Limnological comparison of two peridunar ponds in the Doñana National Park (Spain)

The ponds Santa Olalla and Dulce belong to the peridune pond system on the E—W coastline of the Doñana National Park. The water that fills these ponds originates in the groundwater tables of the dunar system, and these ponds also contain rainwater (run-off and drainage). Despite the fact that they are contiguous ponds,which join up during determined periods, they present differences, both in water chemical characteristics and in their phyto- and zooplanktonic communities. Santa Olalla shows conductivity values of 3 to lOmS/cm in the dry period, and of 0.5 to 3mS/cm in the rainy one. Its water is sodium chloride enriched. The pH values vary between 7 and 11. It is a hypereutrophic pond with chlorophyll-a at higher concentration than 100mg/m3 in most of the samples. The phytoplankton community is dominated by Spindina platensis, Anabacnopsis circtdaris, Microcystis aeruginosa, Apha- nothece clathrata and Coelospbaerium kuetzingianum. The zooplankton is dominated by Bracbionus plicatilis, Keratella quadrata, Daphnia magna and Acantbocyclops robustus. Dulce presents a lower salinity (conductivity values between 0.8 and 2.5mS/cm in the dry period and between 0.25 and 1.7 in the rainy one) and althouhg it also has sodic chloride enriched water, the proportion of divalent cations is higher than Santa Olalla. The pH values vary between 6 and 9.5. Macrophyte develop in this pond. The phytoplankton community is dominated by Chroococcus dispersas, Merismopoedia punctata, Aphanocapsa elaebista, Kirchneriella microscópica, Monorapbidium spp and Scenedesmus spp. The zooplankton is dominated by Acantbocyclops robustus and Arctodiaptomus wierzejski.Facultad de Ciencias Naturales y Muse

Algas fitoplanctónicas de ambientes lénticos y lóticos de la cuenca del Río Salado: tolerancia a factores físicos

The objective of this paper was to evaluate relationships between phytoplankton algae density and physical factors such as conductivity and temperature in lentic and lotic environments of Salado River basin. The information was obtained from 352 samples taken in San Miguel del Monte shallow lake, in the seepage Lacombe and in the Salado River (main channel and tributaries). Species with density higher than 4.000 individuals ml-1 were selected: eight cyanobacteria, four chlorophytes, three diatoms and one cryptomonadal. Temperature and conductivity optima and tolerance of species temperature were calculated. The chlorophytes showed highest optima temperature average (18,84 ºC) than the cyanobacteria (17,96 ºC) and diatoms (16,31 ºC). Optima temperature of Cryptomonas pusilla was high (19,86ºC). Diatoms and cryptomonadales showed conductivity optima average (5514 and 5599 μS cm-1) higher than chlorophytes and cyanobacteria (4506 and 3508 μS cm-1). Aphanocapsa delicatissima showed markedly low conductivity optima in the lakes (2002 μS cm-1) respect to the obtained in the Salado River (8989 μS cm-1). It must be emphasized that ranges observed in lotic environments were wider than those in lentic environments. The species optima may be useful for future interpretations of the phytoplankton ecology and also as biological indicator for waterquality assessment in the studied environments.El objetivo de este trabajo fue evaluar las relaciones entre la densidad de algas fitoplanctónicas y factores físicos como la conductividad y la temperatura en ambientes lénticos y lóticos de la cuenca del río Salado. La información se obtuvo de 352 muestras tomadas en la laguna San Miguel del Monte, en la Lacombe y en el río Salado (canal principal y afluentes). Se seleccionaron especies con densidad superior a 4000 individuos ml-1: ocho cianobacterias, cuatro clorofitas, tres diatomeas y una criptomonadal. Se calcularon los valores óptimos de temperatura y conductividad y la tolerancia de la temperatura de la especie. Los clorofitos mostraron un promedio de temperatura óptimo más alto (18,84 ºC) que las cianobacterias (17,96 ºC) y diatomeas (16,31 ºC). La temperatura optima de Cryptomonas pusilla fue alta (19,86ºC). Las diatomeas y criptomonadales mostraron una conductividad promedio óptima (5514 y 5599 μS cm-1) mayor que las clorofitas y cianobacterias (4506 y 3508 μS cm-1). Aphanocapsa delicatissima mostró el óptimo más bajo de conductividad en las lagunas  (2002 μS cm-1) con respecto a los obtenidos en el río Salado (8989 μS cm-1). Se debe enfatizar que los rangos observados en los entornos lóticos fueron más amplios que los de los entornos lénticos. Las especies óptimas pueden ser útiles para futuras interpretaciones de la ecología del fitoplancton y también como indicador biológico para la evaluación de la calidad del agua en los ambientes estudiados

