TERMINAL ELECTRON-TRANSPORT SYSTEM (ETS)-ACTIVITY IN THE SEDIMENT OF LAKE BALATON, HUNGARY

Terminal electron transport system (ETS)-activity of the sediment and plankton of Lake Balaton, the largest shallow lake of Central Europe was measured by tetrazolium-reduction biweekly during 1989-1990 and in the spring of 1991. Sediment proved to be enzymatically active to 30-35 cm down in the hypertrophic Keszthely Bay and to 15-20 cm down in the meso-eutrophic Siofok Basin. Sediment ETS-activity exceeded planktonic activity 15 to 24 fold. The total activity m-2 Showed one or two order of magnitude higher respiratory potential in Lake Balaton than needed for complete oxidation of the planktonic primary production; most of this potential was detected in the upper 3-5 cm sediment layer in springs. Incubations of cell-free homogenates of sediment bacteria showed that ETS remains active days after death of organisms at low temperature. Accumulated postmortem ETS-activity derived from the benthic diatoms, bacteria, plankton deposit and dead summer macrophytes seems to be responsible for the high ETS-activity of the sediment in the warming periods in springs. These enzyme fractions may contribute to the rapid oxidation of the alkaline, well-aerated lake.