A series of eleven reservoirs was constructed in the Paranapanema River, southeast Brazil, for hydropower production. The phytoplankton structure and its relations with the environmental variables were studied in two of these reservoirs: a large upstream located storage system (high water retention time) and a small run-of-river system (short water retention time). The samples were collected quarterly for two consecutive years, at four sampling stations in each reservoir. Higher phytoplankton richness was observed in the semi-lotic compartments. Higher values of diversities were observed in the upper region of the run-of-river reservoir, under the influence of the larger storage reservoir discharges, and lower values were observed in deeper layers of this same reservoir. The pronounced variation on seasonal rain precipitation and operational water releases, retention time and quota had major influence in the phytoplankton assemblages. The influence of other environmental variables was also indicated by a canonical correlation analysis. Chlamydophyceae, Dinophyceae, Zygnemaphyceae, Chrysophyceae, Chlorophyceae, Bacillariophyceae and Cyanobacteria were positively correlated with higher transparency and depth; Euglenophyceae with temperature and Cryptophyceae with total phosphorus, dissolved oxygen, conductivity, turbidity, total nitrogen and total suspended solids. The influence of the storage reservoir on the phytoplankton of the downstream run-of-river reservoir was more evident in the dry period. During the rainy period the lateral tributaries effects seems to have a higher influence, especially on the smaller studied reservoir.

-The effects of temperature on the life table, and of seston quality on the individual growth and reproduction of cladocerans from a tropical lake were tested in the laboratory. Life-table experiments were carried out at 17 xC, 23 xC, and 27 xC. Growth bioassays tested the influence of natural seston fractions, separated by net filtration, on cladocerans. The treatments were: (1) total seston plus Scenedesmus spinosus (1 mg C.L x1 ), (2) seston j 36 mm, and (3) seston > 36 mm. Phytoplankton composition, density, and biomass were evaluated during growth experiments, together with sestonic carbon, nitrogen, and phosphorus concentrations. The intrinsic rates of natural increase were higher for Moina micrura and Daphnia ambigua at 27 xC compared to 17 xC. The age at first reproduction of both species was delayed at 17 xC. Growth rates and fecundity of M. micrura were higher in the seston fraction j 36 mm than in the fraction > 36 mm. Higher growth rates and fecundity of Moina minuta were observed in the seston enriched with the green alga in comparison to the seston j 36 mm and > 36 mm. Bosmina longirostris was unable to reproduce at 17 xC and to grow in the seston > 36 mm in one experiment. High densities and/or biomass of large colonial and filamentous algae present in the larger seston fraction could have contributed to reduce growth and reproduction. Episodes of food-quantity limitation may occur, but there was no evidence of mineral limitation, although seston C : P and C : N ratios were always above the limiting values assumed for temperate water bodies. The C : P and C : N ratios are highly influenced by carbon that originates primarily from resuspended detritus from the lake.

Changes in richness, diversity, evenness and abundance of phytoplankton in relation to environmental variables and tributary entrances were studied along 30 km of the Paraná River downstream Itaipu Reservoir. A high number of taxa was found, 315. The Paraná River differed from the tributaries Iguaçu River and Monday River. The phytoplankton and limnological characteristics of the Paraná River changed after the entrance of these tributaries. Higher values of richness and alpha diversity of phytoplankton were found in the two tributary rivers, which also produced an increase in the corresponding mean values in the Paraná River. Higher values of total abundance and lower values of evenness were found at the dam site with typical lentic conditions. The assemblages of the two tributary rivers were homogeneous. Bellow dam the phytoplankton exhibited a decrease in abundance and an increase in evenness. Water transparency, water flow, nutrients and turbidity were the main indicators of the system spatial heterogeneity. Several species were correlated with silicate, redox potential and/or water temperature. Reservoir conditions promote conspicuous differences in the phytoplankton of the Paraná River. The downstream reorganization of the community, with a sharp decrease in abundance, is positively influenced by tributary rivers in terms of richness and diversity.

