Search

Abstract: The phytoplankton structure along the mainstem of the Lower Salado River (Argentina) was analysed in relation to the environmental variables and the influence exerted by the inflowing waters from the Paraná River (via El Vado Stream) and an adjacent floodplain shallow lake, between December 2003 and August 2004. Phytoplankton driving forces were explored using a functional approach. Small phytoplanktonic organisms with high metabolism and well adapted to live in mixed environments dominated (functional groups C, D, X1, X2), but the organic enrichment and slow flow also facilitated the thriving of Cyanobacteria (L O and minor contributions of H1, K, S N ) and large Euglenophyta (W1, W2) inflowing from adjacent sites. The longitudinal and temporal changes in the phytoplankton structure depended on the prevailing hydrological conditions. Three scenarios were identified as regards the complex hydrological interactions of the Paraná and Salado Rivers: (i) the hydrological isolation period (low waters) when the Salado had a homogeneous longitudinal pattern and high phytoplankton development; (ii) the period of hydrological interactions with Salado River influence (high waters) when the homogeneous longitudinal pattern extended to the stream, and algal growth in the river was counteracted by dilution and enhancement of water velocity, and (iii) the period of hydrological interactions with Paraná System influence characterised by a longitudinal discontinuity with lower phytoplankton concentrations downriver the Paraná inflow due to dilution. There were no evidences that the lake contributed with algal biomass to the downriver plankton during the study period. [Copyright &y& Elsevier]

Abstract: We examined the zooplankton abundance and composition of Laguna Grande, a floodplain wetland of the Lower Paraná Basin (Argentina), during an extraordinary drought–flood cycle that affected both the environment and the biological conditions of the lake. Low waters were characterised by remarkably high conductivities and pH values, and high phytoplankton and bacterioplankton abundances with cyanobacterial blooms, while high waters showed opposite features. In relation to zooplankton, the mean abundances of all the taxonomic groups (rotifers, cladocerans, copepods, ciliates, and heterotrophic nanoflagellates) were slightly higher at low waters. Major changes were observed in the specific composition of metazooplankton: the euryhaline species assemblage that dominated in the dry warm period was replaced by several oligohaline littoral and planktonic species characteristic of the Paraná River Basin, when the water level rose. Mean species richness values at high waters doubled those of low waters and were directly correlated to water depth. Most of the rotifers of the genus Brachionus and the cladoceran Moina micrura switched from parthenogenetic to sexual reproduction during low waters, as a response to a harsh environment and crowding. We suggest that the main changes in the environmental conditions in this eutrophic floodplain lake are driven by the hydrology, which regulates the zooplankton succession. The herein described shifts in the zooplankton structure and dynamics of Laguna Grande over an extraordinary drought–flood cycle contribute to the understanding of the processes that might occur under the scenarios predicted by climate change models. [Copyright &y& Elsevier]

Discusses an integrated study of water chemistry, phytoplankton and algal bioassays. Indication of distinct regions of a large river ecosystem; Characterization of three distinct reaches of the Lower River Lujan; Revelation of a progressive decrease of organic pollution parameters; Regulation of the limnology of the Lower Lujan River.

The ecological status of Pampean shallow lakes is evidenced by Cyanobacteria Harmful Blooms impairing these nutrient enriched, turbid and polymictic water bodies spread along the Central Plains of Argentina. Under the premise that shallow lakes are sentinels of global climate and eutrophication, a 3-year research in ten lakes located across a climatic gradient explored which factors drove the dynamics of cyanobacterial assemblages frequently driving to bloom prevalence. Contrarily to what is expected, the effect of seasonal temperature on cyanobacteria was subordinated to both the light environment of the water column, which was on turn highly affected by water level conditions, and to nutrient concentrations. Monthly samplings evidenced that cyanobacterial assemblages presented a broad-scale temporal dynamics mostly reflecting inter-annual growth patterns driven by water level fluctuations. Both species composition and biovolume gradually changed across a gradient of resources and conditions and hence, the scenario in each individual lake was unique with patterns at different temporal and spatial scales. More than 35 filamentous and colonial morphospecies constituted the assemblages of Pampean lakes: nostocaleans and chroococcaleans were inversely correlated in the prevailing interannual 3-cycled patterns. [Display omitted] • Bloom forming cyanobacteria prevail in shallow lakes immersed in impacted landscapes. • Interannual water level changes affect light conditions hence driving bloom dynamics. • Phosphorus and light interplay influence cyanobacterial assemblage structure. • Cyanobacterial blooms persist all year round in many pampean lakes. • Species temporal replacement evidences changes of morphological traits. Light conditions associated to water level fluctuations cause cyanobacterial bloom prevalence in eutrophic Pampean shallow lakes. [ABSTRACT FROM AUTHOR]

Vegetated wetlands are naturally subjected to changes in their water-level and macrophyte coverage leading to high habitat heterogeneity. The opportunistic ecological strategy of many planktic algae and bacteria makes them suitable for studying adaptive mechanisms to environmental change in wetlands at different temporal and spatial scales. In this study, we assessed the response of microbial aquatic organisms to sudden changes in habitat conditions, resulting from regime shifts involving the presence/absence of a dense floating-macrophyte cover, by means of a 72 h cross-transplant experiment using dialysis bags. Contrasting conditions imposed by the existing regime, such as light availability and dissolved oxygen concentration, accounted for the differences in phytoplankton and picoplankton compositions. Communities newly exposed to improved light and oxygen conditions exhibited a short-term (hours) response of C-strategists algae, such as small flagellated chrysophyceans. The onset of oxygen depletion and light impoverishment favoured the development of anaerobic anoxygenic photosynthetic bacteria (AnAnPB) and low-light adapted S-strategists (thin filamentous oscillatoriales) algae in few days. These results provide in-field evidence that phytoplankton and picoplankton assemblages are highly sensitive to environmental changes in a brief time scale, less than 72 h. Thus, these microbial organisms can act as sentinels to fluctuations in vegetated wetlands, also giving a quick response to sudden changes deriving from anthropogenic practices that impact on wetlands water-level and provoke fluctuations in their floating vegetation cover. [ABSTRACT FROM AUTHOR]