Fitoplancton de ambientes inundables del rio Parana (Argentina) : estudio comparativo entre areas libres y vegetadas

Le phytoplancton a été étudié dans deux mares (Llanta et Perdida) et dans un marais (Choui) sur des îles du rio Parana (27° 30°S, 58° 55 O). Des échantillons ont été prélevés dans la végétation des rives et dans les eaux libres en période de crue et d'étiage entre décembre 1981 et février 1983. La densité et la diversité spécifique ont été analysées en fonction des variables de l'environnement. En période d'étiage, la diversité la plus faible et la densité la plus forte (7706 ind/ml) ont été trouvées dans le marais à #Panicum grumosum, avec dominance de l'Euglénophycée #Trachelomonas volvocina. Dans les mares, les plus fortes densités ont été relevées dans la mare Llanta dans les zones à #Eichhornia azurea et #Salvinia sp., et dans la mare Perdida, dans les herbiers à #Polygonum acuminatum

Efecto de las fluctuaciones del nivel hidrométrico sobre el fitoplancton en tres lagunas isleñas en el área de la confluencia de los ríos Paraná y Paraguay

The phytoplankton of three island ponds (Los Pájaros, Catay and Turbia) (27°25’S; 58°45’W) in the begening of Paraná river floodplain were studied. These ponds are periodically flooded by the river. Catay pond was in pennanent contact with the riverwhile the other two were flooded during high water periods.Sampling was carried out during 1978-1980. Cell counts were madeby the U termohl method. Population density and diversity and were analyzed. Cell density were comparatively highest (1733, 2084 and 1028 ind. ml4 in Pájaros, Catay and Turbiaponds, respectively) either when hydrometric level was slowly increasing or after small flood phases. On the contrary, cell density were lowest in coincidence with strong flooding phases (83,73 and 57 ind. mi'1, respectively). Catay pond, the one which is in pennanent contact with the river showed highest both population density and diversity. During high water periods strong similarity ainong three ponds were observed.In Pájaros and Catay ponds Chlorophyceae (Monoraphidium, Schroederia and Scenedesmus), Ciyptophyceae (Cryp tomonas spp.) and Diatomophyceae A ulacoseira granúlala) were dominant. In the Turbia pond Euglenophyceae (Traclielomonasvolvocina) and Cryptophyceae (Cryptomonas spp.) were dominant.Nannoplankton represented between 60 and 90% of the total in all the studied ponds..The phytoplankton of three island ponds (Los Pájaros, Catay and Turbia) (27°25’S; 58°45’W) in the begening of Paraná river floodplain were studied. These ponds are periodically flooded by the river. Catay pond was in pennanent contact with the riverwhile the other two were flooded during high water periods.Sampling was carried out during 1978-1980. Cell counts were madeby the U termohl method. Population density and diversity and were analyzed. Cell density were comparatively highest (1733, 2084 and 1028 ind. ml4 in Pájaros, Catay and Turbiaponds, respectively) either when hydrometric level was slowly increasing or after small flood phases. On the contrary, cell density were lowest in coincidence with strong flooding phases (83,73 and 57 ind. mi'1, respectively). Catay pond, the one which is in pennanent contact with the river showed highest both population density and diversity. During high water periods strong similarity ainong three ponds were observed.In Pájaros and Catay ponds Chlorophyceae (Monoraphidium, Schroederia and Scenedesmus), Ciyptophyceae (Cryp tomonas spp.) and Diatomophyceae A ulacoseira granúlala) were dominant. In the Turbia pond Euglenophyceae (Traclielomonasvolvocina) and Cryptophyceae (Cryptomonas spp.) were dominant.Nannoplankton represented between 60 and 90% of the total in all the studied ponds

Aspectos ecológicos de la ficoflora de ambientes acuáticos del Chaco Oriental (Argentina)

