Výsledky projektu Analýza environmentálně podmíněných změn krytenkových biocenóz v pozdním pleistocénu a holocénu

Microbioerosion structures are a common sign of microbial activity known mainly from marine environments and calcareous substrates, or from pollen records. However, the same phenomenon has been overlooked in animal fossils preserved in lake sediments. We studied 430 fragments of chitinous microfossils from three central European glacial lakes and detected microboring structures in approximately 10%. The microfossils belong to two size groups: (1) spherical objects with lengths ranging from 50 to 300 μm that are probably microturbelarian (Turbellaria: Rhabdocoela) cocoons, and (2) larger remnants (up to 2 mm long) of caddisfly (Insecta: Trichoptera) frontoclypeal apotomes. Four microbioerosion morphotypes were distinguished: (1) small holes (< 0.6 μm) oriented perpendicular to microfossil walls, likely produced by bacteria or fungi; (2) simple meandering tunnels and; (3) asterisk-like tunnel structures produced by fungi and/or fungus-like organisms; and (4) abrasions caused by biofilms. The maximum diameter of the simple holes and both tunnel structures depended on host-microfossil size: a higher diversity of microbioerosions was found on larger chitinous fragments. We propose that the good preservation of microfossils in the studied sediment samples might be due to rapid transport to the anoxic profundal zone or by rapid burial in anoxic sediments.

The Bohemian Forest lakes are situated along the Czech-German-Austrian border. In addition to the existing eight glacial lakes, other eight infilled lakes were found so far. These sites represent important natural archives, allowing reconstructions of past environmental changes since the end of the last deglaciation. Although these sediments became a subject of increasing scientific interest during the last decades, a comparison among the individual lakes is still lacking. To fulfil our research aim, we studied lake sediment cores from three localities (Plešné jezero, Prášilské jezero, Stará jímka) and compared them with the published data on other two sites (Malé Černé jezero, Rachelsee), using AMS radiocarbon dating simplified description of the lithology, and LOI. Sediments of Late Glacial age contain aseries of silt- and clay-dominated layers with low proportion of organic matter indicated by LOI with concentrations usually <10%. In contrast, the Holocene sediment consists of gyttja. In the infilled lakes, this sediment gradually becomes peaty in the upper layers. The oldest 14C date based on AMS dating of terrestrial plant remains corresponds to the Bølling interstadial. Despite repeated sampling, no evidence of Late Glacial sediments was documented in Prášilské jezero. Based on the first results obtained from the sediment cores, we conclude that:– The age of sedimentation onset in the Bohemian Forest lakes may differ from age of the moraines damming the lake water.– The oldest natural archives represented by the Bohemian Forest lake sediments cover at least the whole Late Glacial period. – Besides individualities in historical development of each catchment, the lake sediments reflect the general regional changes due to climatically driven deglaciation and forest establishment.– The future investigation of the Bohemian Forest lake sediments needs to be based on a uniform and coherent approach.