engleski

Trophic state of Lake Sakadaš (Nature Reserve Kopački rit, Croatia) in the late autumnal and winter period of 1997/98

Background and purpose: Lake Sakadaš, the deepest lake in the complex wetland ecosystem of the Kopački rit Nature Reserve, was under the influence of untreated waste waters during the 1980s. The improvement of water quality and decrease in eutrophication were registered in the period from its revitalisation (controling of waste waters and sediment removal) till the beginning of the war activities (1991). The aim of this paper is to establish the trophic state of Lake Sakadaš according to the first post-war hydrobiological research done in the late autumnal and winter period of 1997/98. Material and methods: Sampling was done at monthly intervals from November 1997 till March 1998 (except in February) at one site in the central part of the lake. Physical and chemical characteristic of the surface and contact zone sediment-water were determined according to standard methods. Qualitative and quantitative analyses of phytoplankton and zooplankton, as well as chlorophyll-a analysis were done at three water depths. The Shannon-Weawer diversuty and ANOVA were used for the statistical analysis of results. Results: Oxygen depletion in November caused mass fish mortality for a short time but with significant consequences on the lake ecosystem. High concentration of ammonium and nitrate, as well as organic matter, and low Secchi transparency were recorded during the entire period. In the extremly abundant phytoplankton community Euglenophyceae were constantly well developed. Mass development of Synura observed was in December and January while in March the predominance was gained by centric diatoms. The absolute dominance of rotifers, namely microfilter-feeder populations, was the main characteristic of the zooplankton community. Conclusions:With respect to all data, high eutrophic to hypertrophic condition of Lake Sakadaš in the late autumnal and winter period of 1997/98 was proved. In comparison with investigation results obtained before the war, the increase in the level of eutrophication is evident.

wetland ecosystem; phytoplankton; zooplankton; trophic state

nije evidentirano