Eventos de mortandade de peixes associados a florações fitoplanctônicas a lagoa Rodrigo de Freitas: Programa de 10 anos de monitoramento

Abstract

The Rodrigo de Freitas Lagoon (area 2.2km2, mean depth 2.8m) has a Basin of 32km2 and is formed by the rivers Cabeças, dos Macacos and Rainha, which drain areas of Tropical Rain Forest (Mata Atlântica) and urban occupation located in a high density area in the city of Rio de Janeiro. Isolated of the sea for beaches of Ipanema and Leblon, it reflects old problems of sanitation and is in eutrophic state. In consequence, periodic fish kill are registered. The Environmental State Institute (INEA) has been monitoring the phytoplankton community weekly and the abiotic variables twice a week in the entire water column. This periodic monitoring (02/2000 to 12/2010) has searched to supply the measures that allow one better management of this environment. For in such a way one has used the data of the community of phytoplankton as describing biological, beyond the abiotics parameters that had been associates to the fish kill events. Phytoplankton (0.1 × 104 ind.mL-1 to 186 × 104 ind.mL-1) was almost always dominated by Cyanobacteria. The mortality instances shows two response standards regarding phytoplankton structure: one related to rainfall (Pseudoanabaena limnetica was replaced by Prorocentrum cordatum (ex-minimum) dominance), and the other to lack of rain (Synechocystis aquatilis dominance). The set of these data infsidized the implantation of a system of alert, of preliminary form, since January of 2003. The considered system of alert is applied weekly and contributes for of predictability of mortality events and for interventions on the ecosystem.