Longitudinal gradient in limnological variables in the Upper Paraná River: A brief description and the importance of undammed tributaries

Natalia Fernanda Santana, Larissa Strictar Pereira, Maria do Carmo Roberto, Sue Ellen Amaral Gomes, Roger Paulo Mormul


Abstract: Aim: Describe the limnological pattern in a longitudinal gradient in the Paraná River, a highly dammed river, in a stretch localized between two dams, but rich in undammed tributaries. Methods: Twelve transects in the longitudinal gradient of the Paraná River were sampled, with the first transect being placed right after Porto Primavera dam, and the last one in the lentic region of the Itaipu dam. In each of these transects, water transparency, electrical conductivity, pH, total nitrogen and total phosphorous were analyzed. Results: In those regions nearer Porto Primavera dam it was observed high values of water transparency and low values of nitrogen and phosphorous. The values of water transparency decreased and the values of nitrogen and phosphorous increased as the distance from Porto Primavera dam increased and new tributaries connect to the Paraná River, with the sites farer from Porto Primavera dam presenting values similar to those prior its construction. Conclusions: Increase in the nutrients concentration and changes in water quality are probably due to the presence of the undammed tributaries that, as they originate in different river basins, are able to contribute to the Paraná River in distinct manners. Results presented here are an indicative of the fundamental importance of undammed tributaries in mitigating damming negative impacts in extremely dammed rivers and highlight the importance of keeping such tributaries free of dams.



reservoir impact; oligotrophication; Porto Primavera; nutrient retention; floodplain.

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