RESUMO
Riverine ecosystems can be conceptualized as 'bioreactors' (the riverine bioreactor) which retain and decompose a wide range of organic substrates. The metabolic performance of the riverine bioreactor is linked to their community structure, the efficiency of energy transfer along food chains, and complex interactions among biotic and abiotic environmental factors. However, our understanding of the mechanistic functioning and capacity of the riverine bioreactor remains limited. We review the state of knowledge and outline major gaps in the understanding of biotic drivers of organic matter decomposition processes that occur in riverine ecosystems, across habitats, temporal dimensions, and latitudes influenced by climate change. We propose a novel, integrative analytical perspective to assess and predict decomposition processes in riverine ecosystems. We then use this model to analyse data to demonstrate that the size-spectra of a community can be used to predict decomposition rates by analysing an illustrative dataset. This modelling methodology allows comparison of the riverine bioreactor's performance across habitats and at a global scale. Our integrative analytical approach can be applied to advance understanding of the functioning and efficiency of the riverine bioreactor as hotspots of metabolic activity. Application of insights gained from such analyses could inform the development of strategies that promote the functioning of the riverine bioreactor across global ecosystems.
Assuntos
Mudança Climática , Ecossistema , Reatores Biológicos , Cadeia AlimentarRESUMO
The aim of this study was to assess of composition and structure of ichthyofauna over two distinct periods: three and eleven years after the establishment of the protected area. The results of composition and structure of the ichthyofauna of the Diamante River, sampled quarterly from November 2005 to August 2006, were compared to results obtained by Abilhoa and Bastos (2005) in studies conducted between August 1997 and December 1998. The 2.4 to 16 cm-mesh gillnets were exposed for 24 hours and checked every 8 hours. In order to characterize the ichthyofauna, patterns of species richness, diversity, evenness and frequency of occurrence of species were analyzed. A total of 673 individuals, distributed among 36 species, 13 families and four orders were sampled. Significant changes were found in ichthyofauna composition, with a reduction in diversity and evenness as compared to the previous study. The high representativeness of alien species indicates instability in the studied area, through changes in diversity, species replacement, predominance of opportunistic species, and physical changes such as silting and degradation of the body of water.
O objetivo do presente trabalho foi investigar as assembleias de peixes do ribeirão Diamante (Estação Ecológica do Caiuá), visando avaliar sua composição e estrutura, ao longo de dois períodos distintos: três e 11 anos após sua criação. Para tanto, foram comparados os resultados obtidos nas amostragens realizadas trimestralmente no presente estudo, entre novembro de 2005 e agosto de 2006, com os resultados apresentados por Abilhoa e Bastos (2005) para o período de agosto de 1997 a dezembro de 1998. Neste estudo, os aparelhos de pesca foram constituídos de redes de espera simples com malhas de 2,4 a 16 cm (entre nós opostos), expostas por 24h, com revistas a cada 8h. Para a caracterização da ictiofauna, foram analisados padrões de riqueza específica, diversidade, equitabilidade e frequência de ocorrência das espécies. Foram capturados 673 indivíduos, distribuídos em 36 espécies, 13 famílias e quatro ordens. Verificou-se significativa alteração na composição da ictiofauna do ribeirão, com redução na diversidade e equitabilidade em relação ao trabalho anterior. Observou-se alta representatividade de espécies exóticas, o que indica instabilidade na área de estudo pelas alterações na diversidade, substituição de espécies, predomínio de oportunistas e alterações físicas como assoreamento e degradação do corpo de água.