Algas fitoplanctónicas de ambientes lénticos y lóticos de la cuenca del Río Salado: tolerancia a factores físicos

The objective of this paper was to evaluate relationships between phytoplankton algae density and physical factors such as conductivity and temperature in lentic and lotic environments of Salado River basin. The information was obtained from 352 samples taken in San Miguel del Monte shallow lake, in the seepage Lacombe and in the Salado River (main channel and tributaries). Species with density higher than 4.000 individuals ml-1 were selected: eight cyanobacteria, four chlorophytes, three diatoms and one cryptomonadal. Temperature and conductivity optima and tolerance of species temperature were calculated. The chlorophytes showed highest optima temperature average (18,84 ºC) than the cyanobacteria (17,96 ºC) and diatoms (16,31 ºC). Optima temperature of Cryptomonas pusilla was high (19,86ºC). Diatoms and cryptomonadales showed conductivity optima average (5514 and 5599 μS cm-1) higher than chlorophytes and cyanobacteria (4506 and 3508 μS cm-1). Aphanocapsa delicatissima showed markedly low conductivity optima in the lakes (2002 μS cm-1) respect to the obtained in the Salado River (8989 μS cm-1). It must be emphasized that ranges observed in lotic environments were wider than those in lentic environments. The species optima may be useful for future interpretations of the phytoplankton ecology and also as biological indicator for waterquality assessment in the studied environments.Instituto de Limnología "Raúl A. Ringuelet

Estudio preliminar de las relaciones tróficas en el plancton de una laguna arreica de la provincia de Buenos Aires: experimentación «in situ»

Shallow lakes can present two alternative stable states with or without submerged macrophytes that produce significant structural changes in plankton and nutrient dynamics. The aim of this study is to analyse the changes in the phytoplankton structure related to different conditions of zooplankton predation in an arreic lake. Four cylindrical pvc enclosures of 700 L of capacity were placed in the lake, two of them in free-vegetation waters and the other two in an area dominated by emerged and submerged macrophytes (Scirpus californicus and Potamogeton striatus respectively) with and without predation conditions on the grazer zooplankton. Samples were taken every eight hours for three days during the 2003/2004 summer period. Temperature, pH, dissolved oxygen, conductivity, turbidity and transparency were measured in situ. Water samples were taken to determine the different phosphorus and nitrogen forms and to analyse the phytoplankton. In all treatments, the conductivity oscillated between 1.520 and 1.550 μS.cm -1. Turbidity varied from 48 to 54 NTU and the pH was slightly alkaline (8,48-8,81). Chlorophytes and cyanophytes increased in free-vegetation-water enclosures with fish while no changes were found in the vegetated area. Preliminarily, we can say that the predation effect on zooplankton was more important in the enclosure placed in free-vegetation waters with fish. It was there that the biggest densities of eatable cholorophyte algae (Crucigenia quadrata, Dictyosphaerium pulchellum var. minor, Chlamydomonas sp. and Oocystis parva) were found towards the end of the experiment.Shallow lakes can present two alternative stable states with or without submerged macrophytes that produce significant structural changes in plankton and nutrient dynamics. The aim of this study is to analyse the changes in the phytoplankton structure related to different conditions of zooplankton predation in an arreic lake. Four cylindrical pvc enclosures of 700 L of capacity were placed in the lake, two of them in free-vegetation waters and the other two in an area dominated by emerged and submerged macrophytes (Scirpus californicus and Potamogeton striatus respectively) with and without predation conditions on the grazer zooplankton. Samples were taken every eight hours for three days during the 2003/2004 summer period. Temperature, pH, dissolved oxygen, conductivity, turbidity and transparency were measured in situ. Water samples were taken to determine the different phosphorus and nitrogen forms and to analyse the phytoplankton. In all treatments, the conductivity oscillated between 1.520 and 1.550 μS.cm -1. Turbidity varied from 48 to 54 NTU and the pH was slightly alkaline (8,48-8,81). Chlorophytes and cyanophytes increased in free-vegetation-water enclosures with fish while no changes were found in the vegetated area. Preliminarily, we can say that the predation effect on zooplankton was more important in the enclosure placed in free-vegetation waters with fish. It was there that the biggest densities of eatable cholorophyte algae (Crucigenia quadrata, Dictyosphaerium pulchellum var. minor, Chlamydomonas sp. and Oocystis parva) were found towards the end of the experiment

