Hydrochemical conditions in the açu lagoon are described using spatial and temporal variations of various limnological variables (water temperature, dissolved oxygen, electric conductivity, total alkalinity, carbon dioxide, dissolved and total nutrients (n, p and Si), and chlorophyll a). collected data was used in order to understand the structure and functioning of an enclosed coastal lagoon strongly influenced by climatic conditions. Water samples were collected monthly (november 1999-december 2000) in five sampling stations established along the lagoon. a decreasing spatial gradient of electrical conductivity was observed beginning from a sand bar region between the lagoon and the sea in the direction of the sweet-water input area. the positive correlation observed between the pH and dissolved oxygen (do) values, and the negative one observed between pH values and those of carbon dioxide (co 2 ), evidenced coupled biological processes, e.g., primary production and decomposition. Both spatial and temporal variation of dissolved nutrients showed fast increase and decrease in the beginning of summer, suggesting that nutrient input resulting from rainfall stimulates phytoplankton production, as reflected by chlorophyll a concentration increase.Keywords: coastal lagoon, hydrochemistry, dissolved nutrients. RESUMOVariação sazonal da hidroquímica em uma lagoa costeira tropical (Lagoa do Açu, Brasil) condições hidroquímicas da lagoa do açu são descritas usando a variação espacial e temporal de algumas variáveis limnológicas (temperatura da água, oxigênio dissolvido (od), condutividade elétrica, alcalinidade total, co 2 , nutrientes dissolvidos e totais (n, p, Si) e clorofila a para entender a estrutura e funcionamento de uma lagoa costeira isolada e fortemente influenciada pela sazonalidade. amostras de água foram coletadas mensalmente (novembro 1999 a dezembro 2000) em cinco estações de amostragem estabelecido ao longo da lagoa. um gradiente espacial decrescente de condutividade elétrica foi observado da região da barra de areia, que separa a lagoa do mar, em direção a região que recebe entrada de água doce. a correlação positiva entre os valores de pH e oxigênio dissolvido, e negativa observada destes com o co 2 , evidencia o acoplamento de processos biológicos, como o de produção primaria e de decomposição. a variação espaço temporal de nutrientes dissolvidos mostrou um rápido incremento e redução da concentração de nutrientes dissolvidos no inicio do verão, sugerindo que a entrada de nutrientes pelas chuvas é um fator que estimula o crescimento fitoplanctônico, refletido pelo aumento da concentração de clorofila a.Palavras-chave: lagoa costeira, hidroquímica, nutrientes dissolvidos.
In the Neotropics, there is a great diversity of aquatic environments characterized by their shallowness, which facilitates colonization by aquatic macrophytes (Esteves, 2011). In these systems, aquatic macrophytes play an important role in the ecosystem dynamics because they have high biomass production and because they are the most abundant sources of organic matter. In these well vegetated shallow water bodies, macrophyte decomposition represents the main nutrients cycling mechanism (Scheffer, 2001;Shilla et al., 2006), releasing nutrients for the primary producers (Battle and Mihuc, 2000;Xie et al., 2004).This process generally has two distinct phases (Esteves and Barbieri, 1983;Silver and Miya, 2001). First, the physical processes of leaching and cellular lysis occur, releasing the nonstructural soluble fractions, such as carbohydrates, proteins, phosphate and potassium (Bastardo, 1981). During this phase, invertebrates are the main supporters of the fragmentation processes (Bianchini Jr., 2003). During the second phase of degradation, biological processes are dominant as a consequence of the catabolic action of detritivorous organisms. These organisms promote partial or total breakdown of the particulate organic matter (POM), especially by enzymatic activity (Vrba et al., 2004). This second phase is slower than the first, especially in presence of detritus which is rich in refractory structural compounds (Bianchini Jr., 2003).The submerged aquatic macrophyte Egeria densa Planchon grows by forming extensive stands, especially in alkaline environments (Bini and Thomaz, 2005); it is the dominant primary producer in the Campelo Lake (Northern of Rio