Metal Distribution in Forested Ecosystems in Urban and Rural Northwestern Indiana
1978
Parker, G. R. | Mc Fee, W. W. | Kelly, J. M.
Metal distribution in vegetation and soil components, annual inputs, and losses were determined in undisturbed urban and rural ecosystems in northwestern Indiana. The urban area has been exposed to contamination from industrial and other urban sources for about 100 years. The levels of cadmium, zinc, copper, and lead (Cd, Zn, Cu, and Pb) were significantly higher in the soils and vegetation on the urban site compared to a similar system in a rural setting 67 km away. Metal concentration in the top 2.5 cm of soil averaged 10 ppm Cd, 2,456 ppm Zn, 463 ppm Pb, and 119 ppm Cu. This was 20 to 100 times more concentrated than that found on the rural site. The surface litter (O horizon) on the urban site also had four to nine times greater metal concentration and total metal quantities were many times greater in the urban ecosystem than on the rural site. The higher soil levels were reflected in higher concentrations in most plant species, but species differed greatly in metal levels. Greater than 95% of the weight of all four metals was found in the soil (0–25 cm) for both dune and wetland ecosystems. The remaining metal burden is equally distributed between the surface litter and the plant biomass. Slightly more Cd and twice as much Zn entered the urban site than the rural site during 1975–76. Annual input of Pb and Cu was four times greater on the urban site. While pollution control has apparently reduced annual input to the urban site, metal concentrations will remain high due to the low rates of leaching losses measured.
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