No abstract

To address daily fluctuations in electricity demands, the quantities of water passing through the turbines of hydropower plants can vary significantly (up to fourfold) during a 24-h cycle. This study evaluates the effects of hourly variations in water discharges on the limnological conditions observed in two below-dam river stretches. The study reservoirs, Capivara and Taquaruçu, are the 9th and 10th reservoirs in a cascade of dams in the Paranapanema River in south-east Brazil. The reservoirs exhibit different trophic conditions, water retention times, thermal regimes and spillway positions. Capivara Reservoir is deeper, meso-eutrophic, with a high water retention time and hypolimnetic discharges (32 m) varying between 500 and 1400 m 3 s )1 . In contrast, Taquaruçu Reservoir is relatively shallow, oligo-mesotrophic, and has a low retention time, with water discharges varying between 500 and 2000 m 3 s )1 . Its turbine water intake zone also is more superficial (7 m). For two periods of the year, winter and summer, profiles of limnological measurements were developed in the lacustrine (above-dam site) zones of the reservoirs, as well as in the downstream river stretches (below-dam site). In both cases, the sampling was carried out at 4-h intervals over a complete nictemeral cycle. The results demonstrated that the reservoir operating regime (water discharge variations) promoted significant differences in the conditions of the river below the dams, especially for water velocity, turbidity, and nutrient and suspended solids concentrations. The reservoir physical characteristics, including depth, thermal stratification and outlet structure, are also key factors influencing the limnology and water quality at the below-dam sampling sites. In the case of Capivara Reservoir, for example, the low dissolved oxygen concentration (<5.0 mg L )1 ) in its bottom water layer was transferred to the downstream river stretches during the summer. These study results demonstrated that it is important to continue such investigations as a means of verifying whether or not these high-amplitude ⁄ low-frequency variations could negatively affect the downstream river biota.

O Rio Tietê (SP) recebe grande parte dos efluentes orgânicos da região metropolitana de São Paulo sendo que o reservatório de Barra Bonita, a mais de 200 km, retém e recicla grande parte desta carga de poluentes. Este trabalho estudou atributos ecológicos da comunidade de zooplâncton (Rotifera, Cladocera e Copepoda), amostrada no trecho entre a desembocadurado citado rio com o reservatório. Foram realizadas coletas mensais entre abril de 2007/fevereiro de 2008.A hipótese testada foi que a comunidade de zooplâncton suporta o forte impacto da poluição, assemelhando-se quali--quantitativamente com outros compartimentos longitudinais do reservatório (intermediário e lacustre sensu Thornton)e outros reservatórios da bacia do alto Rio Paraná. Em termos hidrológicos, o reservatório apresentou uma variação típicade bacia de acumulação, com ampla variação da cota altimétrica sazonal e maior vazão no período chuvoso, influenciado pelo regime pluviométrico, que indicaram relações de efeito sobre a assembleia zooplanctônica. Foram registradas 24 espécies, entre as quais 12 de Rotifera, 8 de Cladocera e 4 de Copepoda. Dados apresentados indicam que a hipótese formulada deve ser rejeitada, pois as tendências de variação dos atributos ecológicos da comunidade de zooplâncton não foram regulares, com valores de abundância relativamente elevados para um ambiente lótico em determinados períodose baixa abundância ou ausência de organismos em outros. Pode-se inferir que essa situação pode ser reflexo das cargaspoluidoras que induzem a baixa concentração de oxigênio dissolvido (> 4mg.l-1) em certos períodos, sendo a comunidadede zooplâncton bastante afetada.

Cite as: Debastiani Júnior, J.R. et al. Fluvial lateral environments in Río de La Plata basin: effects of hydropower damming and eutrophication. Acta Limnologica Brasiliensia, 2016, vol. 28, e26. Abstract: Aim: Identify large-scale limnological patterns in lateral water bodies of Río de La Plata Basin, considering the influence of river damming and urban conglomerates. Methods: Samplings were performed in a broad spatial scale (along 16 latitude degrees) during two seasonal periods (23 sites in summer and 20 sites in winter) for measurements of physical and chemical variables, chlorophyll a and periphyton biomass. Results: Geographical distance between sites was significantly correlated with the environmental dissimilarity (Euclidean distance). Reservoir and floodplain associated sites exhibited lower phosphorus concentration. Eutrophic conditions were higher in sites close to urban areas and regions with intensive agriculture and livestock activities, which exhibited higher conductivity, concentration of nitrogen and chlorophyll a. Sites associated to reservoirs had higher periphyton biomass. Inorganic suspended matter was higher in summer whereas organic suspended matter was higher in the winter, due to contrasting rain seasonality in the upper Paraná River sub-basin. No significant correlation between the dissimilarity of the vegetation and the environmental dissimilarity or geographical distance between sites was observed. Conclusions: The limnological conditions in the fluvial lateral habitats in the Río de La Plata basin are highly influenced by reservoirs construction, intensive urban occupation and rain seasonality.