The aquatic macrophyte vegetation in the Old Danube/Hungarian bank, and other water bodies of the Szigetköz wetlands

Abstract

This is a descriptive account of the impact of the Gabcikovo hydro-electric power plant (HEP) and other man-induced changes on the aquatic vegetation of the Szigetkoz area. Today the environmental complex of water bodies in the Szigetkoz supports 26 aquatic macrophyte species, which occur in the main river channel, and in different flood plain habitats. Prior to the construction of the Gabcikovo HEP almost no macrophytes existed in the main river channel. The HEP takes in most of the water today, reducing the discharge in the main river to a few hundred cubic-metres per second, compared with about 2000 m 3 .s -1 before. The water level has also decreased in the flood plain. Some parts of the channel and oxbow systems are irrigated through the complex Active Floodplain Water-Supply System (AFWSS), today. Several aquatic and amphiphytic species have invaded in the abandoned river bed and in shallow reaches with little flow or even stagnant character. Flood plain water bodies show a different successional development. In some side arm systems the lack of water has led to a near or full extinction of aquatic vegetation. Other parts, receiving compensation flow water by the AFWSS were transformed from marshlands to fully aquatic environments. Where algal production increased no macrophytes are present. Other water bodies have clear water, but only a few eutrophic species remain there, and in many survey units rare species have disappeared. A striking feature of the aquatic vegetation is the clumped distribution of many species: they develop large stands in some habitats, but they are not widely distributed over the whole water body system. The whole system is still in a state of change and the decrease in species richness may continue.