Objective The aim was to explore the content and spatial distribution characteristics of heavy metals in urban forest soil in Harbin, identifying the core pollution factors and key influencing pathways of heavy metals in the study area, and conducting ecological risk assessment of heavy metal pollution.

Methods In this study, soil samples from 112 randomly selected plots within the fourth ring road of Harbin were collected using a grid method, and the contents of Hg, Cu, Zn, and Pb were determined. The spatial distribution maps of soil heavy metals were drawn using ArcGIS. The multiscale geographically weighted regression (MGWR) was used to compare and analyze the correlations between various factors and the four heavy metals. The geo-accumulation index method and potential ecological risk index method were adopted to evaluate the heavy metal pollution in the study area.

Results The contents of the four heavy metals in the study area were 2.29, 1.43, 1.81, and 1.18 times the background values of Harbin soil, respectively. Among the soil physical and chemical properties, cation exchange capacity and total nitrogen were negatively correlated with soil heavy metals, while the others were positively correlated. Among the environmental characteristics of the plots, tree species diversity was positively correlated, tree density was negatively correlated, and urbanization intensity factors were all positively correlated. The average geo-accumulation index of Hg was 0.61, reaching a level of slight pollution. The potential ecological risk coefficients from largest to smallest were Hg > Cu > Zn > Pb, and the average total potential ecological risk index was 106.74, falling within the range of slight ecological risk.

Conclusion The average concentrations of the four heavy metals in this area were all higher than the soil background values in Harbin. Organic matter, tree density, and impervious surface ratio were the key influencing pathways of soil heavy metals. From the perspective of the accumulation index in the soil, the pollution levels of heavy metals Hg and Zn were classified as Grade 1. Analyzing from the potential ecological risk, the heavy metal pollution in the study area had reached the range of mild ecological hazard.