environmental pressures, impacts and stress

History of intervention and impacts on nature, in particular environmentally harmfull and damaging ones.

A review of official information on pollution sources within the Danube basin district between Iron Gate and the confluences of Osam and Olt rivers has been made. Economic activities located in this area are considered to have potential impact on the environmental quality of the Danube floodplain between Vidin-Calafat and Nikopol-Turnu Magurele. Nineteen industrial enterprises have been identified as significant sources of contamination based on data from the European Pollutant Release and Transfer Register (E-PRTR) referred to 2011.

Biological self-purification is carried out by aquatic organisms, not only plancton but also macrozoobenthos. When hydraulic engineering is done, one should try not to harm the aquatic organisms and to keep the sidearms connected, as they provide valuable habitat and serve as retention areas in flood events. In free flowing sections, natural bedload transport takes place and no macrophytes can settle down at the bed.

From may to august 1960, decomposition experiments with cotton- and silkthreads have been conducted in the Danube, the Inn and March by the S.I.L. .These experiments showed a noticeable low decomposition at sample station 2-3 (Danube-km 2411,2-2409,0 below Kelheim) and 11 (Danube-km 2093,6 Wallsee). While the decomposition hindering at Kelheim can be related to the discharge of industrial effluents in that region, this is not the case for Wallsee.

Recent years have witnessed a consistend spreading of the Pseudoraspora parva in the Danube region from East to West. Their existence was first discovered in UdSSR and the population has since spread upstream in the Danube and its tributaries. Even though this species is, at least in the Danube, exposed to great feeding pressure by predators, there is evidence of its rapid spreading.

This article deals with the Danube River and the different features and processes it inherits. This includes the riverbed, emerging land and rocks in the riverbed, different kinds of water within the river, ice on stream and lake, debris and bedload, the danube as way for navigation and structures in the water as well as weather and wind in regard to the Danube River.

Ditches, old river beds and small ponds comprise important biotopes for fish fauna, providing spawning grounds, as well as habitat and food sources for juvenile fish. These areas are very vulnerable to pressures such as river regulations or the construction of hydroelectric power plants. The article analyses human-induced changes in fish fauna based on the example of the Steyregger Graben, an oxbow lake [alluvial trench] of the Danube in Linz (Upper Austria).

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