In the current search for renewable energy sources, residual biomass has gained ground in the concept of biorefinery. Furanic compounds such as 5-hydroxymethylfurfural (HMF), furfural (FF) and derivatives such as levulinic acid (LA), obtained from biomass, have emerged as important industrial chemical platforms. In this sense, this work aimed to use pequi bark, typical biomass and abundant in the Brazilian cerrado, in the production of HMF, FF and LA using the ionic liquid 1-n-butyl-3-methyl-imidazole bromide ([BMIM][Br]). The analysis of chemical composition of pequi bark showed that it has potential for use in the production of bioproducts, FF, HMF and LA, with yields of 65, 3 and 23.7%, respectively. High glucose conversion rates were found (> 90%). The analysis of variance (ANOVA) was applied to obtain the mathematical model with α = 0.05, verifying the significance of the second order model established for HMF (F = 0.00167) and FF (0.004494). The model fit is satisfactory, obtaining the coefficient of determination (R2) for the HMF and for the FF of 0.9599 and 0.08422, respectively. From the results obtained, it can be concluded that pequi bark has good precursor capacity for use in biorefinery processes.

Resumo Medidas simultâneas de produção (PB) e respiração bacterianas (RB) são indispensáveis para o entendimento da magnitude do ciclo do carbono nos níveis tróficos mais basais dos sistemas aquáticos, mas são ainda escassas nos trópicos. O presente estudo foi realizado em um estuário extremamente produtivo (Porto do Recife, 08°03'S; 34°52'W, NE do Brasil), onde a demanda bacteriana por carbono (DBC=PB+RB) e a eficiência de crescimento bacteriano (ECB=PB/DBC) foram determinadas para estimar o principal papel do bacterioplâncton: fonte ou captador de carbono orgânico. Apesar das altas taxas de PB (0.03-0.4 µMC h-1), as taxas extremas de RB (0.5-4.1 µMC h-1) levaram a baixa ECB (0.02-0.29), provavelmente devido às altas temperaturas (>25ºC) e forte limitação por nitrogênio inorgânico (razão N:P) A alta DBC e a baixa ECB indicam que o bacterioplâncton esteja atuando principalmente como remineralizador da matéria orgânica dissolvida, alimentando a produção primaria do sistema. Esses resultados contradizem o que seria esperado baseado em estudos conduzidos em estuários eutróficos temperados (onde geralmente ECB > 0.30) e apontam para a importância de se aumentar estimativas in situ de PB e RB em sistemas estuarinos tropicais a fim de se promover um melhor entendimento do papel desses sistemas na ciclagem de carbono global.

Abstract Simultaneous measurements of bacterioplankton production (BP) and respiration (BR) are imperative to understand the magnitude of carbon cycle in the lower trophic levels of the aquatic systems, but are still scarce in the tropics. The present study was performed in a highly productive estuary (Recife harbor, 08°03'S; 34°52'W, NE Brazil) where bacterial carbon demand (BCD=BP+BR) and growth efficiency (BGE=BP/BCD) were evaluated in order to estimate the major role of bacterioplankton: source or sink of organic carbon. In spite of the high BP rates (0.03-0.4 µMC h-1), the extremely high BR rates (0.5-4.1 µMC h-1) led to low BGE (0.02-0.29), possibly due to the high temperatures (>25ºC) and strong inorganic nitrogen limitation (N:P ratios) The high BCD and low BGE indicate the major role of bacterioplankton as dissolved organic matter remineralizers, fueling the primary productivity of the system. These findings contradict what could be expected from studies in highly productive temperate estuaries (where BGE is usually > 0.30) and highlight the importance of increasing in situ BP and BR estimates in tropical estuarine systems in order to better understand the role of these systems in global carbon cycling.

A dinâmica dos vários compartimentos do plâncton foi avaliada durante uma série de curta duração na entrada da baía de Guanabara (SE do Brasil), com o objetivo de estimar suas correlações tróficas. A biomassa e eficiência fotossíntética das três frações do fitoplâncton (picoplâncton: < 2µm, nanoplâncton: 2-20µm e microplâncton: > 20µm), juntamente com a composição e abundância do nano-e microplâncton auto-e heterótrofos e do mesozooplâncton, foram determinadas em uma estação fixa durante 3 dias consecutivos, a intervalos de 3h, nas camadas de superfície e de fundo (20m). A variabilidade de quase todos os compartimentos do plâncton na superfície foi diretamente relacionada à temperatura, indicando forte influência da circulação da entrada da baía na estrutura planctônica. Na camada superficial, o mesozooplâncton parece ser alimentado pelo nano-e picoplâncton autótrofos, esse último sendo sustentado pelo microzooplâncton. Próximo ao fundo, o microplâncton auto-e heterótrofo estão possivelmente sustentando a biomassa mesozooplanctônica. Nossos resultados sugerem, portanto, que na entrada da baía de Guanabara esteja estabelecida uma rede trófica multívora, i.e., uma combinação entre as cadeias microbiana e de pastagem.

The dynamics of the plankton compartments at the entrance of Guanabara Bay (SE Brazil) were assessed during a short-term temporal survey to estimate their trophic correlations. Size-fractioned phytoplankton (picoplankton: < 2µm, nanoplankton: 2-20µm and microplankton: > 20µm) biomass and photosynthetic efficiency, composition and abundance of the auto-and heterotrophic nano-and microplankton, and mesozooplankton were evaluated at a fixed station for 3 consecutive days at 3-h intervals, in the surface and bottom (20m) layers. The variability of almost all plankton compartments in the surface layer was directly dependent on temperature, indicating the great influence of the circulation at the entrance of the bay on plankton structure. In the surface layer, the mesozooplankton seems to be sustained by both autotrophic nano-and picoplankton, this last being channeled through the microzooplankton. Near the bottom, both auto-and heterotrophic microplankton are probably supporting the mesozooplankton biomass. Our findings thus suggest that the entrance of Guanabara bay presents a multivorous food web, i.e., a combination of both grazing and microbial trophic pathways.