Reclaiming hard rock mine tailings and waste rock with pulp and paper sludge: a growth-chamber mesocosm study to investigate plant, chemical, and microbial community responses

A growth chamber trial was conducted to investigate the effects of two types of paper mill sludge on soil properties, microbial communities and germination rate and biomass production of annual ryegrass (Lolium multiflorum) in five different mine tailings. The organic amendments effectively improved the nutritional status of all the tailings substrates, examined in this study, and increased pH in acidic-generating tailings leading to significantly higher rate of germination and plant growth in sludge amended soils compared to control treatments (pure tailings substrates). The performance of each sludge type in each substrate seemed to be dependent on physiochemical properties of the sludge type as well as the mine tailings. The effects of sludge application on bioavailability of metals were very variable, and in some alkaline and acid-generating substrates the concentration of soluble Cu and Ni increased following organic amendments. Paper mill sludge additions also modified the microbial communities of the mine tailings. While mine tailings, in general, do not accommodate heterotrophic bacteria due to their oligotrophic nature, in the sludge amended substrates majority of DNA sequences were found to be closely related to heterotrophic bacterial species.