Recovery of bacterial community structure in a chronosequence of reclaimed coal mined soil under two vegetative regimes

Authors: Brooks, John; Adeli, Ardeshir; Smith, Renotta; MCGREW, REBECCA - North America Coal Cooperation; Read, John

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2019
Publication Date: 6/27/2019
Citation: Brooks, J.P., Adeli, A., Smith, R.K., McGrew, R., Read, J.J. 2019. Recovery of bacterial community structure in a chronosequence of reclaimed coal mined soil under two vegetative regimes. Journal of Environmental Quality. 48:1029-1037. https://doi.org/10.2134/jeq2018.09.0349.
DOI: https://doi.org/10.2134/jeq2018.09.0349

Interpretive Summary: Lignite (coal) mining operations can have deleterious effects on the soil physical and chemical makeup, but also on the soil biology. Coal mining operations remove much of the organic matter from the soil, basically leaving barren soil material that is not suitable for agriculture. Mine operations actively reclaim this soil material. One approach is to plant grass seed, fertilize, and then return the land to either pasture or wood lands. Most reclamation processes use either visual or measured parameters to determine the success of the reclamation process. One ignored parameter is soil biology, specifically the soil bacteria and fungi. This study followed a chronological sequence of reclamation in a regional mining operation in Mississippi. The study focused on uncultured bacteria by using DNA from soil bacteria to determine the effect that mining reclamation had on the bacterial community species richness, diversity, and structure. Pasture and wood reclaimed lands were sampled and consisted of reclamation periods from 1 to 13 years prior to sampling, with comparisons made to unmined soils located on the mine. The study determined that the mining reclamation process quickly established bacteria back into the reclaimed soil, despite soil physical properties which were less than ideal for agriculture. Over the 13 years of chronology, the bacterial population evolved and shifted to a less rich population, meaning there were less bacterial species at 13 years than at 1-year post reclamation. The soil bacterial populations were variable, as would be expected, but overall vegetation dominated the changes to the microbial populations with wooded reclaimed soils showing less diversity and richness than pasture, but still more than reference sites. Overall, this study demonstrated that mine reclamation using bermudagrass and/or wooded restoration can reestablish the microbial community to equal to or greater than previously defined.

Technical Abstract: Lignite (coal) mining operations can have deleterious effects on the soil physical and chemical makeup, but also on the below surface microbiological community. Effectively, the removal of nearly all organic matter from the upper layers of soil can reduce the effectiveness of any soil to support vegetative growth to simply preventing erosion. One of the primary effectors in these processes is the soil microbial community, and up until recently, microbial community parameters were not considered in the successful reclamation of mined soils. The current study proposes to measure the uncultivated bacterial community in a chronosequence of reclaimed lignite mine lands in Mississippi. A 16S rRNA targeted metagenomic study was undertaken on each of 30 sampling sites, utilizing the Mothur bioinformatics suite of analyses. The study sites comprised samplings of reclaimed field sites, both pasture and wooded, in triplicate consisting of 1 to 13 years post reclamation time. Comparisons were made to unmined wooded reference sites, located on the mine. Overall, the study determined that the primary driver of bacterial community dynamics was the vegetative cover. Chao (richness) estimations for operational taxonomic units (OTUs) showed recently reclaimed sites (~1 y) were more species rich with a level of ~3200 compared with reference site levels of <2500. Similarly pasture reclaimed sites were more species rich than reference and wooded sites. Variability within the reclaimed sites was expectedly high (homova), particularly early in the reclamation process, but it appeared to stabilize throughout the process as reclaimed site richness and diversity levels (invSimpson) decreased. This was most likely a result of the reclamation management shift from pasture to wooded lands. Additionally, principal components analysis of theta YC phylogenetic tree branch lengths indicated that vegetative and time-binned sites clustered together. Overall, this study demonstrated that mine reclamation using bermudagrass and/or wooded restoration can reestablish the microbial community to equal to or greater than previously defined. It is interesting to note that reference site communities were vastly different in community structure than reclaimed sites, indicating that communities don’t revert to baseline levels.