Minor differences in sand physicochemistry lead to major differences in bacterial community structure and function after exposure to synthetic acid mine drainage

The formation of environmentally toxic acidic waste from mining activities is a world-wide problem. Neutralization of this waste can be accomplished by physicochemical and/or biological means. In this short-term study, synthetic acid mine drainage was added to sand-filled mesocosms containing silica-dominated (quartz) sand. Glucose was added as a carbon source for microbial iron and/or sulphate reduction. Replicates contained two separate batches of sand obtained from the same quarry site. The investigations used to assess and compare the chemical and biological functioning of the replicates included system hydraulic conductivity measurements, sand chemistry, effluent chemistry and bacterial community fingerprinting. Minor differences in composition of the sand, including the levels of available nutrients and micronutrients, resulted in major differences in measured parameters. Significant differences in effluent chemistry were found in systems containing different batches of sand. It was demonstrated that the characteristics of the sand and the presence of acid mine drainage (AMD) impacted the bacterial community structure and function. The importance of the physical substrate on the selection of functional microbial communities in systems remediating AMD should not be under-estimated. The physical substrate should be carefully selected and it may be prudent to include small-scale comparative studies in each particular setting prior to full-scale implementation.