Soil samples were collected from the upstream, midstream and downstream areas of the Shuimo River in three layers of 0–20, 20–40 and 40–60 cm, and each group of sample points was located 5 m, 1 km and 2 km away from the river bank, respectively. The analysis was carried out. Based on the investigation and research, six indicators, including As, Pb, Zn, Cu, Ni and Cr, were designated as evaluation factors in combination with the results of the sample collection with low or no detectable values of Cd and Hg. The mean values of the samples measured in the upper, middle and downstream layers were taken, and the degree and source of pollution were evaluated and jointly analyzed using the gray correlation analysis and factor analysis methods. By using the gray correlation analysis, it was found that the evaluation results of the upstream and middle reaches of the soil along the Shuimo River were both level 3, with slight pollution, and the evaluation results of the downstream areas were level 2, with good soil quality. There are two main sources of pollution obtained through the factor analysis; source 1 is mainly heavy metals such as Zn, Cu, Cr, Pb and Ni, while source 2 is mainly heavy metals such as As, Pb and Ni. The amount of pollution sources is inferred from the heavy metal types of each source and the soil environment along the Shuimo River as industrial and human sources of pollution. From the analysis results, the combination of the gray correlation analysis model and factor analysis model is convenient and fast and can accurately quantify the source contribution of various pollution sources. Not only can it reflect the actual situation more objectively and realistically in the evaluation of soil heavy metal pollution and pollution sources, but also the calculation is simple and easily applied with low data requirements.

Heavy metal pollution in the surface sediments of urban rivers has a significant influence on the safety of city residents. This study explores the features of heavy metal pollution in the surface sediments of the Shuimo River and provides a theoretical basis for decision makers regarding river management and restoration. This study uses principal component analysis and kriging interpolation to analyse the pH values and pollution characteristics of nine heavy metals (As, Pb, Zn, Cu, Ni, Fe, Mn, Cr, and V) in 23 surface sediments of the Shuimo River. The results showed that the pH value of the surface sediments along the direction of water flow had a quadratic curve trend. Kriging interpolation revealed consistency in the spatial distribution of heavy metals and Fe, and the peak value was from Qidaowan to Weihuliang. There were significant positive correlations (p < 0.05) between Fe and Pb; Mn, Cr, V, Cu, and Zn; and Mn, Cr, and V. The principal component analysis showed that the main heavy metals in the surface sediments of the Shuimo River were Fe, Zn, Cu, and As. The total amount of heavy metals was in the order of Fe > Mn > Zn > V > Cr > Ni > Cu > Pb > As, ranging from 11.27~18,760.97 mg·kg⁻¹. The cluster analysis classified the nine heavy metals into four categories: Zn and Cu in the first category; Ni in the second; As and Pb in the third; and V, Cr, Mn, and Fe in the fourth.