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Ecohydrology is more than just hydrology and ecology combined. It is functional to its best only, if science, engineering and construction, public administration and political decision assist each other in an integrated scheme and on a common scale. The UNESCO Biosphere Reserve “Lobau”, part of the Danube National Park today, is dependant on all four aspects for its sustained existence. The integrated water regime in Vienna, comprising the Danube river, the “New Danube” flood control channel, the Old Danube oxbow, and the water bodies of the Lobau, is presented here. Political decisions backing the efforts of engineers and biologists enabled the municipal administration to provide all necessary resources to keep the biosphere reserve in a healthy status. Finally outlines for initialising some aspects of ecohydrology in the Danube basin are presented.
The population structure of Phragmites australis (Cav.) Trin. ex Steud. was examined in seven categories of overgrowing flood control ditches, differing on time which had elapsed from the last clean-up. Density, biomass, frequency of development stages, as well as the size and habit of the shoots, were determined in the populations. Site conditions in the ditches and the proportion of the common reed in the total biomass of plants were also examined. The rate at which populations in cleaned ditches regenerate is very quick. Three years after the maintenance works in ditches the reed population is already fully regenerated. Well developed reed rushes, which biomass is about 650 g d.w.m⁻², are dominant. Its density amounts to 76 ± 25 shoots m⁻². Flowering and fruiting shoots are the most numerous. The first signs of population regression were observed in the ditches left without cleaning for more than 5 years. Population density is gradually lower, the proportion of generative shoots is reduced, and the reed is lighter and has smaller assimilation area. In the 11-year-old and older ditches the reed is replaced by other plant species, mainly grasses and shrubs.
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