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Other Titles: Phosphorus dynamic ina a transect of mangrove sediments
Keywords: Fósforo (Ph);  manguezal;  degradação;  contaminação ambiental.;  phosphorus (Ph);  mangrove;  degradation;  environmental contasmination
Issue Date: 1-Mar-2006
Abstract: Sediment and vegetation of mangrove forest can influence the environmental quality of areas affected by urban sewage due to retention or incorporation of contaminants such as phosphorus. Considering the importance of the mangroves and dynamics of the phosphorus for this ecosystem, this work characterizes the organic and the inorganic fractions of phosphorus in sediments of the Mauá mangrove forest (Guanabara Bay). For this study, seven sediment core were collected (1) in the mud flat without presence of mangrove trees (core PL), (2) in areas with vegetation degraded probably by deforestation (cores MD1 and MD2), (3) in areas with dead vegetation probably by insect attacks (core MP), (4) where the mangrove forest has senescent trees (core MS), (5) in an area with vegetation is apparently healthy (core MV1 and MV2). The results showed that the average values of inorganic phosphorus (IP) in the sediment decrease in the continent direction. This variation can be explained by the incorporation of IP by mangrove vegetation also preserved in this direction. Core MD1 and MD2 showed higher values of IP. This result may be explained by a presence of oxidized sediments (with brown color), since oxidized sediments tend to sequester phosphorus. The increase of IP in cores PL, MD1, MD2, MP and MS from bottom to surface problably is due to an increase of urban effluent input since 1950 (210Pb data), in agreement with the increase of the Rio de Janeiro urban population. The average values of organic phosphorus (OP) and organic matter (OM) in the sediment increases in the continental direction. These results can be explained by the preservation of the forest in the cores next to the continent. The %PO in core PL is 16% and this core showed a strong negative correlation of OM with OP. Cores MD1 and MD2 presented a %OP of 6% and 17%, respectively. These cores presented weak correlation of OM with OP. In core MP the %OP is equal to 55% and this core showed weak correlation of OM with OP. These results show that OM and OP have different origins. In core MS, the %OP is 70% and the OP has strong positive correlation with the OM. Cores MV1 and MV2 have %OP of 90 and 86%, respectively. In these cores the OP showed strong positive correlation with OM. The comparison with other studies in Guanabara Bay showed that TP concentrations of core PL closer to those within the bay area, evidencing a context of phosphorus contamination in this environment. The results evidence the importance of mangrove vegetation on phosphorus distribution and geochemical fractionation in sediments.
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