Decomposição foliar e produção secundária como indicadores funcionais em um gradiente de impacto de cobertura do solo ripário em rios tropicais

Abstract

Currently the biggest threat to the integrity of aquatic ecosystems lies in human actions, which through changes in riparian vegetation, reach all compartments of river systems by changing the physical structure, chemical and biological river and connecting patterns between terrestrial ecosystems and water. Macroinvertebrate shredders importance is not well known in the tropics. They can contribute to leaf decomposition in streams, which is a fundamental process for energy flow in small rivers. Leaf decomposition and aquatic macroinvertebrates secondary production processes in stream ecosystems are closely related to the contribution of terrestrial vegetation, and may be sensitive to changes in riparian vegetation. The objectives of this study were to assess: (a) what changes deforestation can cause the physical and chemical parameters of rivers; (B) the effects of deforestation on benthic macroinvertebrate community structure associated with leaves, (c) the effects of deforestation in ecosystem processes such as leaf decomposition and secondary production, and (d) the association between shredders secondary production and leaf decomposition. The study was conducted in 27 sites distributed in four streams (7-8 sites per river) from second to third order that had deforestation gradient. To estimate decomposition rates five leaf packs were immersed in each of the points. A leaf pack was removed from each after 2, 7, 15 and 28 days of immersion. The fifth leaf pack was removed on the 37th day of immersion to estimates of secondary production, biodiversity and functional diversity of aquatic insects. The ammonium concentrations increased and species richness of aquatic insects and EPT (Ephemeroptera, Plecoptera and Trichoptera) of leaf packs decreased with increase of deforestation. The decomposition rates decreased with increasing deforestation. The data suggest that the loss of riparian vegetation in the agricultural conversion impacted chemical and biotic parameters in both macroinvertebrate community structure and the functioning of the ecosystem. We conclude that the restoration and preservation of riparian vegetation must be a central focus of stream ecosystems management strategies to ensure that ecosystem processes and community structure in river basins are acting as providers of the expected environmental services.