples, probably coming from phytoplankton. Despite of this compound are commonly related to vascular plants the absence of a high amount of rivers in the drainage basin turn this source without importance. Coprostanol was present in high concentrations at AR station (average of 263μg.g-1), but it was also found in small scale at Cabo Frio and less at São Pedro, and it seems to be a better sewage indicator at the hypersaline environment than the termotolerant coliforms. The bacterial biomass and activities in the sediment (metabolic and enzymatic) were high, evidencing the intense cycling of organic matter in this compartment and indicating that the lagoon can return to better conditions in short or medium period, if effective programs for its recovery are adopted.
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