engleski

Mass mortality event in a small saline lake (Lake Rogoznica) caused by unusual holomictic conditions

The study of small saline eutrophic lake was performed under the meromictic and holomictic conditions. Meromictic period is characterised by anoxic conditions in the bottom layer with high sulphide and nutrients concentrations. The depth of the nutricline varied as affected by thermohaline conditions in the water column. In late summer 1997, holomictic conditions replaced ordinary meromitic conditions of the lake. This transformation caused anoxia to spread throughout the water column to which mass mortality of almost all the organisms' occured. Upon this event, oxic conditions were re-established slowly as the new phytoplankton population developed. As the consequence of the particulate organic matter decay inorganic N and P concentrations increased and were doubled approximately six weeks after the mass mortality. The revitalisation of the phytoplankton population was initiated immediately after the mass mortality by the development of "microflagellatae" species, which were favoured by the high ammonia concentrations. The larger phytoplankton species (diatoms and dinoflagellatae) were developed at the expense of smaller ones when nitrate became dominant nutrient in the water column. A year after the mass mortality the composition of the phytoplankton population was the same as before.

saline lake; mass mortality; holomictic; meromicic

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