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Navegando por Autor "Huszar, Vera L. M."

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    Driving factors of the phytoplankton functional groups in a deep Mediterranean reservoir
    (Elsevier, 2010-03-20) Becker, Vanessa; Caputo, Luciano; Ordóñez, Jaime; Marcé, Rafael; Armengol, Joan; Crossetti, Luciane O.; Huszar, Vera L. M.
    The control of phytoplankton growth is mainly related to the availability of light and nutrients. Both may select phytoplankton species, but only if they occur in limiting amounts. During the last decade, the functional groups approach, based on the physiological, morphological and ecological attributes of the species, has proved to be a more efficient way to analyze seasonal changes in phytoplankton biomass. We analysed the dynamics of the phytoplankton functional groups sensu Reynolds, recognising the driving forces (light, mixing regime, and nutrients) in the Sau Reservoir, based on a oneeyear cycle (monthly surface-water sampling). The Sau Reservoir is a Mediterranean water-supply reservoir with a canyon-shaped basin and a clear and mixed epilimnion layer. The long stratification period and high light availability led to high phytoplankton biomass (110.8 fresh-weight mg L 1) in the epilimnion during summer. The reservoir showed P-limitation for phytoplankton growth in this period. All functional groups included one or more species (X2-Rhodomonas spp.; Y-Cryptomonas spp.; F-Oocystis lacustris; K-Aphanocapsa spp.) selected by resources, especially phosphorus. Species of Cryptomonas (group Y) dominated during the mixing period (winter season) in conditions of low light and relatively high availability of dissolved nutrients. Increases in water-column stability during spring stratification led to phytoplankton biomass increases due to the dominance of small flagellate functional groups (X2 and X3, chrysophyceans). The colonial chlorophycean O. lacustris (group F) peaked during the mid-summer stratification, when the mixed epilimnion was clearly depleted in nutrients, especially SRP. High temperature and increases in nutrient concentration during the end-summer and mid-autumn resulted in a decrease of green algae (group F) and increase of Aphanocapsa spp. (cyanobacteria, group K) and dinoflagellates (group Lo). The study also revealed the important role of physical processes in the seasonal gradient, in selecting phytoplankton functional groups, and consequently in the assessment of ecological status. The Q index (assemblage index) based on functional groups indicated the overall good ecological status of the Sau Reservoir, which varied as a function of the mixing regime. This is the first application of the Assemblage Index to a European water-supply reservoir
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    High Primary Production Contrasts with Intense Carbon Emission in a Eutrophic Tropical Reservoir
    (Frontiers Media, 2016-05-18) Becker, Vanessa; Almeida, Rafael M.; Nóbrega, Gabriel N.; Junger, Pedro C.; Figueiredo, Aline V.; Andrade, Anízio S.; Moura, Caroline G. B. de; Tonetta, Denise; Oliveira Jr, Ernandes S.; Araújo, Fabiana; Rust, Felipe; Piñeiro-Guerra, Juan M.; Mendonça Jr, Jurandir R.; Medeiros, Leonardo R.; Pinheiro, Lorena; Miranda, Marcela; Costa, Mariana R. A.; Melo, Michaela L.; Nobre, Regina L. G.; Benevides, Thiago; Roland, Fábio; Klein, Jeroen de; Barros, Nathan O.; Mendonça, Raquel; Huszar, Vera L. M.; Kosten, Sarian
    Recent studies from temperate lakes indicate that eutrophic systems tend to emit less carbon dioxide (CO2) and bury more organic carbon (OC) than oligotrophic ones, rendering them CO2 sinks in some cases. However, the scarcity of data from tropical systems is critical for a complete understanding of the interplay between eutrophication and aquatic carbon (C) fluxes in warm waters. We test the hypothesis that a warm eutrophic system is a source of both CO2 and CH4 to the atmosphere, and that atmospheric emissions are larger than the burial of OC in sediments. This hypothesis was based on the following assumptions: (i) OC mineralization rates are high in warm water systems, so that water column CO2 production overrides the high C uptake by primary producers, and (ii) increasing trophic status creates favorable conditions for CH4 production. We measured water-air and sediment-water CO2 fluxes, CH4 diffusion, ebullition and oxidation, net ecosystem production (NEP) and sediment OC burial during the dry