Water quality changes in the Yugoslav part of the Danube river

Abstract

The paper describes specific changes in the quality of the Danube river water due to backwater effects in the Hydropower Plant Dj erdap 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 physico chemical and biochemical processes and in the biological status of the watercourse at varying reten tion 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 long term changes due to backwater effects in the reach of the Danube that was investigated. Settling of degradable organic matter promotes anaerobic processes in undistrubed 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 accu mulation of bottom sediments in the reservoir, the negative effects on water quality will be further intensified.

Indicators of unsustainable fishery in the Middle Danube

“…; Perisic et al. ; Brezeanu & Cioboiu ; Oguz & Gilbert ; Dokulil & Donabaum ). Future studies should be focused on resolving the influence of these factors on the observed trends in fish catch.…”

“…Without the expansion of fishing grounds, overall fishing pressure would have resulted in an even more pronounced decline of the mean catch-weighted trophic level (Kleisner & Pauly 2011). However, information regarding potential increases in the primary productivity in the Middle Danube over the studied period is not clear, as well as the complex influence of the construction of dams in the Iron Gates area and the consequent reduction of water flow in the upstream river section (Cociasu et al 1996;Perisic et al 1996;Brezeanu & Cioboiu 2006;Oguz & Gilbert 2007;Dokulil & Donabaum 2014). Future studies should be focused on resolving the influence of these factors on the observed trends in fish catch.…”