Objective and research questions: The main focus in terms of the Danube CS3 at the whole basin scale will be on hydro-morphological pressures at catchment and regional scales, focusing on alterations in longitudinal and lateral connectivity, and on the consequences of these. CS3 also includes the Danube Delta, where the effects of eutrophication are studied at regional scale, focusing on the impact of hydro-morphological alteration (lakes and floodplains along the Danube Delta’s channels). Thereby, we explore trade-offs and synergies of biodiversity and ecosystem services related to hydro-morphological alterations of the River Danube and its tributary rivers.

The Danube River Basin (see map) is the most international river basin in the world shared by more than 80 million people from 19 countries, all contracting parties of the International Commission for the Protection of the Danube River (ICPDR), which coordinates the conservation, improvement and rational use of Danube waters. The Danube connects with 27 large and over 300 small tributaries on its way from the Black Forest to the Black Sea with a catchment size of approximately 800,000km². Accordingly, a huge variety of human activities and related pressures are affecting this area. 

Hydro-morphological alterations, such as river fragmentation or disconnection of wetlands, are seen as most relevant threats to riverine ecosystems and their biodiversity in general (e.g. Vörösmarty et al. 2010; Schindler et al. 2016) and are specifically relevant in the area of the Danube catchment (e.g. Hein et al., 2016, ICPDR, 2015). The alteration of natural hydro-morphological conditions can have negative effects on aquatic populations, which might result in failing the EU WFD environmental objectives of reaching a “good status” of all EU surface waters. The most relevant human activities identified in a risk analysis were hydropower, navigation, flood protection and agriculture (ICPDR, 2015).

In the Danube catchment there is a large number of hydrological alterations, such as water abstraction, impoundments and hydropeaking (ICPDR, 2013). The construction of hydropower dams represents one of the most severe pressures affecting the integrity of river ecosystems, as it involves the modification of riverine habitats, the transformation of a river section into reservoir stretches, modifications of the hydrological regime, of water temperature, turbidity, sediment load, and the interruption of river continuity, which may cause large-scale effects for the whole river system (Parasiewicz et al., 1998; Vörösmarty et al., 2003; Gracey & Verones, 2016). Thus, the construction of hydropower dams represents a clear threat to regional aquatic biodiversity and to several ecosystem services provided by river corridors to humans (Dugan et al., 2010; Wang et al., 2010)

Disconnection of floodplains and wetlands represents another significant hydro-morphological alteration in the Danube River Basin. This includes channelization and reduction of lateral exchange processes and floodplain areas (ICPDR, 2015a). The extent of floodplains in the Danube River Basin has been reduced by 68% (Hein et al. 2016). Nevertheless, river-floodplain systems still represent hotspots of biodiversity conservation and provide multiple ecosystem services (Hein et al. 2016, Schindler et al 2016). Protected areas play a key role in the maintenance of biodiversity in large river systems (Tockner and Stanford, 2002). Multiple human activities, including the expansion of agricultural use and large-scale river regulation measures designed to improve navigation and flood protection, have resulted in this ongoing loss of habitat and biodiversity (Hein et al. 2016, ICPDR, 2015).

Moreover, the effects of morphological changes and degradations in combination with hydrological alterations from the basin headwaters to the Danube Delta are not sufficiently understood (Habersack et al. 2016). The Danube Delta is located in the south-eastern part of Europe, having 84% of the total area in Romania and it is one of the largest protected areas in Europe (5.800 km²).

Approach: In AQUACROSS CS3, the effects of multiple human activities on aquatic biodiversity and ecosystem services are evaluated for the Danube River. Thereby the AQUACROSS linkage framework (developed in Work Package 4 and Work Package 5) is used to explore linkages between various human activities, pressures, ecosystem components, ecosystem functions and ecosystem services at basin scale. A policy analysis supports the identification of challenges in implementation of existing policies and the identification of appropriate EBM responses. A quantitative approach specifically focuses on the navigable main stem of the Danube River, where the interactions of several human activities and pressures related to hydro-morphological alteration on biodiversity and ecosystem services are quantified. Relationships are analysed using a quantitative Bayesian network approach (Korb & Nicholson, 2004).

Solutions: Potential measures aiming to support EBM include several alternatives of hydro-morphological restoration and remediation measures for river sections and their floodplains. Restoration of the main channel and re-connection of floodplains and wetlands aim to increase hydro-morphic dynamics and resilience as well as ensure biodiversity or flood protection. Morphological restoration of rivers as well as protection, conservation and restoration of wetlands/floodplains are defined as measures of basin-wide importance to conserve biodiversity (EC, 2011, Target 2), ensure the good status in the river stretch, flood protection, pollution reduction and climate adaptation by 2021 (ICPDR, 2015a). Due to the strong linkage between Danube Delta and Danube River policymakers should exploit at local and regional level actions that can increase the institutional cooperation that is needed to mitigate the effect of cyanobacteria blooms and its potential toxic effect on aquatic diversity. Those actions must be address to reducing eutrophication all over the Danube Basin.

Area: Danube River Basin (see map)

Lead partner organisation: The Institute of Hydrobiology and Aquatic Ecosystem Management (IHG) is one of seven institutes within the Department of Water, Atmosphere and Environment at the University of Natural Resources & Life Sciences, Vienna (BOKU) is leading the research in the case study with close collaboration with Danube Delta National Institute for Research & Development (DDNI).

Cooperating partner: The International Commission for the Protection of the Danube River (ICPDR) is an International Organisation consisting of 14 cooperating states and the European Union. Since its establishment in 1998, the ICPDR has grown into one of the largest and most active international bodies of river basin management expertise in Europe. The ICPDR deals not only with the Danube itself, but also with the whole Danube River Basin, which includes its tributaries and ground water resources. It works to ensure the sustainable and equitable use of waters and freshwater resources in the Danube River Basin. The work of the ICPDR is based on the Danube River Protection Convention, the major legal instrument for cooperation and trans-boundary water management in the Danube River Basin.

Edith Hödl is the case study representative and acts as Technical Expert for River Basin Management in the International Commission for the Protection of the Danube River (ICPDR) located in Vienna. She is responsible for the technical support of ICPDR Contracting Parties on issues related to river basin management as well as the coordination of the implementation of the EU Water Framework Directive including the review and updates of the River Basin Management Plan. Ms Hödl is advising technical experts and expert groups on relevant EU Directives and Regulations in the field of river basin management.

Area: 

Danube River Basin