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