Longitudinal variation of periphytic algal community structure in a tropical river

Abstract

The present study evaluated the influence of abiotic factors on the periphytic algal community structure under different environmental conditions. Six sampling sites were established along the course of the Sao Mateus River: two upstream of the city of Sao Mateus (E1, E2), two along the city (E3, E4), and two downstream of the city (E5, E6). Biotic and abiotic samplings were performed every week, in September and October 2010, totaling four collections. The periphyton was collected from roots of Eichhornia crassipes (Mart.) Solms. removed by scraping with brushes and jets of distilled water, fixed and preserved with formalin 4 % (qualitative analyses) and with acetic lugol 5 % (quantitative analysis). Higher richness of taxa and total density of periphytic algal community were registered in the sampling sites along and downstream of the city of Sao Mateus, with a greater contribution of Bacillariophyceae (richness) and Cyanophyceae (total density) in all sampling sites. The periphytic algal density was influenced by nutrients (especially nitrogen) and turbidity, as evidenced by the CCA. Thus, it is suggested that the input of allochthonous matter, especially from human activities (intensive fish farming and discharge of domestic and industrial wastewaters) change the water quality (as evidenced by the PCA), as well as communities of periphytic algae present.