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Palaeoenvironmental and palaeoclimatic inferences based on X-ray computer tomography: a case study of alkaline lake deposits in Hungary

Alzoubi Nour N., Gulyas Sandor, Geiger Janos

Geologos

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2023

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Vol. 29, No. 1

33--49

EN

Widely distributed freshwater carbonate sediments, i.e., limestone, dolomitic limestone and dolomite, developed in inter-dune alkaline ponds of the Danube-Tisza Interfluve in the centre of the Carpathian Basin during the Holocene. The key parameters that determine the formation of any given type of carbonate mineral (calcite, dolomite) are temperature, evaporation rate, pH and ion concentrations, in addition to CO2 absorption by aquatic plants. CT analysis is capable of recording small-scale density variations attributable to compositional differences of sedimentary rocks. As the type and proportion of rock-forming minerals and other components is an artifact of past environmental and climatic conditions, CT values may act as potential palaeoenvironmental proxies. The present study compares variations in rock-forming components obtained for freshwater carbonates utilizing the CT method with already available geochemical and palaeoecological proxy data. Variations in molluscan ecology and isotope geochemistry, sedimentation times and CT-based rock density values all indicate the relevance of millennial-scale, climate-driven changes in carbonate formation. As previously observed, the emergence of colder conditions in the North Atlantic, which resulted in increased cyclonic activity and heavier rainfall in western Europe and the Danube watershed area between 10.3 and 9.3 kyr cal BP, resulted in the emergence of humid conditions favouring a rise in the groundwater table at our site and precipitation of calcite from pore waters as opposed to high-magnesium calcite. This is clearly reflected in a negative shift in CT density values in our dated rock samples.

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Bioinvasions in fresh waters and the Nero dilemma

Gherardi Francesca

Polish Journal of Ecology

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2006

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Vol. 54, nr 4

549-561

EN

Human-mediated invasions of organisms are causing great harm to the environment, indigenous species, national economies, and human health. Notwithstanding Elton's (1958) prophecies, only by the mid 1980s did the negative impact of several introduced species become clear, along with the urgency to reduce the pace of bioinvasions. Often conservation biologists are faced with the Nero dilemma. Should they keep "fiddling" with their elegant experiments while biota are burning, or rather act, even before achieving a "strong verification" of their hypotheses? Indeed, we do need a comprehensive scientific understanding of the biological features, ecological effects, and spread potential of invasive species in order to be able to improve our strategies for mitigating their impacts. Abundant data have been collected during the past two decades on a growing number of case studies. The theories on bioinvasions derived from that wealth of knowledge have indeed revealed their predictive power. We should now strive towards a quick transfer of this knowledge from the laboratories to the real world.

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Biodiversity of freshwater microorganisms - achievements, problems, and perspectives

Weisse Thomas

Polish Journal of Ecology

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2006

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Vol. 54, nr 4

633-652

EN

The extent and significance of the diversity of freshwater microbes is at present controversially debated. Until 1980 it was assumed that there are no freshwater-specific bacteria and that the total number of bacterial species is low. The advent of molecular tools over the last ten years revealed that there is a bacterial freshwater assemblage which is phylogenetically different from soil and marine bacteria; secondly, it became obvious that the total number of cultured bacterial species ([similar to] 5900) underestimates bacterial diversity by several orders of magnitude. The current debate centres on 1) how to define a bacterial species and 2) if there is a microbial biogeography. The latter relates to the issue of ubiquity and cosmopolitanism, which is controversially discussed primarily in relation to eukaryotic microorganisms, namely ciliates. Although solid evidence is scarce, many microbial ecologists assume, in accordance with Baas Becking's famous 70-year old dictum - "everything is everywhere, the environment selects" - that freshwater microorganisms are easily dispersed and, therefore, potentially cosmopolitan. This review focuses on the often neglected second part of Baas Becking's metaphor. Evidence is accumulating rapidly that the environment does not simply act as a filter sensu Gleason's individualistic concept for widely dispersed microbes. Rather, prokaryotic and eukaryotic microorganisms have adapted to their specific habitat and perform better in this environment than newly invading congeners. There is an enormous ecophysiological diversity among closely related freshwater microbes which is neither obvious at the morphospecies level nor at the level of evolutionarily conserved genes, such as the small ribosomal RNA gene. Although this large diversity has been demonstrated for various groups of bacteria and protists, there is currently no measure available to compare microbial biodiversity across prokaryotic and eukaryotic domains. The current challenge is to link genetic divergence to ecophysiological diversity in the major taxa.