Hidrológiai Közlöny, 2016 (96. évfolyam)

2016 / 3. szám - HISTORICAL SNAPSHOT - Borics Gábor - Ács Éva - Boda Pál - Boros Emil - Erős Tibor - Grigorszky István - Kiss Keve Tihamér - Lengyel Szabolcs - Reskóné Nagy Mária - Somogyi Boglárka - Vörös Lajos: Water bodies in Hungary - an overview of their management and present state

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Hungarian Journal of Hydrology Vol. 96. No. 3. 2016.

Tourism and natural spots are important along the Danube. Also especially travel cruises and shipping transport on the river are of significance, especially on the frequented route between Vienna and Budapest. The Danube Banks in Budapest are a part of Unesco World Heritage sites; they can be viewed from a number of sightseeing cruises offered in the city. Despite extensive development of Hungary some of the original floodplain ecosystems survive (Fig. 1). Reminders of the primeval landscape, floodplain forests such as those in Gemenc area of Hungary provide habitats of birds, e.g. whitetailed eagle, black stork, black kite, night heron.

Figure 1. Danube River at Göd

Today, we should find the harmony between the shipping, drinking water and energy production, recreation needs - to mention only the most important ones - although these issues require different management approaches. One of the main problems is the establishment of reservoirs of the power plants, which hold the suspended solids and debris, and thus lower the river bed at the downstream sections, which hampers the water supply of Budapest. It can also be observed in Gemenc region where as a result of the decreasing water level, the side arms detached from the main channel and now form a typical backwater.

In the 1950s, '60s due to the industrial development and to the increasing use of agricultural fertilizers the Danube became enriched with nutrients. In the 1960-70s large-scale power plant dam construction programs began, which meant a drastic reduction in rolling and transporting suspended sediment. The suspended solid deposition resulted in improved light conditions, so in addition to the abundance of plant nutrient supply, significant eutrophication (algae) occurred (Kiss 1994, Kusel- Fetzmann et al. 1998). At the Hungarian section in 1980s the chlorophyll-a concentration was often larger than 100 pgL', and even the yearly average often reached or exceeded the 50 pgU (Fig. 2) caused mainly by centric diatoms (Kiss el al. 2012).

Figure 2. Changes of yearly average chlorophyll a concentration in Danube River at Göd, measured in the vegetation periods. Red

line indicates the good/moderate border

The values in the Szigetköz and Gemenc side arms sometimes reached 200-300 pgL1. After the political changes at the beginnings of 1990-es the industrial and agricultural production has fallen significantly, which considerably reduced the use of fertilizers. Thanks to the European Union Water Framework Directive a lot of big cities, municipalities developed an effective wastewater treatment. As a result of these actions, nutrient supply dropped to one third of the previous values and water quality of theDanube started to improve. The largest environmental investment implemented in Central Europe fundamentally modernised the wastewater treatment system of Budapest, ensuring cleaner waters for all those living along the banks of the Danube.

Although eutrofication of the river Danube successfully controlled, in the recent years increasing amount of evidences indicated that other forms of pollutions frighten the quality of the Danube. Various persistent micro-contaminants (drugs, pesticides etc.) which cannot be eliminated in the wastewater treatment plants have become the focus of interest. Increasing occurrence of non-native, invasive organisms means acute problem in the Danube river valley, because these taxa can be disease carriers or occasionally replace the elements of the native