A long history of heavy industry and urbanization in Cleveland (Ohio, USA) has created a legacy of degraded soils, characterized by heavy metal and organic contaminants. Combined with massive losses in population and industry, such cities are accumulating large amounts of vacant land, for which new uses are being sought, such as for recreational space and urban farming. However, the history of this and other post-industrial cities limits the capacity for soil services upon which all terrestrial ecosystems depend. The objective of this study was to determine the legacy effects of industrial urbanization compared to relatively undisturbed nearby Metropark soils and measure the possible reversal of these legacy effects by organic soil management in urban farms relative to rural organic farms with no industrial history.
Results/Conclusions
Soils of urban vacant lots were highly disturbed by human activity and showed significantly elevated levels of polycyclic aromatic hydrocarbons (PAHs), heterocyclic aromatic compounds (HACs), and heavy metals, including As, Ba, Cr, Fe, Ni, Pb, and Zn, compared to Metropark soils. Of greatest concern, Pb exceeded the Ohio EPA VAP screening level for residential soils (400 mg kg-1) in more than half of the vacant lots (VL). By comparison, urban farms (UF), comprising a spectrum of organic farming management applied to former VL soils, showed significant reductions in PAHs, HACs, and most heavy metals, particularly Pb, along with increases in organic matter and better moisture retention. Although contaminants in UF soils were still higher than those in rural farms and Metroparks, they also contained higher levels of many nutrients essential to plant growth than even rural farm soils. The parameter showing the strongest association with these improvements was soil organic matter, which was highly negatively correlated with Pb, Ba, and As in UF soils, but not in VL. These results suggest that inputs of composts and other active organic matter associated with organic agriculture can improve soil quality and fertility, providing multiple benefits for soil health and improved ecological services.