TOXIC CYANOBACTERIAL BLOOMS IN AN EUTROPHICATED COASTAL LAGOON IN RIO DE JANEIRO, BRAZIL: EFFECTS ON HUMAN HEALTH.

Abstract

revista vol 13 nº 2.indd

The Jacarepaguá Basin, Rio de Janeiro, Brazil has over the last four decades undergone a disordered process of urban and industrial growth with direct consequences on water quality and incidence of cyanobacterial blooms in the Jacarepaguá Lagoon Complex (JLC). The present study combines data aiming to evaluate water quality in Jacarepaguá Lagoon (JL) from monitoring of physical variables (pH, water transparency, temperature), chemical variables (salinity, dissolved oxygen, chlorophyll), the planktonic community, and the concentration of microcystins in fish from the region. The data herein presented were divided into three periods according to seasonal cycles: PI (aug/96 to sep/97), PII (jan/99 to nov/99), and PIII (feb/07 to jan/08). Dominance by cyanobacteria characterized most of the study period, interspersed with sudden peaks (e.g. during PII and PIII) of high diversity of phytoplankton. Phytoplanktonic peaks were represented by Chlorophyta, diatoms, Prasinophyta and Criptophyta. Interestingly, the events observed in 1999 repeated almost 10 years later, suggesting roughly seasonal community structure dynamism in the JLC. Disappearance of the bloom coincided with the lowest recorded water temperatures, suggesting that temperature is an important factor in the observed dynamics. The JL had a high abundance of zooplankton, yet species diversity was relatively low. Concentrations of microcystins found in muscles of fish from JL often contained values above the levels recommended by OMS for human consumption.