Biofilms coating Schoenoplectus californicus as indicators of water quality in the Río de la Plata Estuary (Argentina) Delia E. Bauer & Nora Gómez & Paula R. Hualde Received: 23 May 2006 / Accepted: 20 November 2006 / Published online: 10 February 2007 # Springer Science + Business Media B.V. 2007 Abstract Community composition, structure, bio- mass and tolerance to pollution of biofilms growing on Schoenoplectus californicus were assessed, togeth- er with physico-chemical parameters of the water, to evaluate their usefulness as water quality indicators along the Argentinian shore of the freshwater zone of the Río de la Plata Estuary. Monthly sampling was carried out at three sites, one of which, located in a nature reserve, was considered as the reference site while the others were affected by sewage outlets and port activity. The reference site had higher dissolved oxygen and turbidity values, the polluted sites greater conductivity, oxygen demands, phosphate, ammoni- um and nitrite values. Diatoms dominated the biofilms at the reference site; ciliates reached higher densities at the polluted sites. Significant differences were found in species numbers, species diversity index, biomass, tolerance to pollution of the taxa, and the Pampean Diatom Index, between the reference and the impacted sites. This study shows that the biofilms growing on Schoenoplectus californicus are good indicators of the changes in the water quality of their environment. Keywords Biofilms . Río de la Plata Estuary . Schoenoplectus californicus . Water quality indicator Introduction Physical, chemical and bacteriological variables com- monly form the basis of water quality monitoring because of their ability to detect changes in the environment in a rapid and straightforward manner. These traditional measurements, however, provide no information as to the effects of such changes on the biological communities, which are ultimately affected by altered environmental conditions (Vis et al. 1998). Several studies have demonstrated that many peri- phyton characteristics are related to water quality (Ács et al. 2003, 2004, 2006; Cattaneo 1987; Ector and Rimet 2005; Kiss et al. 2002; Lowe and Pan 1996; McCormick and Stevenson 1998; Szabó et al. 2004, 2005) but the use of epiphytic communities presents a number of methodological problems especially when the community is used for monitoring purposes. However, when the substratum is largely covered by hydrophytes the epiphytic organisms on their surfaces are often important and should be considered, therefore they can be used to assess water quality (Cazaubon 1996). Environ Monit Assess (2007) 133:309–320 DOI 10.1007/s10661-006-9586-x D. E. Bauer : N. Gómez : P. R. Hualde Instituto de Limnología Dr. R. A. Ringuelet (CONICET-UNLP), C. C. 712 (1900), La Plata, Argentina Present address: D. E. Bauer (*) Instituto de Limnología Dr. R. A. Ringuelet, C. C. 712 (1900), La Plata, Argentina e-mail: debauer@ilpla.edu.ar