Spectroscopy application for soil differentiation in urban landscape

Abstract

The definition of urban soil is descriptive, a description of a state, not a taxonomic classification. There are no physical or chemical property lists for it as for general soils’ definition. “Urban soil” is a generic term and can be interpreted in many ways, but it refers to soils affected by urbanization. Urban soils supply environmental services and support the urban vegetation communities, despite being essentially different from natural soils. The main goals of this paper were to characterize urban soils in open green undisturbed patches and find a feature that will identify urban soils, not directly affected by urbanization process, like construction, residential, and transportation development. Seventy soil samples were collected from Mount Carmel National Park, city of Haifa’s remnant patches and disturbed sites. The samples were taken from horizon A, after the coarse organic particles or trash residues were removed. Two non-distractive spectral methods across visible and near, shortwave, and mid-infrared (VNIR-SWIR-MIR) spectral regions were used to characterize the soil minerology and total carbon content (0.35–25 μm) and analyzed by previously published top-down spectral unmixing method. The urban soils from all the city sites were found to be a combination of anthropogenic residue, contaminants alien like actinolite and chrysotile traces, local clay, and silicate minerals, while the park’s soils contained none. Furthermore, the average total carbon content found in urban soils was significantly lower than the amount found in the park’s samples. The results of the spectroscopy and analytical chemical analysis could not set apart the urban soils; all samples contained materials from anthropogenic origin. Yet, urban soil samples and park soil samples had different spectra features, which set the two soils significantly apart. The spectra of urban soil samples contain high absorption features at the VNIR and very few and much less information at the MIR wavelength. This fundamental difference can define urban-affected soils. The spectral feature found in this study may be useful for creating a non-destructive method to trace the urbanization changes in rapid acquisition of soil information at quantitative and qualitative levels.