Effects of Pb, Cd, Zn, and Cu on soil enzyme activity and soil properties related to agricultural land-use practices in karst area contaminated by Pb-Zn tailings

Abstract

In order to study the impact of Pb, Cd, Zn, and Cu released by Pb-Zn tailings on soil enzymes and soil properties involving soil carbon and nitrogen cycle processes, 32 soil samples were collected from 2 different types of agricultural fields (one for growing corn and one for growing rice) contaminated by Pb-Zn tailings close to Sidi village in southwestern China. The results revealed that the paddy fields were seriously contaminated by Pb-Zn tailings compared with cornfields. Under the Pb-Zn tailings contamination, the population of fungi and actinomycetes as well as the activities of the soil enzymes (urease, invertase, and cellulase) in cornfields were significantly higher than those in the paddy fields. In addition, the results from path analysis showed that urease, invertase, and acid phosphatase were negatively correlated with DTPA-extractable Cd, Pb, and Zn (the direct path coefficients were-0.336,-0.314, and-0.591, respectively). Soil microorganisms and enzyme activities involving soil organic carbon and nitrogen decomposition and stabilization were decreased due to the toxic Pb-Zn tailings. Therefore, soil organic carbon and total nitrogen accumulate and an “elusive” carbon and nitrogen pool forms in the paddy fields compared with cornfields in the Pb-Zn tailings-contaminated karst area.