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Thermo-mineral springs are specific ecosystems with extreme environmental conditions that constitute interesting models for studying metacommunity processes. Since these springs can be considered as islands within a terrestrial context, we first aimed to test some predictions of the theory of island biogeography and the distance-decay hypothesis on benthic diatom communities. Then, we aimed to quantify the influence of physical, chemical, climatic and spatial factors on species assemblages. We evaluated the species-area relationship for all springs and for several group of springs classified according to their environmental and hydrochemical composition. The influence of environmental variables on α-diversity was tested. We also investigated whether β-diversity was related to spring isolation or changes in environmental conditions. Finally, we determined the importance of environmental and spatial variables in shaping diatom communities using ordination and variation partitioning. We did not find any species-area relationship whatever the group of springs investigated, and no geographical distance-decay pattern was observed. We found a significant effect of physical and chemical parameters on α-diversity and composition. Thus, diatoms communities of thermo-mineral springs did not seem to be influenced by dispersal processes at the scale of our study but appeared to be patterned by physical and chemical factors. [ABSTRACT FROM AUTHOR]

Although a strong link between viruses and prokaryotes is commonly known to exist in aquatic systems, few studies have investigated their relationship in spring waters. In the French Massif Central, certain springs are known to exhibit varying levels of naturally occurring radioactivity. Therefore, the aim of this study was to examine the standing stock of viruses together with prokaryotes and determine the potential environmental factors influencing them in springs characterized by contrasted radioactivity gradient. Among the investigated 15 spring habitats, flow cytometry analyses indicated that both viral (VA) and prokaryotic abundances (PA) varied by an order of magnitude accompanied by virus-to-prokaryote ratio ranging between 8 and 144.2. Significant differences in VA was evident among springs where low abundances (mean ± SD: 21.3 ± 7.0 × 107 VLP l−1) corresponded to high (mean ± SD: 1911 ± 814.0 nGy h−1) gamma (γ) dose radiation (222Rn) and vice versa. Adverse effect of water radioactivity (222Rn) on VA could perhaps corroborate our hypothesis of drastic effect of ionizing radiations on viruses, which might explain for lack of significant relationship between PA and VA. In such a scenario of prevailing low VA, the adopted phage life strategies could define their existence in these specialized ecosystems. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) controls the degradation and sequestration of aquatic pollutants and, in turn, water quality. In particular, pollutant degradation is performed by oxidant species that are generated by exposure of DOM to solar light, yet, since DOM is a very complex mixture of poorly known substances, the relationships between potential oxidant precursors in DOM and their oxydative capacity is poorly known. Here, we hypothesized that production of oxidant species could be predicted using fluorescence analysis. We analysed water samples from an alluvial plain by fluorescence spectroscopy; the three-dimensional spectra were then decomposed into seven individual components using a multi-way algorithm. Components include a protein-like fluorophore, e.g. tryptophan-like and tyrosine-like, three humic fluorophores, 2-naphthoxyacetic acid, and a by-product. We compared component levels with the ability of water samples to generate reactive species under solar light. The results show a strong correlation between reactive species production and the intensity of two humic-like fluorophores assigned to reduced quinones. Monitoring these fluorophores should thus allow to predict the ability of DOM degradation of pollutants in surface waters. [ABSTRACT FROM AUTHOR]