<i>Pinnularia</i> (BACILLARIOPHYTA) RICHNESS VARIATION IN TUPÉ LAKE (AMAZON BASIN) AND ITS HYDROLOGICAL CYCLE RELATION

The Amazon floodplain lakes are subject to yearly fluctuations of water levels and rivers and/or igarapés contributions that have influence in their limnological and biological characteristics. Among the organisms found in the plankton the Pinnularia genus stands out as representative in number of species. This study aims to evaluate the richness of Pinnularia in the Tupé Lake, Rio Negro Basin and its hydrological cycle relation. Samplings with plankton net were carried out in bimonthly scale in three different stations in this lake, covering falling and low waters periods (2002/2003) and the rising and high waters (2003/2004). The results showed that the falling – low waters period presented a significantly higher richness (52 taxa) in comparison to the rising – high waters period, when we observed 33 taxa. The highest richness in the falling – low waters period is probably related to waters coming from “igarapés” and the vertical circulation of the water column, which in this period keeps a greater interface between water-sediment promoting the benthic organisms suspension in the system. Keywords: black waters; diatoms; floodplain lake; South America