Wetlands display a startling variety in geomorphology, hydrology, chemistry, vegetation and fauna. The objective of this thesis was to refine the definition and delineation of wetlands on the basis of the macrophyte vegetation, (2) to characterize shallow water bodies (oxbow ponds) and wetlands on the basis of macrophyte vegetation (cover, types, homogeneity, pattern and biomass), and (3) to survey and evaluate aquatic macrophyte assemblages from the aspect of nature conservation.

23 sites were included in the survey, providing 543 floristic data for 170 species (56% dicots, 41% monocots, and 2% pteridophytes). Habitually different vegetation types were identified in a set of wetlands, and macrophyte composition was evaluated on the basis of relative indicator values and other ecological classifications. In most sites the number of hydrophytes ranged between 8–12. The number of species associated with the hydric and littoral ecophases was shown to be a subtle indicator for the nature conservation value of these wetlands. On the average, the vegetation consisted of 4 community forming species, 14 associated spp. and 4 other spp. The ratio of associated species to skeleton species was found to be a relevant indicator of vegetation richness.

Fresh biomass of 11 macrophyte vegetation types was determined at several sites and dates (68 samples, 257 quadrats) by harvesting water monoliths. Biomass of macrophytes was found to be a sensitive indicator of year-to-year environmental changes which may be particularly marked in floodplains. A macrophyte cover over c. 70% of total water surface had a profound effect on the subordinate open water, resulting in an overall littoral (wetland) character. On the basis of water depth records from the macrophyte stands, hydric, littoral and limosal ecophases were clearly distinguished. However, in areas where large water level fluctuations, human interference, degradation of biota etc. dominated, stands of macrophyte species occured at any water depth within the observed ranges. In less disturbed situations and in the presence of each other they occupied more or less definite zones.

Total cover of macrophyte stands in oxbows of near-natural state was over 70% in mid-summer, dominated by floating-leafed aquatics, followed by emergents and submerged beds, with 20–25% of open water. This ecologically favored state can only be maintained by management for conservation per se, since extense macrophyte overgrowth generally hinders most forms of human water use.