Epilithic diatom community in a high altitude stream impacted by fish farming in southern Brazil
Abstract
The aim of this study was to determine the community structure of epilithic diatom in a 3rd order stream in southern Brazil, at an altitude of approximately 1,000m, in a stretch impacted by fish farming effluents. From July 2005 to February 2006, samples of diatoms on stones were collected monthly, with the physical and chemical water variables, in four sampling stations, two were located upstream and two downstream of the fish farming. The epilithic diatom community was represented by 48 taxa and the results revealed the occurrence of an impact gradient associated to the fish farming effluents, with a significant increase in the levels of nutrients and total solids downstream. The diatom community responded to trophic enrichment with a clear substitution of species characteristic to oligotrophic environments by indicator species of eutrophic environments. Throughout the Indicator Species Analysis, it was possible to identify two groups of species. The first group, composed by Gomphoneis rhombica, Navicula angusta, and Planothidium frequentissimum indicated environments with little impact, low availability of nutrients, small quantity of total solids, and low turbidity. The second composed, by Luticola goeppertiana, Melosira varians, Nitzschia palea , Gomphonema parvulum, Navicula cryptotenella, and Psammothidium subatomoides indicated eutrophic waters. So, epilithic diatoms demonstrated be a useful tool in biomonitoring impacts caused by eutrophication.
