Publication details
Subfossil chironomid head capsules of filled up shallow lake Jurský Šůr near Bratislava, Slovakia - preliminary results
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| Year of publication | 2011 |
| Type | Conference abstract |
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| Description | This project is focused on vegetation and environmental changes in the Western Carpathians (Slovakia) during Late Glacial and Holocene period. The aim of this project is research of peats and lake sediment by using various analyses like palynology, macroremains, chironomids and geochemistry. The nature reserve Jurský Šůr is situated NE from Bratislava city (48o14'N,17o14'E). This former lake (2.8x4.3km) is situated in Danube lowlands (128-130 m a.s.l.) and bordering on NW the hillslope of the Small Carpathians.The site is covered by alder carr and particularly drained by artificial channels. The lake sediments, covering Pleistocene gravel-sands, are composed of organic material, fen and gyttja, which sediment in several periods of different sedimentation influx. The both, fluvial and lacustrine environments occur during the history of this shallow lake. Sediments were sampled to the depth of 245cm by the Russian peat sampler. The charcoals from bottom sand were dated around 25,000BP,and in the depth of 231cm is visible transition from the Glacial to the Holocene period.Pollen record shows dominance of pine and glacial refugia of broad-leaf trees (oak, elm, lime and hazel nuts) in the Glacial period.The Holocene record begins of beech expansion and pine decreasing. First anthropogenic indicators (corps) is appearing around 4,600BP.Holocene lake environment is changing to nutrient rich according to geochemistry evidence and macrofossil analyses, and lake has halofile features in this period.Analyses of green algae show boreal Pediastrum kawraysky in the Late Glacial and rich algae flora in the Holocene (P. boryanum agg.,P. duplex,P. integrum,P. angulosum, Scenedesmus sp. and Tetrahedron minimum).In the depth 162-132cm is visible regression of water level in green algae and according geochemical analyses.Last record of lake environment is in 93cm(approximately 3,200BP).Then the fine organic sediments sharply changing in anoxic fen nutrient-rich layer (96-0cm).The causes of lake filling up are not clear and uppermost layers are probably degraded by alder roots, which disable their analysis.The first three samples of subfossil chironomids up to 6 g (wet weight) from each layer was processed 20minutes under 70oC in 10%KOH, sieved on 100 microns mesh size and than the head capsules,their parts or remains of body has been separated under stereomicroscope (magnification up to 57x) and mounted in Naphrax.The remains of aquatic macroinvertebrates were identified for this pilot study only in three layers: uppermost lacustrine Holocene sediments (93-96cm), middle layer from the depth 216-219cm on Holocene begin and the lowermost Pleistocene layer (239-241cm). The Holocene sediment was mostly represented by Tanytarsini(i.e. Tanytarsus/Micropsectra agg.,Paratanytarsus penicillatus type),Chironomini(i.e. Endochironomus cf. albipennis type, Chironomus cf. plumosus type,Dicrotendipes nervosus type) and Orthocladiinae(Psectrocladius sordielus type). Chironomid residuals were accompanied by larvae head capsules of psychodids (Duckhousiella sp.),Ceratopogoninae and Ephemeroptera mandibles(Cloeon sp.).In the middle layer from the Holocene begin no remains of head capsules or body of any insect group or amphipod taxa were found. The lowermost Pleistocene sediment,very poor in subfossil residuals, was characterized by Chironomini (Glyptotendipes palens type,Microtendipes pedellus type,Microchironomus sp.) and Tanytarsini(Paratanytarsus sp.). The head capsules of Ceratopogoninae and remains of amphipods were also found in the Pleistocene layer.The occurrence of mentioned chironomid taxa in preliminary analyses indicate presence of warmer shallow lake covered in littoral zone by macrophytes(documented by miners), however higher number of treated layers is needed to for more reliable analysis of environmental changes during history of lake. |
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