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Aquatic systems have traditionally played a key role in the development of human life, providing multiple ecosystem services to society and being a reservoir for a wide biodiversity of organisms. Among them, bacteria belonging to Legionella stand out, mainly because they are of great interest both in the field of microbial ecology and public health, since some of them turn out to be pathogenic for humans. The aim of this work was to study the monthly temporal dynamics of Legionella spp. and its relationship with the environmental variables measured in two Pampean shallow lakes (Gómez and Carpincho, Buenos Aires Province, Argentina). The analysis was carried out using a quantitative approach by real-time polymerase chain reaction (qPCR) and a non-quantitative approach using bacterial diversity data obtained by next-generation sequencing (NGS), using the Illumina MiSeq platform. Our results showed that the overall Legionella abundance was very high in the studied Pampean shallow lakes. Notably, fluctuations in dissolved organic carbon and temperature influenced the dynamics shifts in Legionella abundances. Correlation analyses between Legionella reads from NGS and copy numbers obtained through qPCR revealed positive relationships, unveiling distinctions attributable to the diverse sequence processing algorithms employed in the analysis of NGS data., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

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., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Bacterioplankton and bacterioperiphyton composition was analyzed using the CARD-FISH technique in three shallow lakes of the Pampean Plain (Argentina) with contrasting regimes: clear vegetated, turbid due to phytoplankton and turbid inorganic, due to inorganic particles. We postulated that these differences would influence the proportion of the main bacterial groups both in periphyton and in plankton. The turbid lake due to phytoplankton presented the highest total abundances in both communities. Alphaproteobacteria was the dominant group in the three lakes in both communities. Redundancy analysis (RDA) evidenced that the bacterioplankton structure was different among lakes and mainly influenced by dissolved inorganic nitrogen and conductivity. On the other hand, for the bacterioperiphyton, RDA showed that bacterial group abundances increased with higher periphytic chlorophyll-a values. In the clear lake the relative abundance of Betaproteobacteria and Cytophaga increased in the bacterioperiphyton towards the end of the colonization. Our study suggests that the lake regime (clear or turbid) influence the structure of bacterioplankton and bacterioperiphyton. [ABSTRACT FROM AUTHOR]

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]

[Display omitted] • We studied the drivers of planktonic chlorophyll a (Chl a) with a regional approach. • Shallow pampean lakes did not exhibited a positive TP-Chl a relationship. • Chl a was driven by submerged macrophytes, total nitrogen and agriculture. • Total phosphorus was the main driver of Chl a in lakes with submerged macrophytes. • For lakes without submerged macrophytes, Chl a was positively driven by the nearby agriculture of each lake. Although agricultural intensification has been linked with the increment of lake eutrophication and shallow lake research has demonstrated the importance of submerged macrophytes for maintaining water clarity, less is known about the role of macrophytes and the effects of agriculture on shallow lakes of the global south. Shallow lakes in the Pampean region of Argentina are subjected to high anthropic pressure and are classified as eutrophic and hypereutrophic and, in spite of most of them are turbid and dominated by phytoplankton biomass, some remain in a clear-vegetated regime with profuse submerged macrophytes. We studied the potential drivers of phytoplankton biomass (estimated as Chlorophyll- a - Chl a) by applying a regional approach and a model selection process for a dataset of 58 shallow lakes that represent the variability of the Pampean region. For the 58 lakes, the presence of submerged macrophytes, total nitrogen, and nearby agriculture of each lake were the main drivers of Chl a with −1.55, 0.19 and 0.02 coefficient values, respectively. Moreover, a high proportion of the variance in this dataset (37.7 %) was explained by the regional location of each lake (hydrographic systems). For lakes with macrophytes (N = 8), Chl a exhibited a positive relationship with total phosphorus (coefficient value = 3.05), whereas for lakes without macrophytes (N = 50) Chl a showed a positive relationship with nearby agricultural development (coefficient value = 0.02) and 36.4 % of variance explained by the hydrographic system. Our regional approach highlighted the importance of submerged macrophytes in shaping phytoplankton biomass in Pampean shallow lakes. Our results support the idea that the conservation of submerged macrophytes, as well as the control of agriculture in the riparian zones of lakes, will help to stabilize the shallow lakes in clear regime, even in regions highly impacted by agriculture and in lakes under eutrophic conditions. [ABSTRACT FROM AUTHOR]