Source tracing of soil Cu and Pb based on spatial structure characteristics—A case study in the sewage irrigated area in the southeast suburb of Beijing

Objectives Regional pollution sources of soil heavy metals can be analyzed by their spatial structure characteristics. In this paper, spatial structure characteristics of pollutants Cu and Pb were studied in order to analyze causes of heavy metals in a sewage irrigation area in southeast suburb of Beijing.

Methods In this paper, southeast suburb of Beijing was selected as the study area. Firstly, points were uniformly set up in the whole area with 1 km × 1 km sampling density. Based on uniformed distribution points, sampling was carried out in the sewage irrigation area with the same sampling density (1 km × 1 km) and 376 soil samples were collected finally. At each sampling site, 5 sub-samples were taken from the 4 vertexes and the center of a square block (10 m × 10 m) and mixed thoroughly to select 1 kg soil as the representative sample of the site. Total soil Cu and Pb contents were determined using a flame atomic absorption spectrometer, their spatial structures were analyzed and distribution characteristics were described using Variowin 2.0 and ArcGIS 10.2 software in order to study their contamination causes.

Results The spatial structures of both Cu and Pb in the studied area were nested structures, and nugget/sill ratios were between 25% and 75%. The spatial distribution of Cu and Pb was closely related to the river flows, and their spatial correlation was strong in northwest–southeast direction. The high values of heavy metals were mainly distributed in the Liangshui River basin (located in the north central of the study area), Yongding River basin (located in the west of the study area) and northeast of Tongzhou District.

Conclusions The main sources of heavy metals were sewage irrigation and soil parent material. The spatial auto correlation distances of Cu and Pb dominated by small-scale factor such as sewage irrigation were 11.35 km and 9.49 km, respectively. However, the spatial auto correlation distances dominated by large-scale factor such as soil parent material were 26.65 km and 31.70 km, respectively. Through the analysis of different scale factors which have effects on spatial distribution of regional soil heavy metal contents, the sources of soil heavy metal pollution could be revealed. This idea can be provided as reference to study the sources of soil heavy metal pollution in other regions.