Vízügyi Közlemények, 1982 (64. évfolyam)

3. füzet - Botond György, Dobolyi Elemér, Gelencsér Péter, Györké Olivér, Jolánkai Géza, Szabó Sándor és Tóth László: A BALATON VÍZMINŐSÉG-SZABÁLYOZÁSA

396 Botond Gy., Dobolyi E.. Gelencsér P., Györké O., Jolánkai G., Szabó S. és lót h L. 2. Exploration of the processes affecting water quality in Lake Balaton 2.1. Factors affecting water quality within the lake by L. 10 W The chemical water quality of Lake Balaton has been studied at VITUKI regularly since the mid-fifties. The biological methods of study, referred to as "biological water classification" have been developed by the early seventies (Felföldi 1972/b). The method of biological water classification has acquired an importance comparable to that of the hydrochemical analyses, because it enables us to detect even minor changes of different nature in water quality. As regards artificial autrophication and thus also artificial eutrophication in Lake Balaton, the author claims the determination of phosphorus- and nitrogen forms to be among the most important investigations. As a first result of research, the pattern of P-forms in open water, in the shore belt, as well as in the sediments has been explored. The data obtained have been used for compiling the phosphorus balance of Lake Balaton (Fig. 14). Besides phosphorus, the trophity of lakes is controlled primarily by the amount and biological availability of nitrogen. For this reason, in order to gain a better understanding of the N-balance in Lake Balaton, studies have been started to determine the N-forms in the water and atmospheric precipitation, further on the biological N

2-combinations (Fig. 15). The author attributes particular importance to the investigations in the shore belt, primarily on the methods of hair-weed control and on the role of reed stands. Human water uses (recreation, bathing, sailing) are definitely disturbed by the hair-weed, but the large mass of weed rooted to the bottom tends to hinder algal prolification by its shading effect, further by absorbing the mineral salts on which any plant life depends. By photosynthesis the weeds produce oxygen, accumulate in their mass a variety of pollutants, so that their overall effect on water quality is a beneficial one. The studies on the reed stands have revealed these to be the largest biological filter in the shore belt of Lake Balaton. Dependig on the rate of loading the reeds are capable of accumulating growing amounts of the substances entering the lake. The reed stands around the effluent discharges absorb greater quantities of the biogenic elements than in the unpolluted areas. 2.14. Sediment-water interaction by Dr. P. GELENCSÉR According to the author round 95% of the external phosphorus load discharged to the lake is retained in the system and accumulated eventually in the bottom sediment. In the course of the complex biochemical and physico-chemical processes in the water-sediment boundary layer, part of the phosphorus content is mobilized into forms available to the aquatic plants. This phosphorus emission is referred to as the internal load. Under a study project extending to the entire surface area of Lake Balaton the chemistry of the top sediment layer has been determined. No typical variations along the longitudinal lake axis have been detected. The phosphorus content was found to be distributed fairly evenly over the depth of the sediment layer investigated, whereas the analyses of pore water have revealed high dissolved, reactive phosphorus concentrations, calling attention to the potential role of the "internal load". 2.2. External load entering Luke Balaton 2.21. The plant nutrient load discharged with sewage by Dr. E. DOBOLYI In estimating the plant nutrient load entering Lake Balaton, one of the most important problems was to determine the amounts of plant nutrients discharged directly into the lake, or indir-