Caracterização da matéria orgânica de rios da Amazônia: black carbon, substâncias húmicas e labilidade
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2019-06-07
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Universidade Estadual Paulista (Unesp)
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O bioma Amazônico é mundialmente conhecido pela sua importância nos ciclos climáticos, biodiversidade e extensão. A área explorada nesse estudo compreendeu a região dos munícipios de Itacoatiara, Maués e Manaus, situados no estado do Amazonas, sendo esses dois primeiros pouco explorados. Sabe-se da importância da matéria orgânica natural (MON) na dinâmica de outras espécies, sendo essa formada por estruturas definidas ou indefinidas, com diferentes graus de labilidade frente a outras espécies, processos fotoquímicos e microbiológicos. Esse trabalho teve como foco a caracterização da matéria orgânica dissolvida (MOD) e o levantamento de estoque de metais em rios de águas brancas (AgB) e pretas (AgP) na região Central Amazônica. A amostragem de água representativas das estações seca e chuvosa e 9 de sedimentos foi realizada em um total de 15 locais. Nas amostras de água foram determinados os elementos totais e dissolvidos (Al, Cu, Cd, Cr, Fe, Pb e Ni). Estudos da labilidade e recalcitrância em termos de reatividade da MOD aquática frente a ação do H2O2, bem como a quantificação do black carbon dissolvido (DBC) (método BPCA) em rios de AgP e AgB da região, também foram realizados. Além disso, foram extraídas e caracterizadas as substâncias húmicas aquáticas (SHA) dos rios Negro (RN) e Carú (RC) e as suas interações com os cátions Al(III), Fe(III) e Cu(II) foram avaliadas. Nos sedimentos foram determinados pH, análise granulométrica e metais (Pb, Cr, Ni, Al, Fe, Cu e Zn). Concluiu-se que para águas e sedimentos, a concentração de metais esteve na sua maioria em conformidade com a legislação brasileira. Sobre a MOD, em ambos os períodos, houve o predomínio da fração recalcitrante. Entretanto, destaca-se na estação seca que o conteúdo da fração lábil foi maior para os rios de AgP e na chuvosa o contrário foi observado. A análise da fração cromófora (MODC) permitiu distinguir efeitos sazonais. No estação seca, fluoróforos do tipo húmico, C1 e C2 (autóctone e alóctone) e tipo proteico (C3) foram identificados (CP/PARAFAC). A fração fluorescente esteve relacionada ao conteúdo lábil na seca, sendo mais reativa, porém, não exibiu mesma relação no período chuvoso, sendo caracterizada pela presença de fluoróforos do tipo húmico alóctone (C4 e C5). Pela análise de UV/Vis foi observado aumento SUVA254 entre período de seca e chuva relacionado com o incremento de MOD, porém, foram observados decréscimos de SUVA254 para todas as amostras, indicando mudanças na fração MODC durante a cinética. A análise dos BPCA permitiu a determinação do DBC, variando de 0,4 a 2,8 % mol. Verificou-se variação na distribuição dos marcadores (B3CA, B4CA, B5CA e B6CA), em que B5CA e B6CA variaram de 77,9 a 94,0 % do teor de BPCA total. As %B4CA e B3CA variaram de 0,7 a 14,1 %e 3,4 a 10,0 %, respectivamente. As técnicas de Infravermelho, RMN de 13C diferenciam as SHA RC e RN estruturalmente, indicando maior porção aromática na SHA RN. Os estudos de interação com íons metálicos evidenciaram maior capacidade de complexação, bem como maior concentração de sítios ligantes para SHA RN, além da maior semelhança entre as amostras coletadas no período chuvoso, RN e RC-II.