The present study describes the al gal flora of some streams and tropical swamps ("esteros") settled in the Eastern Chaco between the Pilcomayo (25°15'S; 57°45'W) and Amores (28°15'S; 59°30'W) rivera towards the Paraguay-Paraná axis. Samples taken during 1984 at different hydrometric levels within the annual hydrologic re gime, were compared. The quali and quantitative study of the phytoplankton was carried out, as well as the periphytic flora from natural substrates with addition of SEM analyses. Counts of phytoplankton were done by the Utermohl method. Phytoplankton density was low during the high water period (between 15 and 280 ind.ml-1), and high species richness were found. During the low water period the phytoplankton density ranged from 20 to 1746 ind.ml-1. The highest density was recorded in highly salinitized water bodies with blooms of halophilous species (Glenodinium balticum and Protoperidinium achromaticum).  In response to high salinity and alkalinity diatoms such as Nitzschia acicularis var. closterioides, Surirella striatula, Campylodiscus clypeus and Bacillaria paradoxa were found in the phytoplankton. Besides, Audouinella sp. (Rhodophyta) and Enteromorpha sp. (Chlorophyta) were observed in the periphyton. In the tropical swamps the phytoplankton density ranged from 22 to 525 ind.ml-1 with high species number of Euglenophyta. Acidity indicators species (within Chrysophyceae, Xanthophyceae and Diatomophyceae) were recorded in the periphyton. Thus, local populations showed strong differences with respect to other regional waterbodies of the Northeastem of Argentina.The present study describes the al gal flora of some streams and tropical swamps ("esteros") settled in the Eastern Chaco between the Pilcomayo (25°15'S; 57°45'W) and Amores (28°15'S; 59°30'W) rivera towards the Paraguay-Paraná axis. Samples taken during 1984 at different hydrometric levels within the annual hydrologic re gime, were compared. The quali and quantitative study of the phytoplankton was carried out, as well as the periphytic flora from natural substrates with addition of SEM analyses. Counts of phytoplankton were done by the Utermohl method. Phytoplankton density was low during the high water period (between 15 and 280 ind.ml-1), and high species richness were found. During the low water period the phytoplankton density ranged from 20 to 1746 ind.ml-1. The highest density was recorded in highly salinitized water bodies with blooms of halophilous species (Glenodinium balticum and Protoperidinium achromaticum).  In response to high salinity and alkalinity diatoms such as Nitzschia acicularis var. closterioides, Surirella striatula, Campylodiscus clypeus and Bacillaria paradoxa were found in the phytoplankton. Besides, Audouinella sp. (Rhodophyta) and Enteromorpha sp. (Chlorophyta) were observed in the periphyton. In the tropical swamps the phytoplankton density ranged from 22 to 525 ind.ml-1 with high species number of Euglenophyta. Acidity indicators species (within Chrysophyceae, Xanthophyceae and Diatomophyceae) were recorded in the periphyton. Thus, local populations showed strong differences with respect to other regional waterbodies of the Northeastem of Argentina

Spatio-temporal variability in underwater light climate in a turbid river-floodplain system. Driving factors and estimation using Secchi disc

The underwater light climate has important effects on primary producers. The aim of this research was to evaluate its variability in a turbid river-floodplain system. Photosynthetically active radiation (PAR) was measured in the Middle Paraná River during different hydrological phases to (a) analyse the photosynthetically active radiation attenuation coefficient (k) and euphotic depth (Zeu) as well as their associations with optically active components and (b) develop and evaluate indices and regression models based on Secchi disc (SD) measurements to estimate k and Zeu. Values of k were higher in the fluvial system than in the floodplain and during low-water stage than high-water stage. Particulate components controlled the light climate variability. Chromophoric dissolved organic matter and chlorophyll-a had significant effects during floods. The estimation of k and Zeu was sensitive to temporal but not to spatial variations. The highest prediction accuracy was observed when using specific non-linear regressions for each hydrological phase, especially for Zeu estimation (low stage: k = 1.76 × SD−0.80, Zeu = 2.62 × 1/SD−0.80; high stage: k = 2.04 × SD−0.53, Zeu = 2.26 × 1/SD−0.53). The indices k × SD and Zeu/SD were significantly different from those proposed for clear water environments. It is concluded that temporal variations should be considered when estimating k and Zeu in turbid river-floodplain systems because of the temporal heterogeneity in optically active components. Considering that ecological implication of the light climate depends on Zeu:depth ratio, we propose to estimate Zeu instead of k. Finally, indices proposed for clear water environments are not recommended to be applied to turbid environments.Fil: Mayora, Gisela Paola. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Devercelli, Melina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentin