Vízügyi Közlemények, 1980 (62. évfolyam)

2. füzet - Joó Ottó-Lotz Gyula: A Zala folyó szerepe a Balaton tó eutrofizálódásában

A Zala folyó szerepe 255 The observations concerned with eiitrophication in Lhe lake are described in Part 1 of the paper At the mouth of the Zala Hiver the observations on streamflow, Lhe suspended solids and

vnutrients (nitrogen, phosphorous) entering the lake have been conducted lor the past four years with daily frequency. The results of these observations are compared with the nutrient discharge resulting from the concentrated wastewaters originating in the entire catchment area. From the results it is concluded that round two-thirds of the nutrients entering the lake are not of concentrated origin, I heir majority finding access to the waters with floods during discrete high-water periods. Pollution is traced back to urbanisation to concentrated industrial and agricultural operations, the growing use of chemical and to the environment polluting effects of rising standards of living. These are identified as the main causes of eutrophication in Lake Balaton, rather than the sediment discharged by the Zala Hiver. As a consequence of eutrophication the quality of water in Lake Balaton deteriorates at a high rate, so that the western basin may become unfit for bathing within a decade. For Lhe comprehensive development of water management in the region a program has been drafted, lhe realisation of which is scheduled for ПО years. To gain the time necessary for the implementation of this program, the rate of quality deterioration must be retarded. In the interest thereof is it suggested to create a reservoir of many million cubic metres volume, 75 sq. km surface area and 1.4 m average depth over the downstream section of the Zala River. The substances detrimental to the lakewater and conveyed by lhe Zala Hiver would thus be intercepted by retaining lhe river flow in the area known as the Kis-Balaton marsh. The history and evolution of the Kis-Balaton marsh area are outlined in Part 2 of the paper. In Part summarizing the results of lliis investigation, it is concluded that by realizing the solution suggesled, lhe former Kis-Balaton marsh would be restored in a form adjusted to modern conditions. As a first stage of remedial measures, the marshy area is expected to prevent most of the suspended, organic and nutrient pollutants of the Zala River from entering Lake Balaton and to retard in this way the rate of eutrophication. * * * Itole de la rivière Zala dans l'eutrophisation du Lac Balaton Joó, Ottó et Lötz (iyula. ingénieurs Le lac Balaton, d'une superficie de presque 000 km

2, lac à eau peu profonde, le plus grand de l'Europe, important au point de vue touristique, est situé au centre du territoire de la Hongrie, à l'ouest de Danube. Son affluent le plus grand est la rivière Zala, ayant un bassin versant de 2622 km

2. Le bassin hydrographique total du lac est de 5774 km

2 (Voir figure 1). La première partie de la présente étude expose les mesures relatives à l'eutrophisation du tac. A l'embouchure de la Zala le débit ainsi que les matières en suspension et les substances nutritives azote et phosphore sont mesurés depuis 4 ans, avec une fréquence journalière. Les résultats de ces mesures sont comparés avec la charge de de substances nutritives provenant des aeux usées concentrées à partir de bassin versant entier. Il apparaît de là que deux tiers environ des substances nutritire entrant dans le lac ne sont pas d'origine concentrée la majeure partie d'eux entvant dans le lac avec des crues à l'égal de l'hydrogramme d'une crue. Les pollutions sont les conséquences de l'action polluant l'environnement de l'urbanisation, de la concentration industrielle-agricole, de l'utilisation excessive de produits chimiques et de la civilisation. Ce sont là les causes principales de l'eutrophisation de lac Balaton et non pas les alluvions de la rivière Zala. La qualité de l'eau du lac Balaton se détériore, pas suite de l'eutrophisation à tel point que son bassin occidental risque de devernir impropre au bain en moins