Hidrológiai Közlöny 1977 (57. évfolyam)
1. szám - Egyesületi és Műszaki hírek
54 Hidrológiai Közlöny 1977. 1. sz. Dr. Literáthy Péter: A Sajó fenélcüledékében in the bottom sediment. Any change in turbulence conditions —e. g. at rising stages —may cause the bottom sediment to become stirred up. This is the reason why the bottom sediment enriched in toxic metals presents a continuous potential hazard to the stream. A number of metal pollutants are discharged into the Sajó River over its course in Hungary. For this reason the water analyses conducted under the Project have been supplemented by such on the bottom sediment and the results have been evaluated in combination. Drawing on several specifications and recommendations, the allowable concentrations of various metals in the Sajó River have been compiled (Table 1). An important section of research work was directed at obtaining a better understanding of the methodological problems. The way of expressing the results of analyses on bottom sediments presented a special problem, since the expression in mg metal/kg of dry sediment units, widely used in the international literature, may incorporate a considerable sampling error due primarily to the uncertain quantity of sand particles. Reproducible, pertinent results readily suited to comparisons have been obtained (Table 2 ) by relating the quantity of the pollutant to the sample fraction which is soluble in acids and is decomposed upon ignition, i. e., by introducing the new basis of reference, denoted by VA. The analyses on the metal pollutants present in the Sajó Kiver have shown mercury, cadmium and lead to cause the greatest hazards. The results of water analyses in some representative cross-sections of the Sajó River are illustrated in Figs. 1, 2 and 3. The streamflow- and suspended sediment conditions on the Sajó River will be appreciated by considering Table 3. On some sections settling, on others resuspension will be seen to predominate. From the results of water analyses the concentration of mercury is to be seen to attain already the allowable limit and to increase further over the section in Hungary. Lead and cadmium were found to settle at faster rates and to become stirred up less readily, but even so concentrations exceeding the limit values were detected downstream of the effluent discharges. The situation is especially grave over the central sections of the river, remembering that the toxic effect of these metal pollutants is additive. As revealed by the analytical results on bottom sediment, the metal content thereof is multiplied downstream of the major sources of pollution, as indicated in Fig. 4. For describing the potential hazard presented by the toxic metals in the bottom sediment, the volume of water becoming toxic by the resuspension of 1 g bottom sediment VA, or the inverse value thereof has been adopted. The situation at several points along the Sajó River, at different instants is illustrated in Fig. 5. Tn periods of greater discharges, during floods, the bottom sediments are picked up and tho pollutants are spread over larger areas. The potential hazards due to the two metals in the Sajó River downstream of the sources of lead- and mercury pollution arc illustrated in Table 4 at different instants. It is positively demonstrated that at times of greater streamflow rates the pollutants in the bottom sediment are removed to greater distances from the source of pollution, whereas at normal flow regimes accumulation is predominant. The same process for cadmium is indicated in Fig. 6, showing also the variations in streamflow rate during the period of analysis. Summarizing, it may be concluded that — the metal pollution after reaching equilibrium in the recipient water will be distributed between the dissolved and solid forms depending on the ionic environment of water, the solid form being potentially accumulated in the bottom sediment, — in particular studies the water analyses must be performed with great frequency, whereas 4 to 8 samples annually may also suffice in the case of bottom sediments, since the latter may be regarded the "memory unit" of surface waters which conserves the pollutants for extended periods of time. Thus it may become possible even before starting regular water analyses to arrive at conclusions concerning earlier pollutions from bottom sediment analyses; — bottom sediment analyses yield information to mass balance studies and for considering the effects of flood waves, beyond characterizing pollution. Automatikus vízminőség ellenőrző állomás Sajó püspök inéi VIZDOK foto: Körtvélyesi László
