Assessing the effect of abiotic variables and zooplankton on picocyanobacterial dominance in two tropical mesotrophic reservoirs by means of evolutionary computation.

Evolutionary computation has been applied to predict the occurrence of massive cyanobacteria proliferations; in the present study, this tool was further used to explore the factors responsible for maintaining picocyanobacterial dominance. Aiming to increase the understanding of factors that promote dominance of picocyanobacteria in tropical reservoirs, we chose two reservoirs used for water supplies located in different regions of Brazil and subjected to climate changes such as warmer winters that intensify water column stratification and prolonged dry seasons that cause water level decreases. This study focused on the diagnosis of the relationships among picocyanobacteria (1-2 µm), zooplankton and environmental variables using evolutionary computation. The integrated data analysis performed here was very successful in elucidating the dynamics of picocyanobacterial density variation influenced by both abiotic and biotic factors by the modeling approach. Relative water column stability - RWCS and electrical conductivity were highlighted as the most important environmental drivers for picocyanobacterial peaks. Hybrid Evolutionary Analysis (HEA) models for the two reservoirs indicated for the first time in the literature that rotifers, small-sized cladocerans and copepods (mainly nauplii) can directly or indirectly control picocyanobacteria in tropical mesotrophic reservoirs, depending on RWCS conditions and electrical conductivity. However, this control is modulated by pH, water transparency and water temperature thresholds.

Micronuclei monitoring of fishes from Lake Paranoá, under influence of sewage treatment plant discharges.

Fish micronuclei tests (MN) were used to evaluate the ability of wastewater from two municipal sewage treatment plants that empty into Lake Paranoá to cause genetic damage. There were no significant differences in the frequencies of micronuclei between the control and hypertrophic areas. In contrast, cyclophosphamide and mitomycin C, used to test the sensitivity of the biological assay, significantly increased the micronuclei counts in Tilapia rendalli, Oreochromis niloticus and Cyprinus carpio, T. rendalli was the most sensitive specie to both clastogens and C. carpio, the most resistant.

Comparative study of the zooplankton composition of six lacustrine ecosystems in central Brazil during the dry season.

Zooplankton community from six lacustrine ecosystems located in Federal District (Central Brazil) was studied based on samples collected during the dry season (July to September). A total of 71 taxa were recorded: 44 rotifers, 17 cladocerans and 10 copepods. The highest number of zooplankton species was recorded in oligotrophic Bonita Pond (32 species) and the lowest number in hypertrophic waste stabilisation ponds (7 species). This tendency of decreasing the diversity with increasing trophic level was consistent with a cluster analysis of the samples based on Sorensen index of similarity. From the overall similarity dendrogram, two groups of ecosystems were distinguished: one containing the natural ponds Bonita and Formosa and the other comprising the reservoirs Santa Maria, Descoberto and Paranoá. The role of morphometric features in determining the zooplankton community in such lacustrine ecosystems was also discussed.