versão impressa ISSN 0366-5232
Community structure of benthic diatoms was studied on three natural substrates in three areas along the Tota stream to determine the environmental factors related to the distribution of diatoms in different areas and on different substrates along a longitudinal gradient. Community composition was analyzed and contrasted using multiple comparison tests, ANOVA, and ordination techniques. Only the flow and the temperature showed synchronization with hydroclimatic regime, while pH and nutrient concentration showed a different pattern. Through periods of low flow, Melosira varians was dominant upstream, while Rhoicosphenia abbreviata was dominant downstream. During high flow periods R. abbreviate dominated in all reaches. The highest diversity was registered during flood times. The sampled areas showed different responses to flow action; the highest area was less affected, while the lowest area exhibited a positive relation with higher flow. No difference was found in diatom composition or diversity on the three substrates. Tota stream is a low diversity system with slight changes along its length and among substrates, and its diatom community responds to hydroclimatic-seasonal changes and nutrient gradients.
Palavras-chave : Longitudinal gradient; Flow; Phosphates; natural substrates; reaches.