season in a eutrophic reservoir in the semiarid northeastern Brazil. The reservoir was stratified during daytime and mixed during nighttime. In spite of the high rates of primary production (4858 ± 934 mg C m−2 d−1), net heterotrophy was prevalent due to high ecosystem respiration (5209 ± 992 mg C m−2 d−1). Consequently, the reservoir was a source of atmospheric CO (518 2 ± 182 mg C m−2 1 d− ). In addition, the reservoir was a source of ebullitive (17 ± 10 mg C m−2 d−1) and diffusive CH4 (11 ± 6 mg C m−2 d−1). OC sedimentation was high (1162 mg C m−2 d−1), but our results suggest that the majority of it is mineralized to CO2 (722 ± 182 mg C m−2 d−1) rather than buried as OC (440 mg C m−2 d−1). Although temporally resolved data would render our findings more conclusive, our results suggest that despite being a primary production and OC burial hotspot, the tropical eutrophic system studied here was a stronger CO2 and CH4 source than a C sink, mainly because of high rates of OC mineralization in the water column and sediments
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    Phytoplankton and its biotic interactions: Colin Reynolds’ legacy to phytoplankton ecologists
    (Springer, 2019-01-24) Becker, Vanessa; Sarmento, Hugo; Izaguirre, Irina; Padisák, Judit; Naselli-Flores, Luigi; Huszar, Vera L. M.
    The 18th workshop of the International Associationfor Phytoplankton Taxonomy and Ecology (IAP), thefirst ‘‘tropical’’ IAP ever, the third one outside Europe,and the first one in South America, was held in Natal,Brazil, from August 27 to September 3, 2017, and itsmain ecological theme was thePhytoplankton and itsbiotic interactions.The taxonomic topic of the work-shop was chosen based on function instead ofphylogeny, and to link to the ecological theme of theworkshop, the taxonomic theme was therefore cen-tered on mixotrophic microalgae
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    The success of the cyanobacterium Cylindrospermopsis raciborskii in freshwaters is enhanced by the combined effects of light intensity and temperature
    (PAGEpress, 2016-06-22) Becker, Vanessa; Bonilla, Sylvia; González-Piana, Mauricio; Soares, Maria C. S.; Huszar, Vera L. M.; Somma, Andrea; Marinho, Marcelo M.; Kokocinski, Mikołaj; Dukolil, Martin; Antonaides, Dermot; Aubriot, Luis
    Toxic cyanobacterial blooms in freshwaters are thought to be a consequence of the combined effects of anthropogenic eutrophication and climate change. It is expected that climate change will affect water mixing regimes that alter the water transparency and ultimately the light environment for phytoplankton. Blooms of the potentially toxic cyanobacterium Cylindrospermopsis raciborskii are expanding from tropical towards temperate regions. Several hypotheses have been proposed to explain this expansion, including an increase in water temperature due to climate change and the high phenotypic plasticity of the species that allows it to exploit different light environments. We performed an analysis based on eight lakes in tropical, subtropical and temperate regions to examine the distribution and abundance of C. raciborskii in relation to water temperature and transparency. We then conducted a series of short-term factorial experiments that combined three temperatures and two light intensity levels using C. raciborskii cultures alone and in interaction with another cyanobacterium to identify its growth capacity. Our results from the field, in contrast to predictions, showed no differences in dominance (>40% to the total biovolume) of C. raciborskii between climate regions. C. raciborskii was able to dominate the phytoplankton in a wide range of light environments (euphotic zone=1.5 to 5 m, euphotic zone/mixing zone ratio <0.5 to >1.5). Moreover, C. raciborskii was capable of dominating the phytoplankton at low temperatures (<15°C). Our experimental results showed that C. raciborskii growing in interaction was enhanced by the increase of the temperature and light intensity. C. raciborskii growth in high light intensities and at a wide range of temperatures, suggests that any advantage that this species may derive from climate change that favors its dominance in the phytoplankton is likely due to changes in the light environment rather than changes in temperature. Predictive models that consider only temperature as a drive factor can therefore fail in predicting the expansion of this potentially toxic cyanobacterium
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