The Amazon biome is widely known for its relevance in the climate cycles, biodiversity and extension. The area explored in this study comprised the municipalities of Itacoatiara, Maués and Manaus, located in the state of Amazonas, the first two being few explored. It is known the importance of natural organic matter (NOM) in the dynamics of other species, which is formed by defined or indefinite structures, with different degrees of lability compared to other species or to photochemical and microbiological processes. This work had as its focus the characterization of dissolved organic matter (DOM) and the inventory of metals in white (AgB) and black (AgP) water rivers in the Central Amazon region. A total of 15 water sampling sites representing dry and rainy seasons and 9 sediments were collected in rivers of the region. In the water samples, the total and dissolved elements (Al, Cu, Cd, Cr, Fe, Pb and Ni) were determined. Studies of the lability and recalcitrance in terms of the reactivity of the aquatic DOM against the action of H2O2, as well as the quantification of the dissolved black carbon (DBC) (BPCA method) in rivers of AgP and AgB of the region were also performed. In addition, the aquatic humic substances (AHS) of the Negro (RN) and Carú (CR) rivers were extracted and characterized and their interactions with Al(III), Fe(III) and Cu(II) cations were evaluated. In the sediments were determined pH, granulometric analysis and metals (Pb, Cr, Ni, Al, Fe, Cu and Zn). It was concluded that for the waters, the concentration of metals was mostly in accordance with Brazilian legislation, as well as for sediments. In the studies of the DOM, in both periods, there was a predominance of the recalcitrant fraction. However, it is noteworthy in the dry season that the content of the labile fraction was higher for the AgP rivers and in the rainy season the opposite was observed. The analysis of the chromophore fraction allowed to distinguish seasonal effects. In the dry period, humic-like fluorophores, C1 and C2 (autochthonous and allochthonous) and protein-like (C3) were identified by the CP/PARAFAC treatment. The fluorescence fraction was related to dry matter content, being more reactive, but it did not exhibit the same relationship in the rainy season, being characterized by the presence of allochthonous humic-like fluorophores (C4 and C5). By the UV/Vis analysis, SUVA254 index an increasing was observed between dry and rainy periods, related to the increment of DOM (surface runoff), however decreases of SUVA254 were observed for all samples, indicating changes in the chromophore MOD fraction during kinetics. Analysis of the BPCA allowed the determination of the DBC, which ranged from 0.4 to 2.8 mol %. Distribution of the markers (B3CA, B4CA, B5CA and B6CA) varied, which in B5CA and B6CA ranged from 77.9 to 94.0 % of the total BPCA. The B4CA and B3CA ranged from 0.7 to 14.1 % and 3.4 to 10,0 %, respectively. AHS RC and RN presented a similar aromaticity degree, but other techniques (Infrared, 13C NMR) differentiate SHA structurally, indicating a greater aromatic portion in AHS RN. The interaction studies with AHS and metallic ions showed a greater capacity for complexation, as well as a higher concentration of binding sites for AHS RN, besides the greater similarity between the samples collected in the rainy season, RN and RC-II.
The Amazon biome is widely known for its relevance in the climate cycles, biodiversity and extension. The area explored in this study comprised the municipalities of Itacoatiara, Maués and Manaus, located in the state of Amazonas, the first two being few explored. It is known the importance of natural organic matter (NOM) in the dynamics of other species, which is formed by defined or indefinite structures, with different degrees of lability compared to other species or to photochemical and microbiological processes. This work had as its focus the characterization of dissolved organic matter (DOM) and the inventory of metals in white (AgB) and black (AgP) water rivers in the Central Amazon region. A total of 15 water sampling sites representing dry and rainy seasons and 9 sediments were collected in rivers of the region. In the water samples, the total and dissolved elements (Al, Cu, Cd, Cr, Fe, Pb and Ni) were determined. Studies of the lability and recalcitrance in terms of the reactivity of the aquatic DOM against the action of H2O2, as well as the quantification of the dissolved black carbon (DBC) (BPCA method) in rivers of AgP and AgB of the region were also performed. In addition, the aquatic humic substances (AHS) of the Negro (RN) and Carú (CR) rivers were extracted and characterized and their interactions with Al(III), Fe(III) and Cu(II) cations were evaluated. In the sediments were determined pH, granulometric analysis and metals (Pb, Cr, Ni, Al, Fe, Cu and Zn). It was concluded that for the waters, the concentration of metals was mostly in accordance with Brazilian legislation, as well as for sediments. In the studies of the DOM, in both periods, there was a predominance of the recalcitrant fraction. However, it is noteworthy in the dry season that the content of the labile fraction was higher for the AgP rivers and in the rainy season the opposite was observed. The analysis of the chromophore fraction allowed to distinguish seasonal effects. In the dry period, humic-like fluorophores, C1 and C2 (autochthonous and allochthonous) and protein-like (C3) were identified by the CP/PARAFAC treatment. The fluorescence fraction was related to dry matter content, being more reactive, but it did not exhibit the same relationship in the rainy season, being characterized by the presence of allochthonous humic-like fluorophores (C4 and C5). By the UV/Vis analysis, SUVA254 index an increasing was observed between dry and rainy periods, related to the increment of DOM (surface runoff), however decreases of SUVA254 were observed for all samples, indicating changes in the chromophore MOD fraction during kinetics. Analysis of the BPCA allowed the determination of the DBC, which ranged from 0.4 to 2.8 mol %. Distribution of the markers (B3CA, B4CA, B5CA and B6CA) varied, which in B5CA and B6CA ranged from 77.9 to 94.0 % of the total BPCA. The B4CA and B3CA ranged from 0.7 to 14.1 % and 3.4 to 10,0 %, respectively. AHS RC and RN presented a similar aromaticity degree, but other techniques (Infrared, 13C NMR) differentiate SHA structurally, indicating a greater aromatic portion in AHS RN. The interaction studies with AHS and metallic ions showed a greater capacity for complexation, as well as a higher concentration of binding sites for AHS RN, besides the greater similarity between the samples collected in the rainy season, RN and RC-II.
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Matéria orgânica, Metais, Labilidade, Substâncias húmicas, Amazônia, Organic matter, Metals, Lability, Humic substances, Black carbon, Amazon