[Spatial Diffusion Mechanism Underlying Peri-urban Cropland Heavy Metal Contamination in the Black Soil Region]

The spatial diffusion mechanism underlying cropland heavy metal contamination in a complex peri-urban environment provides a crucial basis for controlling soil contamination from the source and also for ensuring the quality of black soil croplands. However, previous studies have struggled to locate the contamination sources or trace their diffusion trajectories in space. In this regard, representative peri-urban croplands in the black soil region were selected as a case, and soil As, Pb, Hg, and Cd were deemed as the main research objects. Moreover, an affinity propagation algorithm and spatial autocorrelation regression were adopted to measure the contamination patterns and identify the major determinants, in an attempt to reveal how heavy metals are diffused in the peri-urban cultivated area. The results indicated that ① the average concentrations of soil As and Cd were 39.35 mg·kg^-1 and 0.183 mg·kg^-1, respectively, which exhibited heavier accumulation in the study area. The Nemerow index indicated that there were 52.38% of croplands indicating slight contamination. ② The affinity propagation algorithm identified three potential sources with a similar impact extent for As, which were situated in the typical cultivated area. Both of the two identified potential sources for Pb were situated in close proximity to Fanjiatun Town. The diffusion patterns for Hg and Cd were complex, particularly for the latter, of which the potential sources were scattered in multiple places. ③ The spatial lag model indicated that the distributions of As and Cd were mainly controlled by the intensive agriculture in peri-urban areas, among which As was related to the application of herbicide and Cd was related to the distribution of protected agriculture. Pb was mainly influenced by urbanization and industrialization, whereas Hg was found to be associated with the migration conditions of the soil. However, the regulating function provided by either croplands or their nearby environment did not play an important role in determining the diffusion patterns of heavy metals. The present study enriches the theory and methods for the spatial analysis of cropland heavy metal contamination and is significant for controlling contamination from the source in peri-urban croplands in the black soil region.