Olga Urbanc-Bercic

Aquatic macrophytes of Lake Bled: changes in species composition, distribution and production

The macrophytes of Lake Bled were studied from 1987 to 1990. Three main factors influenced the decline of the aquatic vegetation in the lake during that period: (1) reduced light in the littoral zone due to an increase in phytoplankton (2) grazing by herbivorous fish and waterfowl, and (3) direct human impact.

Reed Stand Conditions at Selected Wetlands in Slovenia and Hungary

We determined the characteristics of reed stands at an intermittent lake in Slovenia and degraded and vital reed stands in Hungary. The disturbance in reed performance was measured through growth analysis, amino acid analysis in basal culm internodes, and photochemical efficiency of photosystem II (PSII) in leaves. Morphological parameters indicated higher disturbance in the development of degraded and intermittent reed stands in comparison to vital reed stands. Similarly, total free amino acid contents in basal culm internodes reflected temporary stress response in degraded and intermittent reed stands. On the other hand, potential photochemical efficiency showed undisturbed energy harvesting of all reed stands, even though actual photochemical efficiency revealed temporary disturbance of PSII. The most unfavourable condition for reed development seems to be degraded reed stand of Kis-Balaton wetland and littoral reed stand of intermittent Lake Cerknica.

Monitoring approach to evaluate water quality of intermittent lake Cerknica

The article presents the monitoring approach that is used to evaluate water quality of the intermittent Lake Cerknica and its tributaries. The results show that specific nature of Lake Cerknica influences the extent of the pollution. When regular gradual changes in water level occur the pollution effects can be buffered. The consequence of immediate decrease of water level is severe pollution of the main flow. The springs of the carstic tributaries are already loaded with pollutants which are transferred through underground pathways from neighbouring regions.

Water Quality and Macrophyte Community Changes in the Komarnik Accumulation Lake (Slovenia)

The Komarnik accumulation lake was built to retain high waters in the Pesnica valley. Nowadays it is used as an unfertilised fishpond. In order to estimate the human impacts we have monitored changes in macrophyte community for 5 years and changes in water chemistry during two vegetation periods. The values of chemical parameters indicated the input of nutrients and different ions entering the system through the run-off from the surrounding areas and by the tributary. At low water level during summer period, oxygen was lacking in the whole water column. The bottom and the water column of the lake were completely colonised by macrophytes comprising 17 species of different growth forms, among which Trapa natans and Ceratophyllum demersum prevailed. The Komarnik accumulation lake revealed to be a resilient system, since inter-annual changes of water level affected only species abundance and not species composition.