Modelling the risk of mortality of Corbicula fluminea exposta a diferentes condicoes de turbidez

The provision of sediment in rivers, due to erosion processes that occur in the environment, consists of a major source of pollution and alteration of the physicochemical conditions of water resources. In addition, the increase in water turbidity may cause siltation, dramatically impacting aquatic communities. Specifically considering the bivalve Corbicula fluminea (Muller, 1774), the aim of this study was to analyse the effect of exposure to different turbidity conditions of sediments, as a risk factor for the animals. For this purpose, a docking device was designed to ensure water circulation in a closed system and to maintain the desired levels of turbidity. Although C. fluminea can generally tolerate environmental changes in aquatic systems, an intolerance to high turbidity levels was experimentally observed, expressed by the mortality rate of the animals when exposed to conditions above 150 nephelometric turbidity units (NTU). This value was similar to the one recorded at study sites in the rivers Pardo (Serrana-SP-Brazil) and Mogi Guacu (Porto Ferreira-SP-Brazil) during the rainy season. Using a logistic regression model, the experimental results were analysed and the observed mortality rates indicate that the exposure of the animals to turbidity levels above 150 nephelometric turbidity units (NTU), for periods longer than 120 hours, may be considered a probable cause of mortality for the species. Keywords: biodiversity, bivalve, erosion, watershed, logistic regression. A disponibilizacao de sedimentos nos cursos d'agua, em funcao dos processos erosivos que ocorrem no entorno, constitui-se e uma das principais fontes de poluicao e alteracao das condicoes fisico-quimicas dos recursos hidricos. Alem disso, o aumento da turbidez da agua pode causar assoreamento, impactando drasticamente as comunidades aquaticas. Especificamente para o bivalve Corbicula fluminea (MULLER, 1774), este estudo teve por objetivo analisar o efeito da exposicao a diferentes condicoes de turbidez, como fator de risco para os animals. Para esta finalidade, um dispositivo de acoplamento foi concebido para assegurar a circulacao da agua, em um sistema fechado mantendo os niveis desejados de turbidez. Embora C. fluminea possa tolerar mudancas ambientais em sistemas aquaticos, foi observadao experimentalmente, uma intolerancia a turbidez acima de 150 unidades nefelometricas de turbidez (NTU), um valor proximo ao registrado em pontos de estudo nos rios Pardo (Serrana-SP-Brasil) e Mogi