STATE OF THE ENVIRONMENT OF THE LAKE BALATON REGION
Lake Balaton is the largest freshwater lake in Central Europe. It represents one of the most important natural assets of the country. The location of the Lake Balaton region is extremely advantageous. It is situated in the Transdanubian region of Western Hungary, alongside the international highway connecting the capital city Budapest with the Adriatic sea.
Due to its very shallow profile and hydrochemical features Lake Balaton is very vulnerable to environmental degradation. Like for many natural ecosystems around the world, anthropogenic impacts are playing an increasingly important role in determining ecological status and dynamics of the lake.
Due to its geographical situation, the climate of Hungary is temperate with alternating Atlantic and continental influences. In the Lake Balaton region the normal mean air temperature is 10.7 ºC, the coldest month being January, the warmest July with –1 and 21 ºC mean temperatures, respectively.
Annual solar radiation of the region is 2,000 to 2,100 hour in a year. The maximum monthly total is about 800 to 820 hours from May to August. Yearly average precipitation in the region is 750 to 900 mm, and it is relatively higher than the Hungarian average. In the summer season rainfall events often occur locally, in particular, around the lake.
The most frequent and strongest winds on Lake Balaton blow from the north-west, at speeds averaging 3.2 m/s over the year. July is the windiest month with an average speed of 5 m/s, while the calmest months are in autumn. The number of storm days in summer is 15-20, with wind speeds higher than 15, but occasionally up to 45 m/s.
The winds are influenced in their force and direction alike by the mountains so that they strike the water from different directions and with different strengths. Along the northern shore the wind is highly turbulent, evening out and becoming stronger proceeding farther out over the water. Along with the winds, currents are influenced also by the shoreline configuration.
AIR- AIR POLLUTION
In the lake-side communities of LBRA, transportation is the major cause of air pollution, although the Lake Balaton Act (Act no. CXII/2000.) specifies stricter air pollution control measures in the whole region as compared to other areas of the country. The poor quality and service level of the transport infrastructure negatively influences the economic and social development of the region. It can be said that those small areas which are not located immediately on the shore of the Balaton are by far more underdeveloped and they are in a more disadvantageous situation.
WATER – HYDROLOGY
51 water courses flow into the lake, of which only 20 have permanent water discharge. The Zala river is the most significant, draining 45 % of the catchment area. Its average water discharge is 7 m3/s, therefore its role is significant not only in the water management of the lake, but also in forming its water quality. The Zala river delivers a significant part, one third of the total nutrient load to the tiny Keszthely basin of Lake Balaton.
The total area of the lake itself plus its catchment area is 5,775 km2. The Zala River drains an area of 2,622 km2 towards Lake Balaton. The sub-catchments of the minor streams on the southern and northern shores are 820 and 1,175 km2, respectively while the run off from 562 km2 finds access directly to the lake.
From a geo-historical point of view, geologists previously estimated that the age of Lake Balaton was 18-22 thousand years, dating its formation to the end of Pleistocene age. According to the latest research results, the present form of the lake developed 7-5 thousand years ago in the Holocene age. Thus Lake Balaton is a fairly young formation, not only in terms of geology, but also from a limnological point of view.
The catchment area of the lake (together with the water surface) is 5,775 km2. The catchment area can be divided into three units, the Northern, the Western (Zala river catchment area) and the Southern area. For various research purposes, the lake itself is divided into four basins, viz the “Keszthely”, “Szigliget”, “Szemes” and Siófok basin (from west to east). The lake surface at standard water level is 594 km2, its water volume is around 2 billion m3, and the average depth is 3.2 m.
The lake volume is influenced by the amount of evaporation and outflow, the amount of precipitation on and inflow to the lake. Direct use of lake water is negligible. The long-term average values of precipitation and evaporation are 626 and 914 mm respectively. Related to the entire lake surface, the inflow and outflow correspond to 968 and 680 mm respectively.
Around one-half of the inflow is discharged to the lake by the Zala river entering the south-western part of the lake. The major streams on the southern shore are the Western Interception Canal and the Keleti Bozót, in the northern shore the Lesence, Kétöles, Tapolca, Eger and Világos creeks. As already mentioned, for the purpose of hydrological studies the lake is subdivided into four basins. The basins increase in size from east to west, whereas the inflows decrease in the foregoing order. The major part of the inflow is thus discharged into the smaller south-western basin. The proportions of inflow volumes correspond exactly to those of the sub-catchment areas. The differences in the proportions of the inflow volumes and the basin volumes decisively influence the quality of water in the basins.
