Composition and dynamics of allochthonous organic matter inputs and benthic stock in a Brazilian stream

Riparian vegetation provides the nutrient and energy input that maintains the metabolism and biodiversity in tropical headwater streams. In the present study, it was hypothesised that similar to 30% of riparian plant species contribute over 70% of coarse particulate organic matter and, because tropical plants are perennial and semi-deciduous, it was expected that leaf fall would occur year round. The aims of the present study were to evaluate the composition and structure of the plant riparian zone and the input and associated benthic stock of organic matter. The riparian vegetation was composed of 99 taxa. The most abundant plant species were Tapirira obtusa, Sclerolobium rugosum, Croton urucurana, Byrsonima sp. and Inga sp. The input and benthic stock showed a seasonal pattern, with higher values recorded at the end of the dry season and at the beginning of tropical storms. The biomass contributed monthly by the vegetation ranged from 28 +/- 6 g m(-2) to 38 +/- 11 g m(-2), and the mean monthly benthic standing stock was 138 +/- 57 g m(-2). The results illustrate the importance of riparian vegetation as an energy source to tropical streams and how individual plant species contribute to organic matter inputs in these ecosystems.