Ecology of the epilithic diatom community in a low-order stream system of the Guaíba
hydrographical region: subsidies to the environmental monitoring of southern Brazilian aquatic systems
HERMANY1, G., SCHWARZBOLD1, A., LOBO2, E.A. & OLIVEIRA3, M.A.
1 Ecology Department, Biosciences Institute. Federal University of Rio Grande do Sul – UFRGS - Av. Bento Gonçalves, 9500, Campus do Vale, Porto Alegre, RS, Brazil.
guilherme.hermany@ufrgs.br; albano@ecologia.ufrgs.br
2 Laboratory of Limnology. University of Santa Cruz do Sul – UNISC - Avenida Independência 2293, Santa Cruz do Sul, RS, Brazil. lobo@unisc.br
3 Department of Biology, CCNE, Federal University of Santa Maria – UFSM – Av. Roraima, S/N, Campus Camobi, Santa Maria, RS, Brasil. CEP 97105-900.
ABSTRACT: From the relationship between the structure of epilithic diatom communities in the Schmidt Stream - a small water course in the Guaíba hydrographical region, RS, Brazil – and changes in water quality, as well as physical alterations of the environment such as flow, riparian shading, width and depth of the channel, this study aimed to gather subsidies to be applied in aquatic ecosystem monitoring and conservation programs. Between January and February 2004, four field trips were conducted to six sampling sites, adding up to 24 samples. Analysis of the epilithic diatom community was carried out on samples scrubbed off five replicated stones, representing a total area of 125 cm2. Samples were cleaned with k2Cr207, H2SO4 and HCl prior to the assembly of permanent glass slides. Species distribution and abundance patterns were explored through the use of the Indicator Species Analysis and environmental factors influencing this configuration were singled out by Canonical Correspondence Analysis. The results confirmed the preference of the genera Cymbella and Encyonema for environments where slow current and high luminosity prevail, and the adaptability of Cocconeis to shading. The species Nitzschia acicularis and Surirella tenera were found to be good indicators of meso-eutrophic conditions. Encyonema perpusillum stood out as a representative of oligo/b-mesossaprobic habitats, while Sellaphora pupula was abundant in ion-rich environments. Comparing the species responses to oxygen saturation, BOD, COD, conductivity, total phosphorus, total dissolved solids and turbidity, two indicator groups were established.
Key-words: periphyton, natural substrata, lotic environments, biomonitoring.