Fluxo de carbono em teias tróficas e métricas de estrutura trófica da comunidade de rios florestados e impactados da bacia do rio Guapi- Macacu, Rio de Janeiro

Abstract

We estimated the primary production of algae of the periphyton, the secondary production of macroinvertebrates and used stable isotopes of carbon e nitrogen to quantify the flows of material in food webs and the trophic structure of community of forested and disturbed streams in the Guapi-Macacu catchment, Rio de Janeiro, Brazil. In forested streams, the average ingestion flow was 16.21 (amplitude = 7.42 - 26.90) g of dry mass.m-2.year-1, the allochthonous material flow represented between 71 to 87% of basal source flow to macroinvertebrates, the remainder was derived of autochthonous production. While, in streams that had their riparian vegetation reduced for land use (agriculture and urbanization), the flow ingested was 2.87 and 7.82 g of dry mass.m-2.ano-1, the allochthonous material flow represented between 28 and 74% of basal source flow to macroinvertebrates, the remainder was derived of autochthonous production. In both environments, less than 3% of autochthonous production is ingested in one year, while the predators can ingest between 22 to 139% of primary consumers production. Few taxa, 2 or 3, had strong influence in the energy flow in the food web. In the preserved environment, these key-taxa were the shredder caddisfly Triplectides (Leptoceridae) or the collector-filterers Leptonema or Smicridea (Hydropsychidae) or the shredder cranefly Tipulidae; while in the perturbed environments, the midge Chironomidae stood out. The trophic structures of community in stream with disturb show diversity of trophic level, of basal source and trophic diversity different of the forested streams. The work suggests that the material flow in the food web in streams was sensitive to land use. In spite of being more expensive and laborious than the majority of the parameters usually used for impact assessment and monitoring, material flow can be complement in investigation of the cause-effects cascade.