Reconstruction of Original Habitat Conditions of the Danube River/Floodplain Biocoenosis based on the Morphological Development from 1715 ¿ 1991 (Machland, Upper/Lower Austria)

The project reconstructs the original habitat conditions of the alluvial Danube River landscape in the Machland, Upper/Lower Austria. The primary goal is to deepen our understanding of the complex fluvial dynamics and the principles of hydrological connectivity within the river-floodplain system. Further, the natural situations from 1715-1821 will be compared to the conditions after river straightening (1832-1925) and construction of power plants (1991). The complex ecological interactions will be analysed using an integrative approach involving river morphology, vegetation- and fish ecology, as well as cultural landscape use. Today no stretches of the Austrian Danube River remain in a natural state. Detailed information on the original morphology and the floodplain ecosystem is therefore largely missing. The project is designed to define biotic and abiotic parameters in the sense of river-type-specific reference conditions for future protection concepts and restoration measures in the alluvial stretches of the Austrian Danube. This approach will also yield valuable baseline data for assessing the "ecological integrity" of such habitats. A total of 41 historical surveys of the former river landscape are available, enabling detailed analysis of the natural hydrodynamic processes prior to river straightening (1826), both over short intervals of a few years and over longer, decadal periods. In a first step, the original morphological conditions will be reconstructed two- and three-dimensionally based on historical sources with the aid of CAD/GIS. Apart from parameters of planform, cross-section and the longitudinal profile, also areas and volumes of sedimentation/erosion as well as aquatic/terrestrial interfaces will be determined. Based on area calulations, original habitat conditions will be modelled on the meso-habitat level, including qualitative and quantitative aspects. The analysis of historical terrain elevation will permit conclusions to be drawn on connectivity, network development and expansion/contraction of the water surface area. This information will be used to reconstruct the original fish ecological conditions (e.g. species diversity and dominance) on a general level. The historical terrain elevations also allow the former site conditions of the floodplain vegetation to be determined. Finally, the analysis of the river dynamics can help document the colonisation potential of unvegetated areas, development stages and successional sequences. These parameters will then enable the spatial distribution of the plant associations to be modelled using GIS. Investigations on the Danube region as a cultural landscape will underline the influence of socio-economic factors on the river-floodplain system.