Water quality changes in the Yugoslav part of the Danube river
Perisic, M. P.; Mihajlov, A. N.; Tutundzic, V. M.
The paper describes specific changes in the quality of the Danube river water due to backwater effects in the Hydropower Plant Djerdap I and II (Iron Gate I and II) storage reservoirs. The analysis includes changes in the content of suspended matter and turbidity, organic matter, oxygen regime and changes in the composition and abundance of plankton. This reservoir system differs from natural lake systems by a considerable oxygen deficit, especially pronounced during the period of autumn low-water flow, and by its low primary production. The study of specific changes in the physicochemical and biochemical processes and in the biological status of the watercourse at varying retention times completes the picture of short-term changes in the investigated system. The examination of settling effects and processes in the sediment of the reservoir provides an insight into some longterm changes due to backwater effects in the reach of the Danube that was investigated. Settling of degradable organic matter promotes anaerobic processes in undisturbed bottom sediments. Sediment erosion and transport under high water conditions lead to aerobic decomposition which also affects water quality (oxygen regime, contents of organics and undissolved matter). With a permanent accumulation of bottom sediments in the reservoir, the negative effects on water quality will be further intensified.