Current status and restoration options for floodplains along the Danube River
Graphical abstract
Introduction
Floodplains are crucial components of riverine landscapes (Tockner and Stanford, 2002). They are important areas for biodiversity and contribute to a broad variety of ecosystem functions by controlling the regional water cycle and the retention and transformation of nutrients in river systems (Weigelhofer et al., 2015, Sanon et al., 2012, Schindler et al., 2014). Their importance in fluvial landscapes is related to the high spatial heterogeneity in concert with a high and flood-driven temporal variability (Tockner et al., 2000). These dynamic fluvial processes are responsible for habitat succession and rejuvenation (Hohensinner and Drescher, 2008), leading to a high biodiversity along aquatic – terrestrial boundaries (Bunn and Arthington, 2002). Lateral hydrological connectivity, defined as the water exchange between floodplain and river, is the key determinant of water-related ecosystem processes such as nutrient turnover, vegetation development, and geomorphic change (Amoros and Bornette, 2002, Hein et al., 2004, Schoenbrunner et al., 2012, Welti et al., 2012).
Although there is a wide appreciation of the ecosystem services provided by floodplains and their vital role in riverine landscapes (e.g. Posthumus et al., 2010, Sanon et al., 2012, Schindler et al., 2014), there have been dramatic losses of floodplain habitat due to land reclamation and channel engineering, resulting in a functional degradation of these systems worldwide (Tockner et al., 2010). The reduction and degradation of floodplain systems has diminished their capacity for water retention, thus enhancing flood risks (Habersack et al., 2015), while other key floodplain functions and services, such as groundwater replenishment, nutrient storage (Hein et al., 2004), and water purification have also declined in effectiveness. The dramatic loss of riparian ecosystems threatens the conservation of key species and habitats, such as pioneer plants and soft- and hardwood tree species of alluvial forests (Scholz et al., 2012) and the aquatic vegetation of backwater systems (Keruzore et al., 2013).
These problems are particularly acute in the case of the Danube. With a length of approximately 2800 km, the Danube crosses 15 countries from its origins in southern Germany to its confluence with the Black Sea (Romania). It drains a catchment of approximately 801,100 km2 linking different natural and cultural landscapes and shaping the history of the region like no other European river (Tockner et al., 2009). Human culture and development have greatly affected the Danube River and the surrounding landscapes. Over the last century, the floodplains of the Danube and its tributaries have been subject to major human interventions causing significant changes in the hydromorphology of the river-floodplain ecosystem (Hohensinner and Drescher, 2008). The increasing demands for land for settlement and agriculture have resulted in large-scale river regulation measures for flood protection, forcing the river into a single, spatially restricted channel between extended dams. About 39% or 1111 river km of the entire Danube are impounded by a total of 78 dams (ICPDR, 2009). As a result, more than 68% of the active floodplains of the Danube River, which are in frequent exchange with the main river channel, have already been lost (e.g. Danube Pollution Reduction Programme (DPRP), 1999, Schwarz, 2010, Tockner et al., 2009). The consequences of these changes are predictable, and include an increase in serious flooding in different regions of the catchment, an increasing pollution load due to continuing emissions and reduced retention capacities, the loss of physical habitat diversity, and a correspondingly high percentage of endangered riverine species (ICPDR, 2009). Taken together, the Danube River Basin is therefore among the most pressurized large river catchments in the world (Tockner et al., 2009).
An improvement of the current status of residual floodplains through the basin-wide application of restoration measures is one of the key water management issues identified in the Danube River Basin Management Plan (DRBMP; ICPDR, 2009). The political changes in Central and Eastern Europe and respective EU policies (EC Water Framework Directive, EC Floods Directive, EC Habitats and Birds Directives; Council of the European Communities, 1992, Council of the European Communities, 2000, Council of the European Communities, 2007) are fostering efforts to protect the remaining Danube floodplains and restore the former hydrological dynamics by re-connecting floodplains with the main river. In addition, the 1975 Ramsar Convention on Wetlands (www.ramsar.org) supports the further conservation and restoration of floodplains and was instrumental in securing early protection for some examples of Danube floodplain wetland.
