Heavy metal pollution assessment and soil property evolution under a natural ecological restoration process in a manganese wasteland in China

Abstract

The space‐for‐time method was used to track changes in heavy metals (HMs), selected physicochemical properties and soil enzyme activities at different restoration ages, that is 5, 10, and 25 years (named R5, R10, and R25, respectively) and in a natural forest (NF, age > 100 years, as the control) in the Daxin manganese (Mn) wastelands in China. The results showed that the HM concentrations decreased over time, with Mn exhibiting the highest concentration, followed by zinc, copper, and cadmium; all the studied sites exhibited heavy pollution levels based on the Nemerow multifactor index, with a very high potential ecological risk (RI) level in R5, moderate RI in R10 and R25, and low RI in NF; generally speaking, the soil physicochemical properties improved, with the exceptions of the available phosphorus (AP) and calcium (Ca) levels; the soil enzymes generally exhibited the highest activities in R25, while the activity of catalase showed a significant (p < 0.05) decrease over time; both the HM concentrations and physicochemical properties showed significant correlations with soil enzyme activities; redundancy analysis showed that soil pH and HM species should be given more attention in R5 for vegetation recovery; and the HM concentrations, soil moisture content, and ammonium nitrogen, total nitrogen, potassium, and magnesium levels might be the limiting factors for plant colonization in early restoration periods, while the AP, total phosphorus, and Ca levels might be the limiting factors in later restoration periods. The obtained results will provide guidance for the restoration of abandoned Mn‐polluted areas.