Hidrológiai Közlöny, 2017 (97. évfolyam)

2017 / 3. szám - TRANSNATIONAL EFFORTS - Sandu, Cristina - Dumitrache, Alina - Radu, Emilia - Dobre, Doru - Tudorache, Mädälina - Mihăilescu, Simona: The importance of good ecological status for the successful revival of Danube sturgeon

Cristina Sandu et al: The Importance of Good Ecological Status for the Successful Revival of the Danube Sturgeon

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consumption of contaminated food and water, pesticide residues in food or beverage, or leaching chemicals from food and beverage containers (Kabir et al. 2015).

Besides pharmaceuticals, plastic pollution is of growing concern, especially considering its impact on the marine environment, aquatic organisms and human health: besides entanglement and ingestion of macro debris by large vertebrates, microplastics are accumulated by planktonic and invertebrate organisms, being transferred along food webs. Negative consequences include the loss of feeding ability, physical damage, exposure to pathogens and transport of alien species. In addition, plastics contain chemical additives and efficiently adsorb other toxic environmental contaminants, thus representing a potential source of exposure to such compounds after ingestion (Avio et al. 2017).

Close cooperation on the implementation of WFD, Marine Strategy Framework and REACH directives are needed in order to develop a new strategy for a non-toxic aquatic environment in the DRB and the Black Sea, by e.g. (i) extending the monitoring programmes to more hazardous substances, (ii) studying the synergistic effect of chemical combinations on aquatic biota and human health, (iii) minimizing production, use and exposure to known harmful substances, (iv) producing new generation materials with lower health risks, (v) adopting stronger environmental regulations preventing pollution with such substances, etc.

HYDROMORPHOLOGICAL CHARACTERISTICS

In the past decades, it has been increasingly acknowledged that river channels, riparian areas, floodplains and aquifers form a unitary riverine system, where hydrological connectivity and the exchange of matter and energy among these components ensure the functioning of the ecosystem. This hydrological connectivity takes place in longitudinal, lateral and vertical dimensions and over time (Ward 1989), and its loss constitutes the main cause of the ecological degradation of rivers (Wohl 2004). Hy- drotechnical constructions, such as hydropower dams, embankments and dikes for flood protection, channelization by cutting meanders and side arms to meliorate navigation, gravel extraction and water abstraction for various human uses (irrigation, industrial or household use, etc.) and the subsequent alteration of flow dynamics and sediment transport, river bed incision, increased bank erosion, reduced capacity of floodplains to store water and buffer floods and droughts, severely affect the life of the aquatic communities and the functioning of the ecosystem (Sandu 2005). This impact is worsened by climatic changes, as increasing temperatures and modified precipitation regime may dramatically alter river discharge, sediment transport and dissolved oxygen content, with increasing occurrence of hypoxia and fish mortality (Sandu et al. 2009). Vertical connectivity is also affected by decreased flow dynamics, as fine sediments can accumulate on the river bed and reduce permeability (Kondolf and Wilcock 1996), affecting the incubation and survival rates of fish embryos dependent on the upwelling or downwelling of groundwater, like in the case of salmonids (Baxter and Hauer 2000).

For the River Danube, it is presumed that the construction of the Iron Gates dams has led to a reduction of sediment transport by 55% (Teodoru and Wehrli 2005), which affects river geomorphology, intensifying the erosion processes in the Danube Delta and along the NW Black Sea coast. Moreover, at river basin level, over 80% of the floodplains have been destroyed or lost their function. The situation, however, differs along the river, as in the Upper Danube, over 95% of the floodplains have been lost, while in the Middle and Lower Danube about 25-30% are still available (Schneider 2002).

Given the considerable impact of hydromorphological alterations on water quantity and quality, this is considered a Significant Water Management Issue (SWMI) by the International Commission for the Protection of the Danube River (ICPDR). Consequently, the Danube River Basin Management Plan recommends measures to restore river continuity interruptions along the River Danube and its main tributaries (ICPDR 2015), some of the most important ones targeting the restoration of fish migration at the Iron Gates dams, which could have a significant positive effect on the critically endangered sturgeon populations, reopening their access to major tributaries such as the rivers Tisza, Drava and Sava and to an additional 800 km of habitats located along the River Danube.

However, due to the inclusion of the River Danube in the TEN - T corridor for navigation (Rhein - Main - Danube), the Middle and Lower stretches of the River Danube are subject to additional technical measures that jeopardize the current conservation efforts undertaken by the Danube Sturgeon Task Force in the framework of the EU Strategy for the Danube Region Priority Areas 6 (Biodiversity) and 4 (Water quality). In particular, a submerged construction located at the bifurcation of the Old Danube and Borcea secondary arm (approx. Danube rkm 345), hinders sturgeons’ spawning migration upstream this sector, threatening with extinction the long distance migrants that should be eventually supported to pass the Iron Gates and migrate towards the upper reaches of the Danube. A second navigation melioration project will soon start on the Romanian - Bulgarian stretch of the Danube, between the Iron Gates II and Danube rkm 375, with the potential to create additional negative impacts on Natura 2000 protected species and habitats located along this river section. Flood protection measures, plans to erect additional hydropower dams or to develop new reactors at the existing nuclear power plants located along the River Danube, water abstraction for irrigation and tourism development complete the picture of future hydromorphological alterations foreseen along the River Danube. A strategic environmental assessment of their cumulative impact will allow a better understanding of the magnitude of future changes as well as of the risks to achieving WFD requirements.

An intensified dialogue between environmental stakeholders (governmental and non-governmental organizations, research institutes, local authorities, etc.) and infrastructure development companies is needed in order to identify environment-friendly solutions and avoid/mitigate the impact of future technical development