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Montevideo, Uruguay

Fabre A.,Seccion Limnologia | Carballo C.,Seccion Limnologia | Hernandez E.,University of Antioquia | Piriz P.,Seccion Limnologia | And 7 more authors.
Pan-American Journal of Aquatic Sciences | Year: 2010

Toxic cyanobacterial blooms are a global problem that is mainly exacerbated by cultural eutrophication. Although the factors driving the occurrence of blooms have been extensively studied in temperate systems, the evaluation of these processes at intermediate latitudes is limited. Given predicted increases in global average temperature, the study of subtropical lakes may also provide insights into the future dynamics of temperate lakes. Our aim was to explain the environmental factors influencing community structure and occurrence of cyanobacteria, including resources, mixing conditions, system morphology and zooplankton. We studied the phytoplankton and environmental characteristics of seven subtropical lakes in the southeast of Uruguay. We evaluated the relative importance of nitrogen and phosphorus on phytoplankton with cyanobacteria in laboratory microcosms. Our analyses indicated that the main environmental factors determining community structure were dissolved nitrogen and the euphotic/mixing zone ratio. Despite low temperatures (11-12 °C) some systems were dominated by cyanobacteria (Microcystis aeruginosa, Cylindrospermopsis raciborskii). Our experiments showed that larger species (>10 μm), including nitrogen fixing cyanobacteria, increased their growth rates with increasing nitrate concentration. In contrast, smaller species (<10 μm) responded to increased phosphate concentration. We observed that there was no correspondence between massive growth of cyanobacteria and lower diversity systems. Source

Rodriguez-Gallego L.,Seccion Limnologia | Meerhoff E.,Seccion Limnologia | Clemente J.M.,Seccion Limnologia | Conde D.,Seccion Limnologia
Hydrobiologia | Year: 2010

Hydrology is often the main determinant of water chemistry and structure of the aquatic communities in coastal lagoons, driven by the interaction of freshwater load from the catchment and marine intrusions. However, submerged aquatic vegetation (SAV) can have important local effects on both features, even during sporadically and short proliferations. A SAV summer proliferation was observed during 2003 in a coastal lagoon in Uruguay (Laguna de Rocha), increasing macrophyte cover and biomass in the less saline zones. SAV summer proliferations were first observed in summer 2001, with no records prior. The aim of this paper is to describe the ephemeral proliferation of SAV in this shallow brackish lagoon and to analyze its effects on the abiotic environment and on the zoobenthic community. Vegetated and unvegetated zones were sampled in the northern more limnic area (9.1 mS cm-1 ± 4.8) and the southern brackish area (20.9 mS cm-1 ± 5.2). Water and sediment chemistry were analyzed by standard methods and benthos and plants were collected with an Ekman grab. During SAV proliferation, suspended solids were five times lower inside macrophyte patches and water column total phosphorus and nitrogen were three and two times lower, respectively. Zoobenthos abundance and richness were higher in vegetated patches. However, no differences were found between sampling sites in the more brackish southern area and in the North after the SAV proliferation ended. This indicates that SAV can influence water chemistry and benthos structure above a biomass threshold of 100 g DW m-2. Although hydrology is the driving force regulating communities and water chemistry in these coastal lagoons, our results showed that SAV can also be an important local factor above a certain biomass threshold. © Springer Science+Business Media B.V. 2010. Source

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