Road transportation impact on the soil environment – trace metals migration range assessed by magnetic survey of soil

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Summary:

Policy of road transportation development in the countries of Central Europe imposes construction of new and modernization of existing roads for still increasing transportation burdens. Road transportation release broad range of chemical pollutants, including trace metals (Zn, Cu, Pb, Cd, Co, Cr, Ni, Cu). High concentration of some chemical elements may destabilize homeostatic balance of the soil environment and may decrease health of forest stands. Negative impact of trace metals depends not only on its concentration but also on a form as well as chemical activity of chemical compounds which include trace metals. Potential negative impact of trace metals on the soil environment can be assessed with utili-zation of magnetic soil survey methods. An easy-to-measure geophysical indicator of magnetic properties of some materials is magnetic susceptibility, which de-scribes the magnetic response of a sample when exposed to a weak increasing magnetic field and is directly linked to concentrations of ferromagnetic minerals. For example, if magnetic susceptibility over soil surface equals 30 to 50x10-5 SI units, it may be assumed that concentration of at least one trace metal goes be-yond threshold natural value for forest ecosystem soils. The aim of the research was assessment of spatial distribution of magnetic susceptibility of forest soils in the vicinity of the state expressway no. 11. Magnetic susceptibility was measured along 40 m transects established with utilization of land survey methods. The transect axis were perpendicularly oriented against verge of road section. The resolution of measurements was 0.5 m. The result of measurement for transect axis was an average value calculated out of 10 separate measurements. Vertical distribution of magnetic susceptibility was measured up to 20 cm b.g.s. Magnetic susceptibility of cores was measured in the cores with MS2F sensor (Bartington Instruments). The highest κ values were noted for the asphalt concrete road pavement layer which was constructed with material containing ferromagnetic minerales. In general, patterns of κ values vertical distribution at experimental site were similar to the distribution patterns typical for natural, unpolluted forest soils. Intensive migration of ferromagnetic particles into forest ecotone zones was not identified. Increased surface magnetic susceptibility was noted for the area stretching up to 5 m from the road surface verge. (κ values no less than 50x10-5 SI units). Farther away from the road verge (5 to 40 m) soil magnetic susceptibility did not exceed 22x10-5 SI units – average threshold value for natural soil magnetic susceptibility of forest areas in Poland. Vertical magnetic survey returned maximum κ values at depth 5 to 10 cm b.g.s. Suppressed concentration of ferromagnetic particles in soil under Silver Birch stands may result from the species capability to uptake and bioaccumulate the magnetic particles in assimilative organs.

Citation:

Czerniak A., Poszyler-Adamska A. 2009. Road transportation impact on the soil environment – trace metals migration range assessed by magnetic survey of soil. Infrastruktura i Ekologia Terenów Wiejskich. Nr 2009/ 05