Is the River Continuum Concept valid for Atlantic Forest rivers in Southeastern Brazil?

Abstract

The majority of the present models that explain the functioning of river ecosystems was based in data obtained from temperate or subtropical rivers, especially from the northern hemisphere. So, the adequacy of these models to the conditions found in the tropics demand an evaluation of their predictions. In this way, a study was performed in two Atlantic Forest rivers from the basin of Macaé River, in the State of Rio de Janeiro. The work was performed along a longitudinal gradient, including sections from the 1^th (1,100 m) to the 6^th (20 m) orders. The aquatic insects sampled were separated in Operational Taxonomic Units (OTUs) and classified according to trophic functional categories based on direct observations and data from the literature. The resu1ts are compared and discussed from the hypotheses presented by the River Continuum Concept (RCC), proposed by VANNOTE et al. in 1980, whose predictions were partially confirmed. Thus, the greatest diversity was observed in reaches where there is a transition from a predominantly heterotrophic zone to an autotrophic area (4^th order). 1t was also observed that there is a trend in the increase of fine particulate organic matter and in the decrease of the coarse particulate organic matter along the longitudinal gradient of the river. The percentages of biomass variation in the trophic functional categories showed a pattern similar to the modifications expected by the RCC according to the increase of the river size.