Effects of heavy metal pollution on soil physicochemical properties and microbial diversity over different reclamation years in a copper tailings dam

Abstract

The proliferation of copper (Cu) mines has led to a rapid rise of tailings dams comprised of mining metal mineral material, causing serious damage to the ecological environment of mining areas. Soil physicochemical characteristics, enzyme activities, and microbial diversity are important indices for ecosystem functions as well as being important factors in evaluating soil restoration characteristics. This study selected nine Cu tailings subdams in Yuanqu County, Yuncheng City, Shanxi, China, to analyze the effects of heavy metal pollution on soil physicochemical properties and microbial diversity over different years of reclamation. We found that these different years of reclamation exhibited significant differences in physicochemical properties, and as restoration progressed, soil nutrient concentrations (i.e., carbon [C] and nitrogen [N]) significantly increased. Furthermore, we found significant negative correlations between catalase and the soil C and N ratio (C/N). In addition, urease was significantly positively correlated to N, C, and cadmium (Cd) as well as bacterial gene copies but was negatively correlated to zinc (Zn). Sucrase, on the other hand, was negatively correlated to Cd and bacterial gene copies. Over subsequent years of reclamation, we found that environmental factors affected bacteria more than fungi. Soil fungi diversity gradually increased as restoration progressed over consecutive years, while soil bacteria correspondingly exhibited an irregular trend. Results from this study could provide an ecological basis for further studies on soil ecosystem restoration and degradation mechanisms associated with Cu tailings dams.