Response of epilithic diatom communities to environmental gradients in subtropical temperate Brazilian rivers

Abstract

This work aims to analyse the response of epilithic diatom communities to environmental gradients in subtropical temperate southern Brazilian rivers to contribute to the development of a widely applicable methodology for water-quality monitoring. Samples for physical, chemical and biological determination were collected monthly, from December 2001 to November 2002 and from March 2003 to February 2004, at 9 stations along the rivers Pardo and Pardinho in the hydrographical basin of Rio Pardo, State of Rio Grande do Sul (RS), Brazil. Physical and chemical variables (water temperature, pH, dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, nitrates, nitrites, phosphates and total dissolved solids) and biological variables (epilithic diatom communities) were used as parameters for water-quality assessment. The data matrix was examined by means of a multivariate ordination using Detrended Correspondence Analysis (DCA). In total, 270 taxa were identið€€‚ed to specið€€‚c or infra-specið€€‚c levels. The results showed that of all the physical and chemical variables used, the main gradient along the DCA ð€€‚rst axis was eutrophication, which was indicated by its signið€€‚cant correlation with phosphates ( p < 0.001). Hence, the species’ scores on the DCA axis were used as an operational criterion for indicating their tolerance to eutrophication. From this analysis, the 10 taxa that were the most tolerant to eutrophication were: Cyclotella meneghiniana, Fallacia monoculata, Nitzschia acicularis, N. clausii, N. nana, N. palea, Nitzschia sp., Pinnularia sp., Sellaphora pupula sensu lato and Ulnaria acus. The present study showed that epilithic diatom assemblages reð€€ƒect anthropogenic changes in hydrographic basins in subtropical temperate streams, especially pollution by organic enrichment and eutrophication