Unexpected stability of a shallow lake ecosystem (Lake Komořany, Czech Republic) despite rapid climate change at the Late Glacial/Holocene boundary
Abstrakt
Sediments of central European lowland lakes are valuable, but little studied natural archives. The image of postglacial landscape development was mostly formed by study of alpine lake records.
Our study investigated the response of a large shallow lake ecosystem (former Komorany Lake, 50.53°N, 13.53°E, surface area ~25 km2) to abrupt environmental changes at the Late Glacial/Holocene boundary. Sediment cores obtained in the 1980s by rescue sampling were subsampled and four bulk samples were selected for AMS radiocarbon dating.
Analyses of biological variables (diatoms, chironomids, pollen) were accompanied by XRF and LOI. The agedepth model provided evidence for a continuous Late Glacial to early Holocene record, supported by the palynostratigraphy.
The alkaliphilous tychoplanktonic diatom Staurosira dominated throughout the studied profile. They were, however, partly excluded from counting and analyses considering their low indicator value.
Although algal productivity rose distinctly with amelioration of climate conditions at the start of the Holocene, no remarkable change in diatom species composition was observed. The only significant changes in the diatom and chironomid assemblages occurred slightly before the onset of the Holocene: the tychoplanktonic diatom Staurosira venter that dominated the basal part of the profile was replaced by Staurosira construens.
The abundance of Chironomus plumosus-type and Chironomus anthracinus-type decreased and Procladius, Einfeldia dissidens/natchitocheae and Glyptotendipes pallens-type were established. Palynological data indicatedthe presence of aquatic macrophytes since the Late Glacial.
Our results suggest very consistent in-lake conditions, with high nutrient availability that enabled the aquatic community to maintain a stable structure at the Late Glacial/Holocene boundary. The trophic status even decreased slightly in the Holocene.
During the Late Glacial/Holocene transition the eutrophic lakes likely represented very stable ecosystems despite drastic changes in the surrounding landscape.