Vízügyi Közlemények, 1993 (75. évfolyam)

3. füzet - Jolánkai Géza-Bíró István-Szász Rita: A Rajna-vízgyűjtő pontszerű és nem pontszerű szennyezésének vizsgálata

262 Jolánkai G., В író 1. és Szász R. 6). Results of the calculations include the hydrological and water quality (concentration and load) profiles of the river system, in graphical and tabulated form, and the areal distribution of non-point source pollution export rates, which latter can be visualized in digital-map form as well. This latter is the result which can be considered novel one in the case of the River Rhine. This is also very important, since upon the effects of substantial and efficient point-source control programmes carried out in the past decades, the diffuse load component makes up, in respect to many parameters, the bulk of the total annual load. For cadmium (Figures 7-9 and Table II) the calibration was made against the data of 1977, a year when this hazardous contaminant was still the source of serious problems. It was found that about 40% of the total cadmium load originated in that year from diffuse sources and these sources were concentrating around the large industrial agglomerations. Although this value is considerably higher than the 20-25% estimated earlier by others, the verification of the model against the data of 1988 and the 90% diffuse load component found for that year makes this model result highly probable. The more so since recent estimates by others are in good agreement with the 90% estimate of the SENSMOD run. Calibration and verification results of the phosphorus model (Figures 10-11, and Table 111.) were in full agreement with the estimates of the respective local literature, which report on the details of the phosphorus budget. Model runs were able to simulate the effects of the substantial reduction of point source loads, that had been made in the past decade, surprisingly well. Consequently the results of predictive model runs, based on the forecasts of further load reductions by the German- and International Rhine Commission, wich estimated a further 44,6% phosphorus load reduction by 1995 at the German/Dutch border section, can also be considered as probable ones. Although the verification attempt of the calibrated nitrogen model (Figure 12) failed, this can be also considered an indirect proof of the reliability of the model, since there were no point source load data of nitrate available and thus the self-calibration algorithm of the model considered identified all nitrate pollution as diffuse-source pollution. This led, eventually, to much distorted model parameters, which in turn prevented the verification of the model. Consequently the modelling result, in this case, was the finding that the reason of this failure was clearly the lack of appropriate measurement data on point source N loading, and that without appropriate measurement data no reliable model can be made. The results of the BOD model (Figure 13.), revealing the load and concentration conditions of biodegradable organic matter, highlighted some interesting features. It was found that eighth times as much organic load originates from diffuse sources than from the point sources, a rather unusual proportion. This can be explained in two ways: Either considerable quantities of organic matter are produced (by primary production) in the impounded reaches of the river system, or there is a large number of unmeasured point sources of pollution. Eventually the joint effects of these two type of sources can also give an explanation. Since the modelling results identified high diffuse loading rates of BOD in the vicinities of large urban agglomerations, and these rates were characteristically those of the urban stormwater runoff, the most likely explanation is that the pollution loads originating from the separated stormwater sewer systems of urban areas were not measured and thus were not included in the data bank of BOD point sources. The authors concluded the study with a belief that the results of this project have again given a proof for the wide applicability of the model system SENSMOD. Considering the study a successful one the authors recommended the continuation of the project towards their partners and other potentially interested institutions, stating that with more reliable and more detailed data the model could be brought to the level of a practical and comprehensive water pollution control decision support system of the Rhine River Basin. * * *