Navegando por Autor "Costa, Mariana R. A."
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Artigo Extreme drought favors potential mixotrophic organisms in tropical semi-arid reservoirs(Springer, 2018-03-16) Becker, Vanessa; Costa, Mariana R. A.; Menezes, Rosemberg F.; Sarmento, Hugo; Attayde, José L.; Sternberg, Leonel da S. L.Climate change is affecting the global hydrological cycle and is causing drastic changes in the freshwater hydrological regime. Water level (WL) reduction caused by drought tends to increase the concentration of nutrients favoring the dominance of cyanobacteria. We hypothesized that the WL reduction favors the dominance of cyanobacteria at regular dry conditions, but at extremely dry events mixotrophic algae would thrive because of light limitation due to increased resuspension of sediments on the water column. To test our hypothesis, we compared phytoplankton traits and water quality variables between two sets of reservoirs located in two watersheds with contrasting precipitation regimes within the Brazilian semi-arid. The reservoirs were compared in a dry period and in an extremely dry period to evaluate the response of the variables to an extreme drought. Drought intensification decreased the reservoirs’ WL and water transparency and increased the total phosphorous. Cyanobacteria dominated in the dry period, and the contribution of mixotrophic algae increased in the extremely dry period. Thus, phytoplankton with mixotrophic potential was favored by the extreme drought. This result suggests that this can be one possible scenario for phytoplankton communities in reservoirs of semi-arid regions if extreme droughts become more frequent because of climate changeArtigo 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, SarianRecent 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