Reconstruction of Danube-Habitats in the machland 1715-1991

The present 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 present 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 aquaticerrestrial 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.

The Machland research project was designed to reconstruct the original environmental conditions in the Machland Danube river landscape (Upper/Lower Austria) prior to river straightening (1715 - 1826) and to analyse the impacts of human-induced changes (1826 - 1991). The results of the project demonstrate the highly dynamic nature of the complex river channel network and the floodplain. These dynamics altered the living conditions for the floodplain vegetation on a regular basis and led to the dominance of shrubland and softwood forests. With respect to the fish ecological conditions, the original river system favoured fish species that prefer gravel-bed river channels with high flow velocities. The floodplain adjoining the main channel was frequently flooded and eroded, enabling intensive agricultural land use only in the more remote areas at the margins of the Danube floodplain. River engineering measures that were carried out to improve navigation in the 19th century and hydropower plant construction since the 1950s largely stabilised the river landscape. As a consequence, the original fish and vegetation communities typical for the Danube River gradually decreased. Today, the drastically changed environment is reflected by the dominance of older vegetation development stages and by fish species that tolerate the lower flow velocities in the dammed Danube River. In contrast, agriculture benefited from the river straightening measures, intensifying land use in the more central parts of the floodplain near the main channel. The results of the Machland research project have already been used in the "Leitbild"-discussion of ecologically appropriate river-floodplain restoration measures in similar river sections of the Austrian Danube River. They have also served in the pre-definition of biological reserves (NATURA 2000). Moreover, this research project enables new insights in the fields of environmental and local/regional history, shedding light on the socio-economic development of river landscapes over 300 years, and provides valuable data for various educational purposes (exhibitions, presentations, teaching aids, ).