Morphological and molecular characterization of cyanobacteria from a Brazilian facultative wastewater stabilization pond and evaluation of microcystin production

The cyanobacterial population in the Cajati waste stabilization pond system (WSP) from São Paulo State, Brazil was assessed by cell isolation and direct microscope counting techniques. Ten strains, belonging to five genera (Synechococcus, Merismopedia, Leptolyngbya, Limnothrix, and Nostoc), were isolated and identified by morphological and molecular analyses. Morphological identification of the isolated strains was congruent with their phylogenetic analyses based on 16S rDNA gene sequences. Six cyanobacterial genera (Synechocystis, Aphanocapsa, Merismopedia, Lyngbya, Phormidium, and Pseudanabaena) were identified by direct microscope inspection. Both techniques were complementary, since, of the six genera identified by direct microscopic inspection, only Merismopedia was isolated, and the four other isolated genera were not detected by direct inspection. Direct microscope counting of preserved cells showed that cyanobacteria were the dominant members (>90%) of the phytoplankton community during both periods evaluated (summer and autumn). ELISA tests specific for hepatotoxic microcystins gave positive results for six strains (Synechococcus CENA108, Merismopedia CENA106, Leptolyngbya CENA103, Leptolyngbya CENA112, Limnothrix CENA109, and Limnothrix CENA110), and for wastewater samples collected from raw influent (3.70 μg microcystins/l) and treated effluent (3.74 μg microcystins/l) in summer. Our findings indicate that toxic cyanobacteria in WSP systems are of concern, since the treated effluent containing cyanotoxins will be discharged into rivers, irrigation channels, estuaries, or reservoirs, and can affect human and animal health.     

Temporal changes in the phytoplankton community structure in a tropical and eutrophic reservoir (Barra Bonita, S.P.--Brazil)

A study of the temporal changes in the phytoplankton communitystructure in the eutrophic Barra Bonita Reservoir (SãoPaulo State, Brazil) was carried out during 30 days (sampleswere taken daily for 10 days and, thereafter, on every otherday) in two distinct seasonal periods (dry and rainy seasons).Monthly sampling occurred in the period July 1993 to June 1994.One hundred and thirty-one taxa were registered. A greater diversity(112 taxa) was observed in winter than in summer (79 taxa).In the monthly analysis, 90 taxa were identified. The highestvalues for species diversity and richness were observed in July1993 and the lowest in April 1994. The phytoplankton dynamicsin this system are apparently dominated by competitive exclusionand disturbance. Within theseasonal cycle, the phytoplanktoncommunity structure was determined by underwater light availability,mixing by wind, precipitation and the consequent loss of Cyanophyceaebiomass in the upper waters by spillage, and nutrient (principallyphosphorus) inputs from anthropogenic sources. The environmentalvariability in this polymictic system may be favouring a phytoplanktoncommunity in equilibrium, with dominance alterations of Bacillariophyceaebiomass (Aulacoseira granulata), R-strategists, and Cyanophyceaebiomass (Microcystis aeruginosa), S-strategists. Short periods(i.e. 10 days) in non-equilibrium conditions with increasedspecies diversity and coexistence can perhaps be explained bythe intermediate disturbance hypothesis.     

Short-term changes in the Barra Bonita reservoir (São Paulo, Brazil): emphasis on the phytoplankton communities

We investigated the biomass, primary productivity, species diversity and their controlling factors in the deeper region of the Barra Bonita reservoir (22°29S and 48°34W) in the State of São Paulo, Brazil. To accomplish this, short term changes (days and month) were measured during two periods of the year, winter 1993 and summer 1994. The response of the phytoplankton communities to the variability of the system, taking into account the Intermediate Disturbance Hypothesis (IDH), indicated that the frequency and intensity of the disturbances have a critical influence on the establishment of the communities. In Barra Bonita Reservoir the conditions for mixing in the winter were probably important for maintaining high diversity. On the other hand, in summer, the concentrations of suspended material, the high temperatures, and the greater stability of the water column, were probably responsible for permitting the establishment of Microcystis aeruginosa.     

