Zs. P. Komáromy szerk.: Studia Botanica Hungarica 16. 1982 (Budapest, 1982)
Hably, Lilla: The relation between Pb-pollution along mainroads and the trace element-composition in soil and vegetation (Examination of section rectangular to M3 mainroad)
our sections are measured on a neutral pH-axes. The metric scale does not refer to the depth of the soil, - all starting from the surface, but indicates only their relation to each other on the pH = 7. In Fig. 11 the sections are shown in their original position, starting from the surface with the line of the neutral pH marked. Upwards from this the pH is acidis downwards it is alkaline. The pH-line demonstrates best the character of the "road-effect". It can be seen that the road unbalances the acidic and alkaline intervals, "drawing" the alkaline pH up to a higher level than it was. Its effect on the two sides of the road is not even. At the side of the section No. 30, the original balance is regained relatively nearer to the surface (at a depth of 60 cm). Section No. 34, which is about 106 m from the road, is regarded intact. At the other side of the road (in the wall of hole No. 36), this effect can be observed much deeper. At 35 meters from the road there is no equipoise at the depth of 120 cm. Where it sets in at this side, can not be observed, because of the absence of further sampling. It is to be seen that in the close neighbourhood of the road, alkaline pH can be found, already on the surface. Neutral pH surfaces are so high here that their presence can actually be excluded. III. Conclusion The road effect on the chemical reaction, trace element composition of the soil, as well as the relations there of to the parameters examined, and to the vegetation with special regard to lead content. The recognition of the effect of the road on the pH and the pH curve thus obtained will be the basis of the further explanation of all the results. As it was mentioned in Chapter II. 4. in the vicinity of the mainroad, the soil turns alkaline in a wide and deep zone (Fig. 11). The reason for this alkalization is certainly caused by the "road effect". There must be several factors contributing to this. The most effective alkalization is the consequence of the sprinkling of salt on roads in winter, when man introduces a very great amount of Na + into the soil. The asymmetry of pH = 7 curve shown in Fig. 11. Should be put down to the fact that the deeper side - received Na + then can be ascribed the road shows inclination upwards, and the grassy patch of the northern side lies somewhat deeper than the other side - or there were such differences in the composition of the soil, as facilitating the sinking of Na + into a deeper level. The verification of these suppositions needs further experiments. The alkalization occuring through the effect of salting is a doubtless fact. This can be regarded as a primary effect, which upsets the pH-balance of the soil and causes further equilibrium disturbance. Fig. 11 presents our sections at their normal right from the surface of the soil downwards, indicating the points, where carbonate content appears. It is to be seen that this level greatly varies even with relatively near sampling places. No. 36 contains carbonate already at the surface, while section No. 37 at a distance of 15 m is free from carbonate till the depth of 60 cm, at a distance of 20 m in section No. 38 carbonate mineral can be found only at a depth of 140 cm. In normal cases such extremes can not occur. Placing our sections on neutral pH (Fig. 10), the carbonate containing levels - logically -, fall to the alkaline interval. This can be clearly seen in Fig. 11 which presents the course of the pH-curve. From about a depth of 60 cm original carbonate content can be found, which accompanied the soil formation, this is shown by sections No. 32, 33. On the far side of the mainroad, where the pH = 7 curve slopes, carbonate can be observed only at a depth of 140 cm. The carbonate in the upper layers of sections No. 31 and 36 is probably a later effect, that is the results of a posterior precipitation in addition to the alkaline pH produced by the road effect. This supposition is supported also by the derivatographic examination (Chapter II. 2.), which indicates these precipitations appear at lower temperatures with endothermic peaks. This was experimented in the above two sections, and more marked calcitepeaks were observed only with deeper layers which is the result of carbonatification produced by natural circumstances in the process of soil formation. The change of the pH in such direction explains enrichment level of the soluble trace elements. Using the figures, in Fig. 11 those levels were marked which yielded higher trace element concentration after EDTA-shaking in relation to the total of all the trace elements examined. In Fig. 11 most of the values fall within.
