Influences of stormwater concentration infiltration on the heavy metal contents of soil in rain gardens

Abstract

Abstract Many studies have been conducted on water volume reduction and pollutants purification of rain gardens. However, the pollutant variations in rain gardens are rarely explored. Seven soil sampling events were conducted from April 2017 to February 2019 to investigate the influences of stormwater concentration infiltration on soil heavy metals in two rain gardens. The results show that: (1) Cu, Zn, and Cd contents in rain garden soil are greater than those of the control soil. They vary with seasons and are trapped in the top layer of 0–30 cm; (2) Cu, Zn, and Pb exist as iron–manganese oxide combined form (S3), organic bound (S4) and residual forms (S5). However, Cd exists in exchangeable (S1) and carbonate bound (S2) forms, whereas Cr is in the S2, S3, and S4 forms. (3) According to the Soil Environmental Quality Standard in China, rain gardens, running for 8–9 years, are relatively clean and, within level II. However, compared with the background content of Shaanxi Province and the world, they are moderately or even heavily polluted by Cd and Zn and slightly polluted by Cu. It indicates that rain gardens have the risk of heavy metal pollution from stormwater concentration infiltration.