Spatial distribution of soil trace element concentrations along an urban-rural transition zone in the black soil region of northeastern China

Purpose Urbanization is an important process that changes land use pattern and the sustainability of agroecosystems in the urban-rural transition zone. Through intensified anthropogenic activity, urbanization magnifies trace element (TE) inputs into soils and alters the balance of soil element fluxes. This study aims to investigate the effects of urbanization on the spatial dynamics of soil HMs in peri-urban zones and the distinct behaviors of TEs in response to urban sprawl. Materials and methods An area (15 km × 16 km) in the Chinese northeastern black soil region was selected to represent a typical urban-rural transition feature that received heavy impact by urbanization in last decade. Two hundred topsoil samples were taken from locations dominated by Phaeozem soils and analyzed for total Zn, Cu, As, Pb, Cd, Cr, Ni, and Hg. Principal component analysis (PCA) was used to distinguish the probable sources of TE inputs into the soils. The overall TE pollution of soils was evaluated by the Nemerow comprehensive pollution index. Inverse distance weighting algorithm combined with autocorrelation analysis was used to analyze the spatial patterns of soil TE distribution. Results and discussion The mean concentrations of the studied TEs, with the exception of Hg and As, were higher than their background values, and their concentrations were always higher in the part closer to the urbanized area. Soil pollution assessment shows that the overall pollution status was moderate, but for Cd and Cu, numerous hotspots were identified due to the overuse of agrochemicals. PCA showed that Cu, Zn, Pb, and Cd as the first component were due to urbanization and agronomic practices, whereas As, Ni, and Cr as a second group were primarily of lithogenic origin, partly due to urbanization, and Hg was related to the atmospheric deposition of industrial waste gas. Conclusions Increasing urban sprawl in the study area resulted in higher TE concentrations in the southern part of the region than the northern part, confirming the positive effect of urbanization on excessive soil TE accumulation. Although the pollution status was not yet serious, with the current rate of urban growth, arable soils in the peri-urban area will continuously be contaminated and control measures must be taken to prevent the cumulative impact on human health.