Spatial and seasonal variation of the epilithic diatom: a case study of organic pollution gradient a subtropical region of southern Brazil

Saionara Eliane Salomoni


Abtract: Aim: The variation in the density and composition of epilithic diatoms related to environmental and climatic variables was studied along the Gravataí river basin, embracing the upper course with its agricultural activity and the lower course impacted by the industrial and urban residuary waters.  Methods: Samples were collected on rocky substrates at six station quarterly from September/2000 to August/2002. A marked seasonality was observed with a difference of 15°C between summer and winter. The standard of precipitation resulted in variations in nutrient availability. Results: The diatom community reflected these changes in species composition and in the population density. The highest densities occurred in the fall, reaching a maximum value of 13,363 ind/cm2. The species Cocconeis placentula and Eolimna minima were abundant during the fall, while Gomphonema parvulum, Eunotia pectinalis and Navicula radiosa reached higher densities in the winter. Conclusion: The seasonal variation was more evident at the river’s upper course, a low eutropication and organic contamination site. At the low course, with greater anthropic impact, Nitzschia palea and Sellaphora seminulum remained present in the four seasons of the year and gradually became dominant therefore showing that the ephilitic diatoms seasonal variation is affected by the contamination and the eutrophication of the system. 


epilithic diatoms density, taxonomic composition, impacted system.

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