Este trabalho foi realizado na UHE Americana, pertencente à Companhia Paulista de Força e Luz, e faz parte de um projeto de pesquisa e desenvolvimento realizado em conjunto com a Faculdade de Ciências Agronômicas - UNESP, de Botucatu. As amostragens de água foram realizadas nos meses de fevereiro, abril, junho e outubro de 2004. As características analisadas foram: temperatura da água, pH, oxigênio dissolvido, condutividade, nitrogênio total, nitrito, nitrato, amônia, fósforo total, fosfato, fosfato inorgânico, juntamente com análise qualitativa e quantitativa da comunidade fitoplanctônica e a toxicidade. O reservatório apresentou valores elevados de fósforo total, variando de 18 a 509 µg L-1; fosfato, de 4 a 463 µg L-1; nitrogênio total, de 0,99 a 17,25 mg L-1; e nitrato, de 0,26 a 15,29 mg L-1. Para a comunidade fitoplanctônica foram encontrados 103 táxons em todo o período amostrado; a maior riqueza foi encontrada no ponto P06, e a maior pobreza de táxons, nos pontos localizadas no corpo central do reservatório (P02, P03, P04 e P05). A maior concentração de cianofícea ocorreu em abril de 2004: 5.375.175 ind. L-1. As espécies que apresentaram as maiores densidades foram Microcystis aeruginosa, Anabaena spiroides, Microcystis sp. e Pseudoanabaena mucicola; a maior densidade foi apresentada por Anabaena spiroides, com 4.178.084 ind. L-1. Nos meses de junho e outubro a classe Cryptophyceae teve uma grande contribuição para a densidade total. Apesar da grande densidade de cianobactérias, os valores de toxicidade ficaram abaixo do limite permitido pela Portaria nº 1.469.

No abstract

We developed and validated a Planktonic Index of Biotic Integrity for subtropical reservoirs to assess their ecosystem health. For this purpose, we analyzed the phytoplankton and zooplankton communities and determined reservoir trophic status in the Paranapanema River system (Southeast Brazil). Eleven dams were constructed in the main course of this river to supply hydropower plants. Three of the reservoirs are accumulation systems (i.e. with high water retention times), whereas the others are run-of-the-river systems. For the study the three larger reservoirs (Jurumirim, Chavantes and Capivara) were selected. Physical, chemical, and biological (phytoplankton and zooplankton) data were obtained in two sampling campaigns carried out in March (wet season) and October (dry season) of 2011. For each reservoir we sampled six stations, arranged on a gradient established between the lotic (Paranapanema River entrance) and lentic (dam) areas. According to the Trophic State Index for tropical/subtropical reservoirs, the sampling stations were categorized between ultraoligotrophic and mesotrophic. Four metrics achieved significant discrimination (out of a set of 20 candidate metrics). The individual metric scores were summed to provide a Planktonic Index of Biotic Integrity score, which ranged as Mesotrophic (4-9), Oligotrophic (10-14) and Ultraoligotrophic (15-20), corresponding to the classification of fair, good and excellent, respectively. Following the longitudinal sequence, Jurumirim was classified as Oligotophic (Good) and both Chavantes and Capivara as Ultraoligotrophic (Excellent). This study demonstrated that the Planktonic Index of Biotic Integrity is a potential tool for monitoring large subtropical reservoirs, as planktonic organisms are sensitive to environmental changes and this index integrates distinct temporal and spatial scales.

Aim: Bioassays were carried out seasonally to evaluate individual growth and reproduction of cladocerans, from a marginal lake, with the addition of nitrogen (N), phosphorus (P), and both N and P to natural seston; Methods: Cohorts originated from cultivated females were submitted to the following treatments: 1) lake seston, 2) lake seston + P, 3) lake seston + N, and 4) lake seston + NP; Results: The sestonic C:P and C:N molar ratios were always high and limiting, according to threshold ratios estimated for temperate lakes. P addition to seston enhanced the growth rates of one species, D. birgei. A significant higher growth rate of B. longirostris was found in the seston enriched with N compared to natural seston, as well as a higher fecundity of M. minuta. The fecundity of D. birgei was significantly higher in the seston enriched with both N and P. C, N, and P body content of cladocerans was similar to that of temperate counterparts; Conclusion: Energy limitation related to carbon content or food quality seems to be most important in controlling cladocerans' populations in the lake than food mineral content.Resumo: Objetivo: Foram realizados experimentos para avaliar o crescimento individual e a reprodução de cladóceros de uma lagoa marginal com a adição de nitrogênio (N), fósforo (P) e fósforo e nitrogênio juntos ao séston natural; Métodos: Os experimentos foram realizados sazonalmente. Coortes originadas de fêmeas cultivadas foram submetidas aos seguintes tratamentos: 1) séston do lago, 2) séston do lago + P, 3) séston do lago + N e 4) séston do lago + NP; Resultados: As razões molares C:P e C:N do séston estavam sempre altas, de acordo com razões estimadas para lagos temperados. A adição de P ao séston aumentou somente o crescimento de D. birgei. No entanto, a fecundidade de B. longirostris foi significativamente maior no tratamento do séston enriquecido com N comparado ao séston sem adições, assim como a fecundidade de M. minuta. A fecundidade de D. birgei foi significantemente maior no séston enriquecido com N e P. O conteúdo corporal de C, N e P dos cladóceros foi similar ao encontrado para cladóceros de região temperada; Conclusão: A limitação por energia relacionada ao conteúdo de carbono ou à qualidade do alimento parece ser mais importante no controle das populações de cladóceros no lago comparado ao conteúdo mineral do alimento.Palavras-chave: limitação mineral, nitrogênio, fósforo, séston, cladóceros tropicais.