Effects of anthropogenic particles on the chemical and geophysical properties of urban soils, Detroit, Michigan.

摘要

There is a great need in many cities for a better quality of urban soil maps. This is due to the increasing interest in repurposing vacant land for urban redevelopment, agriculture, and green infrastructure. Mapping vacant urban land in Detroit can be very difficult because anthropogenic soils were often highly variable and frequently contained demolition debris (such as brick), making it difficult to use a hand auger. This study was undertaken in Detroit, MI to create a more efficient way to map urban soils based on their geophysical and chemical properties. This will make the mapping process faster, less labor intensive, and therefore more cost effective.;Optical and chemical criteria for the identification and classification of microartifacts (MAs) were made from a set of reference artifacts of a known origin. These MAs were then observed and tested in urban topsoil samples from sites in Detroit, Michigan that represent three different land use types (residential demolition, fly ash-impacted, and industrial). Optical analyses, SEM, EDAX, and XRD showed that reference MAs may be classified into five basic compositional types (carbonaceous, calcareous, siliceous, ferruginous and miscellaneous). Reference MAs were generally distinguishable using optical microscopy by color, luster, fracture and microtexture. MAs that were more difficult to classify were further differentiable when using SEM, EDAX, and XRD.;MAs were found in all of the anthropogenic soils studied, but were highly variable. All three study sites had concentrations coal-related wastes were the most common types of MAs observed and often included coal, ash (microspheres, microagglomerate), cinders, and burnt shale. MAs derived from waste building materials such as brick, mortar, and glass, were typically found on residential demolition sites. Manufacturing waste MAs, which included iron-making slag and coked coal were commonly observed on industrial sites. Fly ash-impacted sites were composed of only microspheres and microagglomerate that were concentrated within the soils by airborne deposition, making it widespread. These results support the hypothesis that MA assemblages of distinct composition vary with land use. Therefore, it seems likely that magnetic susceptibility surveying and other geophysical methods will prove effective for mapping anthropogenic soils on vacant urban land.;Anthropogenic soils and MAs were assessed for pH, electrical conductivity (EC), and magnetic susceptibility (MS). The A horizons of urban soils at residential demolition, industrial-impacted, and fly ash-impacted sites were found to be distinguishable from those of native soils. Anthropogenic soils were higher by one pH unit or more than the background level, had an EC value two to three times the background level, and had MS measurements up to 20 times greater than the background level. The analysis of reference artifacts suggested that the elevated pH of anthropogenic soils was caused by calcareous building material wastes, the elevated EC were the result of both calcareous and ferruginous wastes, and elevated MS were attributable to ferromagnetic materials. Anthropogenic soils collected at residential demolition sites were differentiable by EC, whereas those at collected form industrial sites were distinguishable using MS. Therefore, anthropogenic soils and native soils have a unique chemical and geophysical signature which can be highly dependent on the concentration of MAs. This suggests that EC and MS surveying methods may be used to remotely sense and map urban soils more effectively than using traditional methods alone.