de Janeiro State, Brazil) and directly affects nutrient cycling in the lake. This macrophyte is reported to have low lignocellulosic fiber content (Nunes et al., 2011), resulting in an accelerated breakdown rate of the detritus.The present study aimed to i) evaluate the decomposition process of E. densa in the Campelo Lake; and ii) infer the importance of this process for the nutrient release to the water column. The rate of the decay process resulting from microbial degradation was compared with decomposition rates that included additional exposure to invertebrate organisms, using litter bags of two different mesh sizes (45 µm and 2 mm). We hypothesized that the process mediated by microorganisms alone (45 µm mesh) would not be slower than that mediated by microorganisms plus invertebrates (2 mm mesh), due to the labile composition of detritus. Moreover, the experiments were conducted during two seasons: a dry season (September
-(Temporal variations in the primary productivity of Eleocharis acutangula (Cyperaceae) in a tropical wetland environment). Wetland vegetation typically includes aquatic macrophytes with high primary production capacities. The present study investigated how hydrological variations affect biomass allocation and primary productivity in the emergent macrophyte Eleocharis acutangula (Roxb.) Schult. Eleocharis acutangula ramets were collected from the Campelo Lagoon flood plain (21°39' S, 41°12' W and 21°37 S, 41°11' W) between March/2005 and February/2006. This region experienced an unusually short rainy period between November/2005 and February/2006 that generated atypically high primary production levels (128 gDW m -2 month -1 ) and total biomass gains (447 gDW m -2 ) in May and June/2005 respectively. Our data indicated that primary production and biomass allocation were strongly influenced by variations in wetland water levels and that macrophytes quickly invested in biomass accumulation when surface water levels rised.
Análise crítica dos estudos sobre metano desenvolvidos no Brasil Análise crítica dos estudos sobre metano desenvolvidos no BrasilEste artigo avalia a produção bibliográfica gerado por pesquisadores e centros de pesquisa nacionais acerca da contribuição aos ambientes aquáticos brasileiros para a emissão de gases de efeito estufa, relevância das publicações e se há concentração dos trabalhos em determinadas regiões do Brasil. A análise dos artigos científicos demonstrou que a participação de pesquisadores brasileiros ainda é pequena. Os trabalhos estão concentrados na região amazônica, não sendo observada nenhuma iniciativa nas regiões sul e nordeste. Desta forma, espera-se que os estudos futuros possam abranger uma maior variedade de ecossistemas, cobrindo lacunas importantes nas demais regiões do País. Palavras-chave: Pesquisa nacional. Gases de efeito estufa. Hidrelétricas. Áreas alagadas.This article evaluates the scientific knowledge generated by researchers and national research centers concerning how greenhouse gases affect Brazilian water systems, relevant publications on this issue and whether these studies are concentrated in certain areas of the country. Analysis of scientific articles demonstrated that participation of Brazilian researchers is still small. Research is concentrated in the Amazon region, with no findings in the southern and northeastern regions. One expects that future studies will consider a greater variety of ecosystems, filling important gaps in other regions of the Country.Nas últimas duas décadas, vários estudos sobre a concentração e fluxo de gases de efeito estufa (especialmente CO 2 e CH 4 ) têm sido realizados, em lagos e rios naturais e represas em todo o mundo, mostrando que estes ambientes podem contribuir de forma significativa para o efeito estufa (BARTLETT; HARRISS, 1993). Os ambientes aquáticos produzem estes gases biogênicos no processo de decomposição da matéria orgânica produzida dentro do ambiente (autóctone) ou na que é importada da bacia de drenagem (alóctone). Estima-se que estes ambientes contribuem com cerca de 40% da emissão global de metano para a atmosfera (KHALIL; SHEARER, 1993).O metano é produzido pela degradação anaeróbica de compostos orgânicos, e inundações de sedimentos ricos em matéria orgânica em ambientes de água doce e Critical analysis of methane research carried in Brazil
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