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Ecología austral

versión On-line ISSN 1667-782X


PIZARRO¹, Haydé E  y  ALEMANNI, María E. Physical and chemical variables of the water and its influence on the periphytic biomass on the lower parts of the Luján river (Buenos Aires Province). Ecol. austral [online]. 2005, vol.15, n.1, pp.73-88. ISSN 1667-782X.

The influence of some physical and chemical variables of the water on the periphyton (dry weight, ash, ash-free dry weight, chlorophyll ´a´) located on an artificial substratum (acetate) of four different polluted sites of the lower parts of the Luján River, Buenos Aires province, was studied. Samplings were conducted nearly monthly, from January to October 1999. Because of the discontinuity on the water level, caused by the Gobernador Arias stream which discharges a great amount of water from the Paraná River, numerical analyses (correlations and multiple linear regressions) were separately done for stations located up (E1 and E2) and downstream (E3 and E4) of the river outlet. Lakatos and autotrophic indexes were used to characterize the periphyton. Physical and chemical variables of the water showed that the Luján River presented signs of pollution, alternating periods of poorer and better water quality. Some of the variables exceeded the allowed limits for human use and aquatic life protection. E1 and E4 showed periods of very low water quality. E1 was likely to be affected by urban pollution from the upper stretch of the river and E4 by the simultaneous action of the Claro stream and the water reflux produced by the relief channel of the Reconquista River. The different fractions of periphytic mass were less variable in E1 and E2 than in E3 and E4, where the fluctuations in the hydrometric level would represent the main regulating factor for the periphyton. The values of the Lakatos indexes regarding dry weight, showed a gradual increase in community mass with time. The recorded types resulting from the percentage of ashes were generally inorganic-organic, with prevalence of the inorganic type in E2. According to the percentage of chlorophyll ´a´, the hetero-autotrophic type predominated in the community, with heterotrophic types occasionally observed. Autotrophic index values were usually greater than 100 due to the high concentrations of organic matter in the stream which, in turn, supported a larger biomass of heterotrophs and detritus. The results indicated that the Luján River has a high concentration of inorganic solids, enriched with organic matter. According to the results of multiple regression analyses, biomass variables were mainly explained by nutrients.

Palabras clave : Biofilm; Dry weight; Ash-free dry weight; Chlorophyll ´a´; Artificial substrata; Urban polluted rivers; Argentine.

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