Lead forms in Baltimore City soils under forest and grass

Ian Yesilonis, Center for Urban Environmental Research and Education
Bruce James, College of Agriculture and Natural Resources
Richard Pouyat, University of Maryland, Baltimore County
Bahram Momen, University of Maryland, Baltimore County

Lead (Pb) is a major pollutant from automobiles in urban ecosystems that deleteriously affects the health of living organisms. This study investigated the interactions of soil and Pb under two different cover types: forest and grass. The hypotheses are soils under different vegetation types will support different Pb forms. Secondly, there will be a concentration gradient from 10 to 50 meters from the road. Thirdly, more Pb will be in exchangeable forms and bound to the organic phase in forest patches than in grassed patches due to lower pH values and higher levels of organic matter, respectively. Six sites within Baltimore City, three forested and three grassed, mostly Alfisols, were sampled to 20 cm. by horizon at 10, 30, and 50 meters from the road. The forms of Pb were determined using the sequential extraction techniques developed by Rauret et al, 1989. The results show that cover has a significant effect on Pb forms (p< 0.01). There was no difference in Pb concentration at 10 and 30 meters from the road comparing cover types. However, at 50 meters a difference is reflected in lower concentrations of Pb in the forested soils than in the grassed sites. There was not a significant difference (alpha=0.05) between exchangeable Pb forms and organic bound Pb forms between grass and forested sites. In forest soils, as depth increases the amount of exchangeable Pb increases and organic bound Pb decreases. For all soils, most of the Pb is bound to the Mn/Fe oxide fraction of the soil.

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