This paper presents the current status and the development perspectives of floodplains along the Danube River and its major tributaries. Based on the assessment of the overall restoration potential of Danube floodplains, we (i) present case studies from the Upper and Lower Danube to compare different approaches, (ii) assess the potential of various restoration measures to improve floodplain conditions, considering local drivers, obstacles, and opportunities, and (iii) address societal aspects concerned within the Danube River Basin.
Section snippets
Current state and restoration potential of floodplains in the Danube River Basin (DRB)
Assessing the restoration potential of Danube floodplains with respect to their current state and various pressures in the different reaches of the DRB is one of the pre-requisites to support and stimulate restoration projects. The first comprehensive and systematic evaluation of existing floodplains along the Danube and in the lowland parts of its major tributaries was commissioned by the UNDP/GEF as part of the Danube River Pollution Reduction Programme (Danube Pollution Reduction Programme
Austrian Danube floodplains between Vienna and Bratislava
The 45 km river stretch between Vienna and Bratislava is located within one of the last free-flowing sections of the Upper Danube River (Danube Pollution Reduction Programme (DPRP), 1999, Reckendorfer et al., 2005). Large-scale river regulation measures in the 19th century, designed to improve navigation and flood protection, have resulted in the isolation of the once extensive and dynamic floodplains from the main river channel and their degradation to a chain of decoupled floodplain remnants
New approaches in flood protection
River engineering to increase flood protection is one of the main reasons for the dramatic loss of floodplain areas in Europe (Hohensinner and Drescher, 2008). Until the end of the 20th century, flood protection consisted of the construction of dams and levees to retain flood water within the channel and thus prevent flooding of terrestrial surroundings. However, after the severe floods in Europe at the beginning of the millennium (Willi and Eberli, 2006, Barredo, 2007, Habersack et al., 2014),
Conclusion
While the assessment of restoration potential clearly demonstrates the existence of large areas with a high potential for restoration, critical gaps remain in the implementation of restoration projects, highlighting the limitations posed by stakeholder needs, public acceptance, and resource availability. Including these factors alongside assessment at smaller spatial scales might improve the understanding of which factors are crucial for floodplain restoration under different environmental and
Acknowledgments
The DANCERS project received funding from the European Union's Seventh Programme for research, technological development and demonstration under grant agreement no. 603805.
The project GWVLOBAU was funded by the European Agricultural Fund for Rural Development LE 07-13 under the grant agreement 323A/2010/043.
References (86)
- et al.
The impact of surface water exchange on the nutrient and particle dynamics in side-arms along the River Danube, Austria.
Sci. Total Environ.
(2004) - et al.
Optimised management strategies for the Biosphere reserve Lobau, Austria — based on a multi criteria decision support system
Int. J. Ecohydrol. Hydrobiol.
(2006) - et al.
Restoration ecology of riverine wetlands: 3. Vegetation survey and monitoring optimization
Ecol. Eng.
(1996) The Water Framework Directive: total environment or political compromise?
Sci. Total Environ.
(2008)- et al.
A framework for the assessment of ecosystem goods and services; a case study on lowland floodplains in England
Ecol. Econ.
(2010) - et al.
Quantifying ecosystem trade-offs: the case of an urban floodplain in Vienna, Austria
J. Environ. Manag.
(2012) - et al.
Large-scale controls on potential respiration and denitrification in riverine floodplains
Ecol. Eng.
(2012) - et al.
Connectivity and biocomplexity in waterbodies of riverine floodplains
Freshw. Biol.
(2002) Geografia Văii Românești
(1969)Major flood disasters in Europe: 1950–2005
Nat. Hazards
(2007)