Vízügyi Közlemények, 1999 (81. évfolyam)
1. füzet - Horváth L.-Tevanné Bartalis É.: A vízkémiai viszonyok jellemzése a Duna Rajka-Szob közötti szakaszán
A vízkémiai viszonyok jellemzése a Duna Rajka-Szob közötti szakaszán 81 köz area. This is due to the multiple effects of the series of river dams, which were built upstream in the Austrian and German river reaches and to that of the Gabcíkovó power station of the planned Gabcíkovó (Bös)-Nagymaros river dam complex. Research into the water quality of this region forms an important part of the ecological investigations of this area. Relatively long homogenous hydrological and water quality records are available for the area. Water quality issues became even more important due to economic changes and to the recent development of the science of this field. The water quality of the River Danube at the Hungarian/Slovak border is defined by the joint effect of upstream pollution loads in German, Austrian and Slovak territories and to the impacts of technical measures and establishments, such as river dams and waste water treatment plants (Table /.). As the result of the integrated effect of all these factors parameters of organic constituents and plant nutrients have shown in the period 1988—1995 certain improvement over the Danube section r.km 2204—1873. Long term changes of water quality of the Hungarian border station Rajka (r.km 1848) were investigated with the trend analysis of quarterly averages (1977-1996), while short term variation was revealed by the time series analysis of monthly averages of the period October 1992-October 1996. The analysis of the time series of annual average values was also carried out. Periodicity of the standard deviation dominates the variation of dissolved solids (conductivity, Fig. I.), calcium (Fig. 2.), potassium (Fig. 3.) and nitrate (Fig. 4.), unambiguously indicating the effect of hydrometeorological factors. Time series analysis of organic pollutants, characterized by chemical oxygen demand (COD C r and COD M n, Figs 5. and 6.) revealed alternating periods of rising and falling trends. Substantial load of organic pollutants of the seventies in the area upstream of the station investigated was followed, with certain time lag, by the expansion of waste water treatment capacities. This is well indicated by the trends revealed in the time series. Variation of trophic levels, indicated by the concentration of plant nutrients and their trends, depends not only on the external pollution load of the water system but also on the algae growth within the river. This latter was substantially influenced by hydrometeorological factors and by the changes of the morphological conditions of the river (Figs 7-9). The water of the Rajka station is potentially eutrophic-polytrophic. The time series of the quarterly averaged values of dissolved oxygen, indicating the combined effects of physical, chemical and biological processes, is shown in Fig. 10. Variation of pH and total suspended solids are shown in Figs 11. and 12. In the period after the commissioning of the Gabcíkovó (Bös)-power station (Oct. 1992-Oct. 1996) larger changes (exceeding 10%) was revealed, on the basis of the time series of monthly averages, only for iron, ammonium ion (decrease of 43%/year) and total phosphorus (22.8%/year). Annual fluxes of pollutants at Rajka are shown in Figs 13—14. For the river section between Rajka and Szob the changes of water quality followed similar trends as that revealed for the Rajka station. Among micro pollutants the concentration of mercury has shown substantial spatial and temporal variation. High mercury concentration values (Table II.) characterized the period 1977—1979. Data of the period 1989-1990 of the river reach Rajka-Szob indicated improvement in heavy metal pollution and can be considered tolerable. 90% duration values (considered as the basis of water quality classification in the relevant Hungarian standard) of the 20 year period 1977-1996 (Table 111.) indicate slow changes of the buffer capacity of the river water (pH increases, calcium ion slightly decreases, while electrical conductivity, the measure of dissolved slats, increased by more than 5%. These changes are due to the combined effect of changes of pollution loads from the right-bank-side and left-bank-side drainage basins, as well as to hydrometeorological and morphological changes. Along the reach of 140 km length the concentration of organic pollutants and ammonium ion are increasing and nitrate enrichment is also observed. Algae biomass is doubled along the reach, while orthophosphate concentrations are decreased by 20%. Variation of DO saturation percentage (-3.9%) between Rajka and Szob indicates the substantial self-purification capacity of the river.
