Hydrochemical characteristics and microbial community evolution of Pinglu River affected by regional abandoned coal mine drainage, Guizhou Province, China

Pinglu River in southwestern China was continuously polluted by acid mine drainage (AMD) from abandoned coal mines, and AMD has become a major source of recharge to the river (43.26% of total flow), resulting in structural changes in the physicochemical properties and microbial communities of river water and sediments. In this study, we collected abandoned coal mine drainage, river water, and river sediment samples for comprehensive analysis. Results indicated that the hydrochemical types of AMD from abandoned coal mines were mainly SO4-Ca center dot Mg. The pH of river water in Pinglu River decreased from upstream to downstream due to AMD, with the hydrochemical type gradually changing from SO4 center dot HCO3-Ca center dot Mg to SO4-Ca center dot Mg. The variation of pH along the river sediments was less than that of water samples, which remained weakly alkaline. However, high-throughput sequencing revealed a gradual decrease in microbial diversity in river sediments from upstream to downstream. The core bacteria groups in the upstream sediments were mainly attributed to the phylum Proteobacteria and Actinobacteriota, mainly including Geobacter, Anaeromyxobacter, Marmoricola, and Phycicoccus. The relative abundance of Gaiella, MND1, and Pseudolabrys in sediment samples gradually increased with the confluence of AMD, and the differences in microbial communities may be attributed to pH, TOC, and TP. Results of phenotype prediction demonstrated that the relative abundance of anaerobic microorganisms in river sediment gradually decreased from upstream to downstream (from 24.77 to 12.46%), presumably due to the large amount of oligotrophic AMD converge.