1. Based on a comprehensive data set collected monthly during 8 years (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004), we evaluated the effects of mechanical removal of Eichhornia crassipes on the limnological characteristics and algal biomass of a polymictic shallow tropical reservoir. 2. Interrupted time series analyses indicated that the limnological responses to macrophyte removal can be classified as an 'abrupt permanent impact' implying that the overall mean of the time-series shifted promptly after intervention. These analyses indicated a significant increase for pH, total phosphorus, total phytoplankton and cyanobacterial biomass, and a decrease in water transparency and CO 2 concentrations in the surface water; also, the increase in water stability, increase of bottom soluble reactive phosphorus (SRP) and decrease in bottom oxygen levels. 3. Cyclic anoxic periods previously observed during springs and summers were replaced by a persistent period of anoxic conditions in the sediment overlying water. Anoxic conditions were suitable for SRP release from sediments. Heavy cyanobacterial blooms became more persistent, maximum biomass (4229 mm 3 L )1 ) was 30 times larger, the blooms frequently reached 2 m and sometimes the bottom of the reservoir, contrasting to the preremoval period in which it reached at most 1 m deep. 4. The long-term P dynamics in the system, initially driven by allochthonous nutrient loadings were replaced by internal ecological processes. Water hyacinth removal markedly accelerated the process of eutrophication due to internal feedback mechanisms, leading to a switch to a more turbid state. Biological feedback mechanisms were driven by cyanobacterial blooms by enhancing water stability, oxygen anoxia at the bottom and by increasing suitable conditions for P internal loading. These data support the hypothesis of the role of cyanobacterial blooms as an important factor impairing water quality and driving the ecosystem towards a stable degraded state. 5. These findings have important implications for the restoration of shallow stratifying eutrophic lakes, as the alternative degraded state is most likely to occur when compared with their non-stratifying counterparts. Moreover, feedback mechanisms in tropical and subtropical shallow lakes seem to be stronger than in temperate ones, as stratification events are more likely to occur over the year, intensifying system resilience to restorative strategies.

BackgroundThe regression of similarity against distance unites several ecological phenomena, and thus provides a highly useful approach for illustrating the spatial turnover across sites. Our aim was to test whether the rates of decay in community similarity differ between diatom growth forms suggested to show different dispersal ability. We hypothesized that the diatom group with lower dispersal ability (i.e. periphyton) would show higher distance decay rates than a group with higher dispersal ability (i.e. plankton).Methods/Principal findingsPeriphyton and phytoplankton samples were gathered at sites distributed over an area of approximately 800 km length in the Negro River, Amazon basin, Brazil, South America (3°08′00″S; 59°54′30″W). Distance decay relationships were then estimated using distance-based regressions, and the coefficients of these regressions were compared among the groups with different dispersal abilities to assess our predictions. We found evidence that different tributaries and reaches of the Negro River harbor different diatom communities. As expected, the rates of distance decay in community similarity were higher for periphyton than for phytoplankton indicating the lower dispersal ability of periphytic taxa.Conclusions/SignificanceOur study demonstrates that the comparison of distance decay relationships among taxa with similar ecological requirements, but with different growth form and thus dispersal ability provides a sound approach to evaluate the effects of dispersal ability on beta diversity patterns. Our results are also in line with the growing body of evidence indicating that microorganisms exhibit biogeographic patterns. Finally, we underscore that clumbing all microbial taxa into one group may be a flawed approach to test whether microbes exhibit biogeographic patterns.

-(Similarity among periphyton algal communities in a lentic-lotic gradient of the upper Paraná river floodplain, Brazil). Floristic comparison of periphyton communities from three systems with different hydrodynamic regimes (lentic, semilotic, and lotic) was carried out during high and low water periods on the Upper Paraná River floodplain. For each period and system, glass slides were sampled every two days during 18-day periods, and Eichhornia azurea Kunth petioles were sampled three times. A total of 228 species was collected, representing 12 classes, mainly diatoms and desmids. The highest species-richness was found in communities from lentic system and during high water. Species richness in the lotic system was more stable over succession and hydrological periods. Algal taxonomic structure in river community was clearly separated from the other two systems, with 43% of similarity level. The hydrological period was next in importance, followed last by the substratum type, with communities associated at 65-78% similarity levels, depending on system and hydrological period. The type of system, but not the water levels,was the main factor that influenced community richness, followed by disturbances caused by flood pulses and the operation of reservoirs upstream. The periphyton on artificial and natural substrata presented high degree of similarity.RESUMO -(Similaridade entre comunidades de algas perifíticas em um gradiente lêntico-lótico da planície de inundação do alto rio Paraná, Brasil). Comparação florística entre as comunidades perifíticas de três sistemas com distintos regimes hidrodinâmicos (lêntico, semilótico e lótico), abrangendo períodos de águas altas e baixas, foi realizada a partir de substratos artificial e natural. Lâminas de vidro foram coletadas a cada dois dias durante 18 dias e pecíolos de Eichhornia azurea Kunth três vezes em cada ocasião. O perifíton apresentou, como um todo, 228 espécies de algas distribuídas em 12 classes, com a maior representatividade de diatomáceas e desmídias. Maior riqueza foi, invariavelmente, encontrada no sistema lêntico e no período de águas altas. A ficoflórula perifítica foi caracterizada, principalmente, pelo regime hidrodinâmico e pela morfometria do ambiente, havendo nítida separação da comunidade do sistema lótico em relação à dos outros dois sistemas, agrupados a 43% de similaridade. Em seguida, o período hidrológico foi mais importante e, por último, o tipo de substrato, cujas comunidades se associaram a 65-78% de similaridade, dependendo do sistema e período hidrológico. Conclui-se que o tipo de ambiente e não o regime hidrológico exerceu a maior influência sobre a riqueza específica da comunidade; e que as perturbações causadas pelos pulsos de inundação e pela operação dos reservatórios influenciaram, marcadamente, as flutuações da riqueza específica das comunidades perifíticas. Finalmente, as comunidades epifíticas foram floristicamente bem representadas pelos substratos artificiais.

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