Vízügyi Közlemények, 1989 (71. évfolyam)
3. füzet - Szilágyi F.-Szabó Sz.-Mándoki M.-Tóth L.: A műszaki beavatkozások hatása a Velencei-tó vízminőségére
450 Szilágyi F., Szabó Sz., Mándoki M. és Tóth L. в некоторой мере отрицательно влияли с точки зрения охраны природы. Согласно результатам исследований гидрохимического состояния, фито- и зоопланктонов, мозаичность озера значительно уменьшилась вследствие регуляционных работ берега и русла. Уменьшение трофичности по разному влиянию на отдельные части озера, оно было более заметно на восточной части озера (рис. 6). Здесь качество воды заметно улучшилось и стало более пригодным для удовлетворения рекреационным требованиям. * * * The effect of technical interferences on the quality of water of Lake Velence by Dr. F. SZILÁGYI, biologist, prof, of chemistry, Sz. SZABÓ, С. E., M. MÁNDOKI (Mss), biologist, prof, of geography, L. TOTH, A. E. Lake Velence became a favourite resort area due to its advantageous location and proximity to the capital of Hungary. Over the catchment of Lake Velence (Fig. 1) gradual social-economic development has been observed from the 60s (Fig. 3). Demand for recreation has also increased. At the same time, the processes of aging and sedimentation had sped up hindering the conditions of recreational use. Around the end of the 50s a grandiose program for development has been initiated with the guidance of the Executive Committee for Lake Velence to improve the usability of the lake for recreation. The Water Authority of Central Transdanubia had played the role of contractor. 80 percent of the work was executed between 1972 and 1987 (Table II). Regulation of the shores and of the lake-bed (excavation of sludge and reed, construction of bank protection, of harbours) was extended over a large part of the lake surface Fig. 4). 9 million m 3 of sludge had been taken off, 24 km long bank-protecting structures were constructed. Due to such technical interventions, the surface area of the lake has decreased by about 1 km 2. The character of the lake has been substantially changed. The ratio of open water to reed was increased from 41 percent to 57 percent (Table III). By investigating the origin of an increased nutrient load which is to promote eutrophization, the characteristics, the social and economic development, the waterhousehold of the lake, the chemical features of its water had been analyzed by the authors. Also, the hydrobiological progress reached during the past 20 years was taken into account. Through the water chemical parameters - with long duration and based on a great number of observations (Fig. 5) - the effect of technical interferences has been evaluated from the point of view of recreation. It was stated that the trophicity of the lake has been substantially reduced (Fig. 7). This was due to a thorough excavation of the soft bed-sediment consisting of a great volume of organic material, to a more favourable turbidity, and to the shading effect of a less favourable settling of the suspended load. It must be noted that recreational interventions in the resort areas were practically and partially unfavourable for environmental protection. According to quoted results of investigations in water chemistry, phyto-and Zooplankton biology and on living cover, the former mosaic nature of the lake was greatly altered after the bank-protecting structures were built and when the needed bed-regulation was accomplished. Reduction of trophicity exerted different influences on the individual parts of the lake. Changes were made expressive in the eastern parts. Here, the quality of water turned much more suitable for recreation. * * *
