Navegando por Assunto "Ecologia dos rios"

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Acesso aberto (Open Access)
Caracterização biogeoquímica de ecossistemas amazônicos: rios e lagos selecionados das microrregiões Bragantina, do Salgado e Guajarina - PA
(Universidade Federal do Pará, 1999) MENEZES, Lúcia Beckmann de Castro; LIMA, Waterloo Napoleão de; http://lattes.cnpq.br/1229104235556506
It was compared physical, chemical, physical-chemical and hydrobiological environmental parameters of waters and of aquatic humic material, in three kind of places seemingly identified, because these parameters are excellent indicators of biogeochemical and ecophysiological characteristics of aquatic ecosystems, in the attempt of characterizing the influence of the biogeochemical factors of pollution, the anthropogenic influence and the studied ecosystems productivity. It was collected samples in the course of the Guama river, in Ourem – Bragantina zone (high course), in Bujaru (medium course) and in Belem - Guajarina zone (close to estuary), as well as in two lakes of coastal plain located in the island of Atalaia (Salinopolis), and still in the Arapepo river (municipal district of Salinopolis – Salgado zone), this one under strong influence of the waters of the Atlantic ocean, in the months of December of 1996 (drought period), May of 1997 (rainy period) and October of 1997 (drought period). The methods used in the characterization involved physical-chemical analysis and chemical analysis for the determination of the chemical composition in relation to the dominant ions and the indicators of the presence and of the decomposition of the organic matter (humic material) and hydrobiological analysis, for chlorophyll evaluation, in natural waters, submitted or not to an anthropic action. It was utilized the ultraviolet and visible spectrophotometry and in the infra-red spectroscopy to the characterization of the natural organic matter, where the humic acid and fulvic acid prevail. The spectra in the ultraviolet-visible were also used for the identification of the chlorophyll. The analytic results have showed a clear difference among the studied ecosystems, suggesting an influence of an anthropic action in the Guama river, which characterizes the lakes in Salinopolis as an ambient with high amount of organic matter (humic substances) and the Arapepo river presenting results very differents due to the oceanic influence and to the occurrence of mangroves in its margins, being the only ecosystem where the occurrence of photosynthetics pigments were perceived (chlorophyll). The calculation of the ionic relation indicated the presence of marine intrusion in the environments of the lakes I and II, Arapepo river and Guama river (Belem). The seasonal was reflected intensively in the three studied ambients, through parameters as color, turbidity, specific conductivity, chloride, sulfate, organic matter (consumed oxygen), iron and the larger cations (calcium, magnesium, sodium and potassium), notedly in the physiografic area of the Salgado zone. The relation carbon/nitrogen observed for the humic substances suggests that the humic material of the lakes has an older formation than the rivers. The rate E4/E6 obtained through the spectra in the ultraviolet-visible indicates that the humic and fulvic acids present in the samples have a high aromaticity. The interpretation of the spectra of absorption in the area of the infra-red, has permitted to verify that there are present the most characteristic bands, indicating the presence of groups C-H, C=O and COOH and also of aromatic skeleton and suggesting the formation of humic substances - metal complex, what is in conformity with the analytic results obtained for metals in the humic material. The amount of metals (iron, manganese, copper, chromium and zinc) presents in the humic material were always larger in the samples of the Guama river (Belem), what suggests enrichment due to anthropogenic influence.
Acesso aberto (Open Access)
Dinâmica do carbono dissolvido no Rio Acre: variações espaciais e sazonais
(Universidade Federal do Pará, 2007) SOUSA, Eliete dos Santos; SALIMON, Cleber Ibraim; http://lattes.cnpq.br/4353834821288043; FIGUEIREDO, Ricardo de Oliveira; http://lattes.cnpq.br/2388049759708934
The main objective of this study was to study the dissolved carbon dynamics along a reach of the Acre River, evaluating the influence of Rio Branco city urban area and of the discharge from three of its tributaries (Riozinho do Rola, igarapé Judia and igarapé São Francisco), as well as the influence of hydrological seasonal changes. Samples were taken monthly, between December 2006 and September 2007, at five sites in Acre River and one site at the tributaries mouths. Each sample consisted of 1 liter of river/tributary water, which was submitted to filtering and aliquots withdrawn for dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and major ions (Ca2+, Mg2+, K+, Na+, NH4 +, HCO3 -, Cl-, SO4 2-, NO3 -, NO2 -, e PO4 3-) analysis. Electrical conductivity, pH, dissolved oxygen and water temperature measurements were also made. Mean annual pH in Acre River varied from 6.46 to 6.54 between sites and electrical conductivity presented mean values from 69.93 to 77.84 μS cm-1. In the tributaries, the mean annual pH ranged from 6.10 to 6.51 and electrical conductivity presented annual means from 54.08 and 153.03 μS cm-1. Na+ and Ca2+ were the dominant cations for both Acre River and its tributaries, while main anions were Cland SO4 2-. The mean annual DOC concentration in Acre River ranged from 4.62 to 5.17 mg l-1, with no significant difference among sampling sites. The tributaries’ mean annual DOC concentrations varied from 3.55 to 6.55 mg l-1. The concentrations were significantly higher in the high water period, with averages that ranged from 6.26 to 6.39 mg l-1 in Acre River sites. igarapé São Francisco was the only tributary that did not present differences between the seasons. Mean annual DIC concentration in Acre River ranged from 527.91 to 598.18 μM, with no significant difference among sampling sites. The higher concentrations were observed in the dry season, ranging from 816.31 to 998.52 μM. Mean annual DIC concentration in the tributaries ranged from 248.54 to 986.50 μM. Mean annual CO2 partial pressure (pCO2) in Acre River sites ranged from 3559 and 4059 ppm, with no significant differences among sites and with higher values in high waters. Based on these results, we conclude that the dissolved carbon dynamics in Acre River have not presented significant variations due to the tributaries discharge or due to the sewage discarded. On the other hand, hydrological seasonal changes are the most important drivers for changes in carbon dynamics.