Formation of the Salto Caxias Reservoir (PR) – an approach on the eutrophication process

RIBEIRO^1,2, L.H.L.; BRANDIMARTE^2,3 A.L. & KISHI¹, R.T.

¹ Departamento de Meio Ambiente, Instituto de Tecnologia para o Desenvolvimento – LACTEC Centro Politécnico da UFPR, Curitiba, Paraná, Brasil. C. P. 19067, CEP 81531-990. e-mail: luiza@lactec.org.br; regina.kishi@lactec.org.br

²Programa de Pós-Graduação em Ciência Ambiental da Universidade de São Paulo-PROCAM. ³Departamento de Ecologia, Instituto de Biociências da Universidade de São Paulo, rua do Matão, travessa 14, 321, Cidade Universitária, CEP 05508-900, São Paulo, Brasil, e-mail: anabrand@ib.usp.br

ABSTRACT: This work discusses abiotic and biotic limnological changes after the construction of the Salto Caxias dam in the Iguaçu River (State of Paraná, Brazil). After damming, the main limnological changes were determined by the decomposition of the submerged vegetation, lixiviated soils and contributions from tributaries. There was an immediate depletion of dissolved oxygen, mainly in the hypolimnion, increases in the concentration of phosphorus and nitrogen, and the corresponding increase of phytoplankton biomass (evaluated through chlorophyll-a), especially in the reservoir’s arms. After damming, the reservoir’s characteristics are more lentic with respect to the river that originated the dam and they favored the sedimentation process and the increase of water transparency towards the dam. During the filling phase of the reservoir, the aquatic environment under study went from oligotrophic to mesotrophic conditions, and during the second year after filling, the limnological instability that was observed was still present, although there was a gradual recovery of the surface oxygen levels.

Key-words: reservoirs, eutrophication, limnological variables, damming, filling phase.