Zhongke Bai

Characteristics of labile organic carbon fractions in reclaimed mine soils: Evidence from three reclaimed forests in the Pingshuo opencast coal mine, China

The reclamation of discarded spoils has the potential to stimulate carbon (C) sequestration in reclaimed mine soils (RMSs). Nevertheless, to date the temporal dynamics of labile organic C fractions have not been sufficiently elucidated in RMSs. In this study, soil organic carbon (SOC) and labile organic C fractions, including microbial biomass organic C (MBC), easily oxidizable organic C (EOC) and dissolved organic C (DOC), were determined in Robinia pseudoacacia monoculture forests (reclamation periods of 0, 8, 10, 13, 15, 18 and 30years), Pinus tabuliformis forests (reclamation periods of 0, 10, 19, 23 and 25years) and Ulmus pumila forests (reclamation periods of 0, 18, 20 and 22years) situated on RMSs in the Pingshuo opencast coal mine, China. Changes in labile organic C fractions within the soil profiles (0-100cm) were also identified at the 18- or 19-year plots under the three monoculture forests. Our results showed that, SOC and labile organic C fractions, together with soil microbial quotient (SMQ) and C management index (CMI), increased with time since reclamation, indicating that the quality of RMSs improved over time after initial reclamation under the three forest types. R. pseudoacacia significantly increased the accretion of SOC and EOC in the early stage of reclamation while P. tabuliformis accelerated the accumulation of the MBC fraction. Results for U. pumila indicated that this species had a better ability to store C in RMSs 10years or more after reclamation. SOC and labile organic C fractions both had S-shaped distributions within the soil profiles (0-100cm), with the 0-20cm layer recording the highest values (P<0.05). Labile organic C fractions were closely associated and correlated with soil physicochemical properties; our results also showed that nitrogen played an important role in the development of labile organic C fractions. Overall, reclamation accelerated the accretion of both SOC and labile organic C fractions, results of which varied among the reclaimed forests.

Polycyclic aromatic hydrocarbons in the soil profiles (0–100 cm) from the industrial district of a large open-pit coal mine, China

Mining and industrial activities are the primary sources of soil pollution in the open-pit coal mine. The concentrations of PAHs in 11 sampling sites in the industrial district and 9 sampling sites with different land use types in Pingshuo open-pit coal mine, China, were measured to investigate the distributions of PAHs and possible sources in soil profiles (0–100 cm). In the topsoil layer (0–20 cm), concentrations of 16 PAHs ranged from 2.15 to 33.51 mg kg−1, with a mean value of 11.93 mg kg−1. PAHs were more variable in the middle soil layer (20–50 cm), ranging from 0.199 to 36.888 mg kg−1 with the average value of 9.21 mg kg−1. Comparable extreme concentrations were detected from the samples in the subsoil layer (50–100 cm). Compared with those in topsoil, the average concentrations of the most individual PAH species were less in the middle soil and subsoil layers. The concentrations of most of the individual PAHs in the topsoil were higher than those in the middle soil and subsoil. Distribution patterns of PAHs in the three soil layers correlated well with each other. The high concentration hotspots were concentrated around the old coal washery, reaching about 30 mg kg−1. The average concentrations of PAHs with different rings in the industrial district exceeded those in the other land use types. However, only the concentrations of 5-ring PAHs in topsoil showed difference with different land use types (P < 0.05). Diagnostic ratios and the total index showed that petroleum combustion was the main source of PAHs.

Evaluating relationships between soil chemical properties and vegetation cover at different slope aspects in a reclaimed dump

Conducting research about the relationships between soil chemical properties and vegetation coverage at different slope aspects is especially important in reconstructed ecosystems of vulnerable ecological regions. This study was conducted in the first reclaimed dump within the Pingshuo mining area of Shanxi Province, China, to analyze patterns of soil chemical properties (soil organic matter (SOM), soil total nitrogen (STN), soil available phosphorus (SAP) and soil available potassium (SAp) and vegetation coverage (NDVI) and their correlations at different slope aspects. In the reclaimed dump, 26 quadrats were established along four slope aspects (i.e., shady, semi-shady, sunny and semi-sunny slopes). There was no significant difference in SOM or STN among different slope aspects, while SAP differed between shady slopes compared to semi-shady, sunny and semi-sunny slopes; SAP differed significantly between semi-shady and semi-sunny slopes. The NDVI of semi-sunny slopes differed significantly from that of the other three aspects. There was variation in the relationships between NDVI and soil chemical properties, depending on the slope aspects. The logarithm of SOM and NDVI was related linearly on shady and semi-shady slopes, while NDVI was inversely related to the natural logarithm of the logarithm of SOM on sunny and semi-sunny slopes. STN and NDVI had a first-order function relationship on shady and semi-shady slopes, yet a quadratic function relationship on sunny and semi-sunny slopes. The relationships between SAP and NDVI were inverse on all types of slopes. On shady and semi-shady slopes, NDVI had a quadratic relationship with the logarithm of SAp, but it was well fitted by using a cubic function on sunny and semi-sunny slopes. The sensitivity coefficients of soil chemical properties and NDVI were different, and soil chemical properties changed differently depending on changes in NDVI at different slope aspects.