Influence of temperature and conductivity on the life-history characteristics of a pampean strain of Brachionus plicatilis

In the present work, we provide the first approach about the life-history of Brachionus plicatilis in South America. We tested with laboratory experiments the response of the pampean strain of B. plicatilis for two of its main stressors (conductivity and temperature). We evaluated the effects of eight conductivity values from 1 to 17 mS.cm-1 and two temperatures (15 and 25 °C) to compare its abundance with those obtained in the pampean lotic and lentic environments, where this rotifer is frequent or dominant. The results demonstrated that the increase in population-growth rate and the peak of abundance occurred at the highest temperature and at medium conductivity. Minimum values were obtained at the lowest temperature and conductivities analyzed, but the final density attained was nevertheless similar to those recorded in the pampean environments at the optimum conductivity and during the spring and summer seasons. Males, mictic females, and resting eggs were observed at the minimum and maximum conductivities, revealing the strategy of this species for maintaining dominance in environments with fluctuating salinity. The experiments also indicated the possible behavior of this relevant member of the zooplankton community within a scenario of increasing temperature and salinity related to the climate changes occurring in the pampean region.Instituto de Limnología "Raúl A. Ringuelet

Influence of temperature and conductivity on the life-history characteristics of a pampean strain of Brachionus plicatilis

In the present work, we provide the first approach about the life-history of Brachionus plicatilis in South America. We tested with laboratory experiments the response of the pampean strain of B. plicatilis for two of its main stressors (conductivity and temperature). We evaluated the effects of eight conductivity values from 1 to 17 mS.cm-1 and two temperatures (15 and 25 °C) to compare its abundance with those obtained in the pampean lotic and lentic environments, where this rotifer is frequent or dominant. The results demonstrated that the increase in population-growth rate and the peak of abundance occurred at the highest temperature and at medium conductivity. Minimum values were obtained at the lowest temperature and conductivities analyzed, but the final density attained was nevertheless similar to those recorded in the pampean environments at the optimum conductivity and during the spring and summer seasons. Males, mictic females, and resting eggs were observed at the minimum and maximum conductivities, revealing the strategy of this species for maintaining dominance in environments with fluctuating salinity. The experiments also indicated the possible behavior of this relevant member of the zooplankton community within a scenario of increasing temperature and salinity related to the climate changes occurring in the pampean region.Instituto de Limnología "Raúl A. Ringuelet

Seasonal Changes in the Vertical Distribution of Rotifers in a Eutrophic Shallow Lake with Contrasting States of Clear and Turbid Water

Monthly zooplankton samples were taken from a shallow Argentinean lake in 1997- 1998, and spatiotemporal changes in rotifers in the water column were examined. The most abundant and frequent species were Brachionus calyciflorus, B. caudatus, B. havanaensis, Keratella tropica, Filinia longiseta, and Polyarthra vulgaris. These perennial species are considered to be common in eutrophic waters, are eurytopic, and are widely distributed. The phytoplankton composition, competition for food with other grazers, and predation pressure, plus the occurrence of different periods including a turbid phase, a phase with coverage of submerged macrophytes (Potamogeton pectinatus), and a flooding phase, defined the annual planktonic rotifer succession in the lake. Small-scale vertical distributions of rotifers in this homothermal lake were related to both biotic and abiotic forces. The presence of macrophytes favored an increase in planktonic-rotifer densities along with a specific richness associated with the possibility of refuge, the incorporation of littoral species, and food diversification.Instituto de Limnología "Dr. Raúl A. Ringuelet