Trace metals interaction to soil properties, and their ecological risk assessment in different disturbance regimes of sal forests of the western Himalaya, India

Disturbance is an important factor in controlling vegetation diversity, and distribution of trace metals in the environment, including through their mobilization by disturbance-induced runoff and related to movement of soil particles. Disturbance-induced access of these trace metals into the ecosystem is toxic for soil contamination and experiences varying degrees of ecological implications in different ecosystems. The present study aimed to evaluate the impact of different degrees of land disturbances on the changes in vegetation diversity, soil characteristics, and trace metals in the Himalayan forest ecosystem, which is limitedly documented. Forest sites were categorized into four distinct disturbance classes based on disturbance index score (DI): no disturbance (ND, DI ≤ 5 %), low disturbance (LD, 5 < DI ≤ 20 %), moderate disturbance (MD, 20 < DI ≤ 50 %), and high disturbance (HD, DI > 50 %). Data comprised trace metals, and soil physicochemical characteristics across the distinct disturbance classes and soil layers (0-15 and 15-30 cm). Using two-way ANOVA, vegetation attributes (diversity (H′), and tree density), soil properties, and trace metals were tested for their effects, including interactions among different disturbances and depths. Multivariate correlation was used to investigate the relationship between disturbance classes, depths, soil characteristics, and trace metals. The important findings of the study are the following: (1) The recruitment of new trees (Tree_recru.), diversity, and soil organic carbon (C_org) were significantly varied across the disturbance classes (p< 0.05) and followed the order: MD > HD > LD > ND; (2) Average concentration metals were significantly distributed along disturbances gradient HD > LD > MD > ND in the order: B > Mn > Pb > Cu > Ni in distinct soil layer. (3) Contamination factor of trace metals in order B > Mn > Pb > Ni > Co > Cu in 0-15 and 15-30 cm soil depths. (4) Persistent ecological risk index (PERI) was higher for HD sites and lowest for ND sites. The result illustrated that moderate disturbance increases diversity and soil nutrients. The study highlighted the important role of disturbance in regulating the trace elements in association with changes above-below ground interaction, suggesting HD sites as a potential source of environmental contamination.