WATER QUALITY – EUTROPHICATION
The disappearance of the natural filter zone of Kis Balaton, together with the increasing emission of agricultural runoffs, industrial wastewater (food industry) and inefficient sewage treatment supported eutrophication processes in Lake Balaton by the mid 60’s, especially in the westernmost Keszthely basin. Critical water qualities during summers prevailed until 1994 and were characterized by unpredictable blooms of Cylindrospermopsis raciborskii, an invasive cyanobacterium of tropical origin.
A large scale restoration program aimed to restore the original ecological status of the lake was initiated in the early 1980s and later on it became the largest scale wetland conservation/restoration/management project worldwide.
Today discharges deriving from facilities working in settlements are gathered in the public sewer after necessary pretreatment, and are treated together whit municipal wastewater. Municipal waste management services are available in almost 100 % of the settlements, only a few small populated settlements are not involved in the public waste disposal network.
The restoration project also included the construction of the Kis-Balaton Water Protection System. Nowadays the reconstructed Kis-Balaton area together with the marshlands (traditionally called “berek” in Hungarian) of the southern shoreline is under the protection of Ramsar convention. The most important habitat of the Lake itself is the reed belt, which provide feeding and spawning habitats for fishes and also important as filtering zone.
The most typical soil in the catchment is leached brown forest soil, which is non-cacareous, 70 to 75 % Ca saturation, 50 to 60 5 base saturation, and slightly acidic (pH 6.2 to 6.8) and contains 250 to 350 mg – TP/kg. Approximately two third of the whole catchment area is covered by it.
Considerable portions of the northern and southern sub-catchments are covered by brown earth, of which characteristics are quite similar to those of the leached brown forest soil.
In the major part of the Keszthely Mountains and the South Bakony Mountains, the predominant soil is rendzina, which is usually calcareous and Ca-saturated with high organic matter content in the shallow humus horizon.
The Kis-Balaton, the Nagyberek, and the Tapolca Basin are peat areas. A main part of the Nagyberek was drained and ameliorated for an agricultural purpose in the 1950’s, conversely, the Tapolca Basin is protected as an ancient peat relict.
From the viewpoint of soil erosion, about 70 % of the northern sub-catchment is strongly eroded (more than 70 % of the original surface layer is eroded). Above all, almost all areas that are not covered by forest vegetation and are used as orchards and vineyards are strongly eroded. In the flatter southern sub-catchment the ratio of strongly eroded area is about 10 %. In addition to water erosion, the impact of wind erosion has become more and more significant, particularly on drained and ameliorated peat areas and sandy soil areas.
The catchment area of Lake Balaton is 5212 km2, nearly nine times larger than the lake’s surface area (593 km2). It is dominantly agricultural land. Elevation of the mildly rolling hilly landscape varies between 100 and 400 meters above sea level. About 62% of the land is in agricultural use, while 26% is forest. The catchment can be divided into three characteristic regions.
The northern catchment follows the shoreline of the lake in a wide band and represents about one-fifth of the total area. The streams (many permanent and temporal) draining this area are relatively short with high slope gradients. This land is the least suitable for agricultural purposes. Due to the topography and to the soil conditions this area is least suitable for plough land (row crops) and the forest land fraction is the highest here. The ratio of low value grass land is high here. Wine-grape plantations form the dominating agricultural use and they have special importance in regard to the water quality of the lake.
The area of the southern catchment is 1450 km2, about 1.5 times larger than the northern catchment. Streams flowing perpendicularly to the shoreline drain this area. There are marshes with groves along the near-lake area, where grass land and forestry are the dominating land uses. Forest soil underlain by loess form the area of the Marcali table land prone to erosion, along with the indented area of Külső-Somogy.
The area of the western catchment is about as large as the above two combined. The river Zala, draining this catchment, carries about half of the total inflow and total sediment load of the lake. These loads impact directly on the Keszthely Basin, which represents hardly one-twentieth of the total volume of the lake. The area is hilly with the exception of the Kis-Balaton and the surrounding marshy area. Soils of the area are prone to erosion, the more so since this area receives the highest precipitation