Environmental predictors of charophytes in a subtropical reservoir

Aim In this study we check whether three simple environmental factors are good predictors of charophytes occurrence. Methods The Characeae material was sampled two times a year during the years of 2001, 2002 and 2003, over 235 sites distributed along eight rivers located in Itaipu, a large subtropical reservoir. While sampling the biological material, the measurement of environmental descriptors pointed out as the most important variables predicting the occurrence of submerged macrophytes were simultaneously taken. At each sampling site, using a four meter long pipe rake, the presence and absence of Charophytes were recorded, the biological material was sampled and fixed to posterior identification in laboratory following specialized literature, and measurements of the electrical conductivity, Secchi depth and the effective fetch were taken. Results A total of 13 species, belonging to the genus Chara and Nitella, were identified. An increase of the charophytes frequency towards the dam was found, which may reflects the gradient of sedimentation and reduction of the inputs of solids and nutrients, leading to a higher underwater transparency, a suitable condition to the development of submerged macrophytes. The genus Nitella occurred in all rivers and was more frequent than the genus Chara. Regarding the effect of electrical conductivity over the charophytes, the frequency of the genus Chara was found to be affected by this variable, while the effective fetch, variable that indicates wave disturbance, affected genus Nitella. Conclusions The water transparency, related with Secchi depth, was the best predictor for the charophytes occurrence, agreeing with the distribution pattern of other submerged macrophytes of this large subtropical Reservoir. Resumo: Objetivo Neste estudo, verificamos se três simples fatores ambientais são bons preditores de ocorrência de carófitas. Métodos O material de Characeae foi amostrado duas vezes ao ano, durante os anos de 2001, 2002 e 2003, em 235 locais distribuídos ao longo de oito rios localizados em Itaipu, um grande reservatório subtropical. Simultaneamente à coleta do material biológico, medidas de descritores ambientais apontados como os preditores mais importantes para a ocorrência de macrófitas submersas foram aferidos. Em cada local de amostragem, usando um garfo coletor de 4 metros de comprimento, a presença e ausência dos carófitos foi registrada. O material biológico coletado foi fixado para posterior identificação