Temporal variations in phytoplankton primary production in a tropical reservoir (Barra Bonita,SP – Brazil)

Temporal variations of phytoplankton primary production in Barra Bonita Reservoir (22° 29 5 S, 48° 34 W, São Paulo State, Brazil) were evaluated by monthly in situ observations in the period July 1993 to June 1994 and by frequent (every 2 days for 4 weeks) sampling during the dry and colder (July) and wet and warmer (January/February) periods. Highest primary production was observed in April (654 mgC m^–2 h^–1), which also coincided with the period of longest theoretical water retention time. In July, the primary production was the lowest (20 mgC m^–2 h^–1). Nanoplankton production was the highest in October (192 mgC m^–2 h^–1) corresponding to 81% of the total. June represented the period with the lowest share of nanoplankton production (17%, 9 mgC m^–2 h^–1). Nanoplankton was predominant during 8 of the 12 months of observation, representing an average of 41% of the total community primary production. During January/February, most organisms were smaller than 20 m. Microphytoplankton production was higher in the colder and dryer period. The production values found during the periods of intensive measurements were higher in the wet January/February period, with the average value of 135 mgC m^–2 h^–1, while the lowest production values were found in the dry winter (July) when they represented 90 mgC m^–2 h^–1. The cause of the high January values was partially bigger loads of nutrients from the watershed during the high flow, but probably also faster nutrient regeneration at higher temperatures. Barra Bonita primary production is currently three times higher than that observed 15 years ago.     

Survival strategies of some species of the phytoplankton community in the Barra Bonita Reservoir (São Paulo,Brazil)

The dynamics of the phytoplankton community in the Barra Bonita Reservoir (S?o Paulo, Brazil) were studied through daily sampling in the field (integrated samples from the euphotic zone) and microcosm experiments, for two short periods: the winter of 1993 (June 30 to July 10) and the summer of 1994 (January 24 to February 2). The goal of the study was to evaluate and compare the variations in the composition of isolated phytoplankton community which occur over short periods of time. Three series were separated into Erlenmeyer flasks for each study period, with samples from the euphotic zone divided into three portions: total, smaller than 64 μm, and smaller than 20 μm. All of the Erlenmeyer flasks were inclubated in situ at the sampling station. The maximum period of incubation was 10 d. Variations of the community in the euphotic zone were characterised by high diversity and a community in a state of non-equilibrium in winter, without the predominance of any species. In the summer, the community presented a low diversity and a state of equilibrium, with the predominance of Microcystis aeruginosa. The microcosm experiments showed that the confinement of the community in the Erlenmeyer flasks, and therefore in isolation from the physical variability of the ecosystem, especially in relation to the mixing patterns, stimulated the return of the community to the initial phases of succession with the predominance of small species and those which grow rapidly (r-selective or C-strategist). This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of macrophyte leachate on <Emphasis Type="Italic">Anabaena</Emphasis> sp. and <Emphasis Type="Italic">Chlamydomonas moewusii</Emphasis> growth in freshwater tropical ecosystems

This study reports on the effects of dissolved organic matter (DOM) derived from the aquatic macrophyte Pistia stratiotes (collected from a tropical reservoir) on the mixotrophic growth of two phytoplankton species (Chlamydomonas moewusii and Anabaena sp.). The DOM from P. stratiotes had a mainly aliphatic structure, low molecular weight, low cellulose and lignin content and high carbon content. The addition of DOM (5% v/v) significantly decreased the growth rate of Anabaena sp. but increased the chlorophyll a concentration of C. moewusii. Higher light intensity (100 versus 30 µmol m^?2 s^?1) was important for Anabaena sp., increasing its growth rate and chlorophyll content. The use of DOM from P. stratiotes to mitigate cyanobacterial blooms should be further explored in future studies.