Investigation of Occurrence of Diatoms (Bacillariophyta) in Hydrographic Basins of the State of Roraima, Amazon – Brazil

Abstract

The objective of this research was to carry out a survey of the diatomaceous fluorula (Bacillariophyta) in the Branco River basin and its sub-basins in the State of Roraima (Amazonia, Brazil). The taxa were identified and presented on plates with photomicroscopy. The collections were always carried out in the dry periods, between December and March from 2000 to 2012. Sampling for qualitative and quantitative analysis was carried out through vertical and horizontal hauls in the marginal area of the rivers and with a bottom collection bottle. Bottom sediments and periphyton collections were also performed. The samples and permanent slides were designated for the reference collection of the National Institute for Research in the Amazon – INPA. 172 plankton samples at 43 sampling sites (20 in rivers and 23 in streams) were carried out. The low water period was characterized by slightly acidic to neutral pH, low transparency and typical clear water conductivity. Sixty-nine taxa distributed in three classes, 10 orders, 15 families and 20 genera were identified. The most representative orders were Naviculales (38%), Eunotiales (26%) and Surirellales (9%). The families with the highest representation were Eunotiaceae (26%), Pinnulariaceae (19%) and Surirellaceae (9%). The species with the highest frequency of occurrence and representativeness in the integrated river-igarapé system were: Actinella sp., Aulacoseira ambigua, A. granulata, A. pseudogranulata, Aulacoseira sp., Frustulia rhomboides, Surirella linearis, and Synedra goulardii var. fluviatilis.