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

G Borics et al: Water bodies in Hungary - an overview of their management and present state

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in valley dammed reservoirs and artificial pond systems on an area of cca 25,000-30,000 ha. By far the most important fish species produced in aquaculture in Hungary is the common carp (Cyprinus carpio) and the most important supplementary species are the silver carp (Hy- pophthalmichthys molitrix) and the grass carp (Cteno- pharyngodon idella). Species with relatively low contribution are the pikeperch (Sander lucioperca), the Northern pike (Esox lucius), the European catfish (Silurus glanis), the tench (Tinea tinea), the bighead carp (Hy- pophthalmichthys nobilis) and some other, especially Cyprinid or Pereid species. Unfortunately, many fish pond systems are age-worn and especially their sluicing is inappropriate to prevent the escape of cultured fish into natural habitats. This yields the escape of non-native species to natural stream segments. Reservoir dams also cause the fragmentation of stream segments. Therefore, one of the greatest challenges of environmental management in future decades will be balancing between multiple ecosystem services including water retention, fishery production, recreational fishing, and biodiversity conservation while also maintaining good ecological status in stream-reservoir systems.

Kisköre Reservoir

Kisköre Reservoir is the largest artificial lake in Hungary. The first dam on the Hungarian stretch of Tisza was constructed in 1954 at Tiszalök. The second water barrage system with the Kisköre Reservoir was built between 1967 and 1973. By damming up the section between Kisköre and Tiszavalk, Kisköre Reservoir has been established in the middle stretch of the Tisza, which with its 127 km' extension has become the second largest stagnant water of the Carpathian Basin. This reservoir was built for a power station and as a source of water for irrigation. Beside these, it functions as an important bird refuge and nature protection area (Fig. 15).

Figure 15. Kisköre Reservoir (nature reserve area)

The form of the recent image of the Kisköre Reservoir is the result of a longer process, which created isolated water bodies within the system differing sharply from each other in appearance, hydrological and hydrobiologi- cal features. Looking at the Kisköre Reservoir from an ecological point of view it can be considered as a shallow-lake type reservoir, of which large scale mosaicity is well represented by marshes, shallow-lakes, water pits excavated by floods, large and medium sized small water courses.

Changes of environmental conditions cause qualitative and quantitative changes of planktonic and benthic

elements of the flora and fauna. Because the concentration of plant nutrients in the Tisza river is high, main limiting factors of phytoplankton are the temperature and the suspended solid content. Annual changes of the latter variable can be linked to floods. In flood periods low number of species and individuals is typical. In summer the composition of the plankton is similar to that of other large reservoirs both in terms of number of species and individuals. Benthic fauna of the reservoir can be considered relatively rich in species. Dominance of stagnant water fauna is typical. Similarly to plankton the benthic flora and fauna shows pronounced differences among the basins of the reservoir. Currently about 50 % of the total reservoir surface is covered by plants. In waterweed vegetation of the reservoir water chestnut and in the marshy vegetation reed are stand-forming. Kisköre Reservoir with its diverse natural surroundings is an all- season fishing paradise with high catch rates. It has a wide variety of water depths, the zigzagging canals and the calm water of the reservoir provide ideal habitat for different kinds of fish. Most native Hungarian fish species can be found and relatively easily caught here.

Ecological state of the reservoir is continuously monitored by the water authorities. The filling succession of the reservoir basins is controlled by dredging and cutting of the macrophytes, thus the operation of the reservoir and its services are sustainably ensured.

DISCUSSION

Although there are many evidences that human activities in the Carpathian Basin had pronounced impact on the waters even in the medieval period, the comprehensive alteration of rivers and lakes started only in the 19th century. The huge wetlands that covered approximately 20% of the Great Hungarian Plain were drained, water level of the large lakes i.e. Lake Balaton, Lake Fertő were stabilised. The large rivers Danube, Tisza and each of their tributaries were regulated and an extended network of channels and embankments were established to satisfy the demands of safety, and the new agriculture, industry and trade. By the end of the 19th century the existing water network had been developed and successfully managed from hydrological point of view, but especially from the second half of the last century the growth of industry, the industrialised agriculture, the overuse of waters resulted in serious pollution in lakes and rivers, which frightened and destroyed the health of the ecosystems and jeopardized the rational use of water resources. As it was shown above solution of these problems required measures that were specific to the type of pollution and to the type of water bodies. Due to these efforts quality of the surface waters has greatly improved in Hungary. However, a number of problems have not been solved yet. The global warming results in several problems i.e., unpredictable precipitation regime and thus water level fluctuation in lakes and rivers, or invasions of alien species both plants and animals that not only endanger the elements of the native flora and fauna, but can cause serious water quality and health problems. These factors mean a great challenge for water management in the near future.