The potential use of epilithic diatoms as indicators of organic pollution was evaluated in Gravataı´River, RS, (latitude 29°45¢-30°12¢ S; longitude 50°27¢-51°12¢ W). The river suffers agricultural impacts in its upper course and urban and industrial organic pollution in its lower course. Epilithic diatoms were sampled eight times from September 2000 to August 2002, at six sites. Species were identified and densities and relative abundances of populations were determined. Simultaneously, physical, chemical and microbiological variables were measured (water temperature, conductivity, turbidity, pH, dissolved oxygen, biochemical oxygen demand (BOD 5 ), chemical oxygen demand, ammonium, organic nitrogen, total nitrogen, ortho-phosphate, total phosphate, chloride and faecal coliforms). In order to interpret the environmental and biological variables, discriminant analysis and the TWINSPAN methods (Two-Way Indicator Species Analysis) were applied. The results indicated that the concentrations of ortho-phosphate, ammonium, total organic nitrogen, BOD 5 and faecal coliforms characterized a pollution gradient along the river, where changes in the abundance or species composition were observed. Species were classified into three groups: Group A, including species more tolerant to heavy organic pollution and eutrophication, represented by
São apresentados os resultados do estudo do metafíton, bentos e de comunidades fitoplanctônicas ocorrentes em ambientes lênticos de Charqueadas e municípios vizinhos, região esta sujeita à influência de mineração e processamento de carvão mineral. O estudo baseou-se em 46 amostras coletadas em julho e agosto de 1986. Dos 213 táxons específicos e infra-específicos identificados, 95 constituem-se em primeiro registro de ocorrência no Estado. Os grupos melhor representados quanto ao número de espécies ocorrentes foram Chlorophyta (Desmídias) e Bacillariophyta (Diatomáceas). Foi constatada presença de espécies indicadas na literatura como organismos de ambientes ácidos, com maior representatividade no bentos e metafíton de biótopos sujeitos à influência direta de rejeito de carvão. Nesses sistemas ácidos, foi registrada no fitoplâncton dominância de organismos nanoplanctônicos da classe Chrysophyceae, estando quantitativamente bem representadas, no bentos, as Euglenophyta, Bacillariophyta e Chlorophyta. A estrutura das comunidades fitoplanctônicas mostrou baixos índices de diversidade, caracterizando um desequilíbrio na composição específica das mesmas.
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