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Zooplankton of Bohemian Forest lakes as indicator of recovery from acidity
Kohout, Leoš ; Fott, Jan (advisor) ; Macháček, Jiří (referee) ; Bitušík, Peter (referee)
CONCLUSIONS In my Ph.D. thesisthe ťollowingitems arediscussed It is hypothesisedthat Al govems the P availability in the acidified lakes, as well as shapesthe foodweb structure. Substantialportion of the plankton biomass in the Bohemian Forest lakes is createdby hetelotrophic fi|amentswhen filtering cladocerans aÍenot present (theyareextinctor occuÍseasonal1y). After ťrrstsigns in the nineties further evidence for the ongoing biological recovery was collected. Nevertheless, the lakes are still stongly or partially influenced by acidification and standardfood web relationshipshave not been restored. The significant hysteresisof biological recovery behind the reversal of lake chemistryin theBohemianForest and elsewherecould have severalreasons: - Isolationofremote headwaterlakes makestheprocessofzooplankton re- colonizationstochastic,theprobability being atleastfor somecnrstacean specieslow. The successdependson suitablevector ofpropagules and size of inoculum. - Strong invertebrate predation in some fishless lakes can cause abiological resistancepreventing from zooplankton recovery until fish retum. ln theBohemian Forest for instancethereaÍeknown populations of corixids in some lakes and numerousChaoborus larvae are observed from Laka Lake. - Currenthydrochemicalconditions are still hard for...
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Palaeoenvironmental reconstruction of the Younger Dryas based on fossil chironomids
Skurčáková, Anežka ; Tátosová, Jolana (advisor) ; Bitušík, Peter (referee)
The final stadial of the last glacial - Younger Dryas (12 650 - 11 500 cal yr BP) is relatively well described in sediments of European lakes, however research related to its progress in Central European area is missing. The goal of this thesis was to examine progress of this stadial based on sediment core from Černé Lake at Šumava (Czech Republic). To reconstruct climatic conditions, sub-fossil remains of Chironomidae was used. The air July temperature was estimated using Swiss-Norwegian model. Geochemical analysis was performed to determine intensity of erosion, trophic status of the lake, and sources of its organic matter. To complete information about catchment, pollen analysis was performed. Following climatic events were identified in the sediment: Older Dryas (13 583 - 13 394 cal yr BP), Alleröd (13 394 - 12 383 cal yr BP), Younger Dryas (12 383 - 11 394 cal yr BP) a Early Holocene (11 394 - 11 138 cal yr BP). Presence of two phases of Younger Dryas was not significantly proven, nevertheless, the isotope composition suggests, that the first half of this oscillation was drier. Reconstructed temperature ranged between 8,30 and 10,31řC. The mean temperature for Older Dryas event was 8,92 řC, for Alleröd 9,61 řC, Younger Dryas 9,17 řC and Early Holocene 10,00 řC. Reconstructed temperature...
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