Data of Dissertation
Author: Patrícia Domingos.
Title: Dominance of cyanobacteria producing microcystins in Jacarepaguá Lagoon, RJ
Year: 2001. Full text (in Portuguese)
Abstract
The phytoplankton community and the occurrence of toxic cyanobacterial blooms in Jacarepaguá lagoon, Rio de Janeiro, were studied in field and in laboratory. This is a shallow brackish lagoon (0 to 10S) and has been receiving domestic and industrial waste for the two past decades, becoming hypereutrophic (136µg.L-1) annual average of chlorophyll a). A study of annual cycle was made (08/96 to 09/97) and the samples were collected each two weeks in three stations. From the begin of the study until the end of spring (11/96) the phytoplankton was dominated by green algae, specially Chlorocoecalcs (61%) being replaced by cyanobacteria (87%), specially Microcystis aeruginosa, the dominant species until the end of studies. The green algae biomass was positively related with nitrate (r= 0.72) and phosphorus concentration (r= 0.55), and with the deep meter (r= 0.90). The correlation was negative with salinity (r= -0.41), temperature (r= -0.31) and ammonium concentration (r= -0.33). The cyanobacteria biomass was directly related to salinity (r=0.59) and ammonium concentration (r=0.42) and indirectly to water transparence (r= -0.40) and temperature (r= -0.30). The HPLC analysis showed the presence or microcrocystins (MC), hepatotoxic cyclic heptapeptides, in the séston samples (0.8 to 979.2 µg.L-1). After the beginning of M.aeruginosa, but not dissolved in the water. The M.aeruginosa biomass, séston MC concentration and cell quota of microcystins (MC/cell of M. aeruginosa) were higher in station 3(Arroio Pavuna) where the waste input is greater. The success of M. aeruginosa in the lagoon was related to salinity (r= 0.58) and ammonium concentration (r=0.41). The variation of salinity was important to explain the development of cyanobacteria in this water system. The experiments in different salinity conditions (0S, 2S, 5S and 10S) with M.aeruginosa (NPLJ_37) growth and microcystins production reveled that salinity has not favored the cyanobacteria. The M.aeruginosa culture with and without Eichhornia crassipes, abundant macrophyte in the lagoon, showing the risk of M.aeruginosa blooms to the environment, since these intermediate values are the most frequent. The constant salinity variations in this lagoon could contribute to increase the hepatotoxic M.aeruginosa biomass, and to increase the microcystins concentration, with consequences for fishing and pleasure activities in this environment.
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