Abstract
This study investigated the effect of seasonality on the Cyanobacteria community in two tropical eutrophic reservoirs in northeastern Brazil. Monthly samplings were conducted in the sub-surface of reservoirs. The following abiotic variables were analyzed: apparent color, turbidity, conductivity, alkalinity, calcium, magnesium, sodium, potassium, sulfate, total phosphorous, ammonia, nitrate, nitrite, chlorides, total hardness and chlorophyll-a, according to APHA (2012). Cyanobacteria density was quantified through biomass. Data were analyzed using one-way ANOVA and Redundancy Analysis (RDA). Higher mean values of Cyanobacteria biomass occurred in the dry (9.9mm 3 L -1 ) and rainy (19.0mm 3 L -1 ) season in Jucazinho and Carpina reservoirs, respectively, especially Planktothrix agardhii, Cylindrospermopsis raciborskii and Geiterinema amphibium, which occurred in 100% of the samples. RDA analysis revealed that the variables nitrite, ammonia, conductivity, calcium, sulfate, chlorides and alkalinity influenced most the Cyanobacteria community in both reservoirs. High trophic state index was observed throughout the year. Seasonality affected both biotic and abiotic variables.
Highlights
The occurrence of Cyanobacteria has been observed in various environments, but prevalent in freshwater ecosystems (LEE, 2008)
Environmental conditions are influenced by rainfall events (BORGES et al, 2008, CHELLAPPA et al, 2008), which alter the volume and level of the ecosystem, being especially important to the dynamics of the phytoplankton community (ALMEIDA et al, 2012, DANTAS et al, 2008, 2012)
Data of air temperature and rainfall confirmed the occurrence of two distinct seasons in the regions where the Jucazinho and Carpina reservoirs are located
Summary
The occurrence of Cyanobacteria has been observed in various environments (freshwater, brackish, marine and terrestrial), but prevalent in freshwater ecosystems (LEE, 2008). Temperature has no significant influence on phytoplankton dynamics, due to little variations with values usually high above, the limiting ones to growth, but seasonal patterns of phytoplankton communities cannot be neglected (FIGUEREDO; GIANI, 2009). In these ecosystems, environmental conditions are influenced by rainfall events (BORGES et al, 2008, CHELLAPPA et al, 2008), which alter the volume and level of the ecosystem, being especially important to the dynamics of the phytoplankton community (ALMEIDA et al, 2012, DANTAS et al, 2008, 2012)
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