Abstract
Natural wetlands are known to play an important role in pollutant remediation, such as remediating acid mine drainage (AMD) from abandoned mine sites. However, many aspects of the microbiological mechanisms underlying AMD remediation within wetlands are poorly understood, including the role and composition of associated microbial communities. We have utilized an AMD-polluted river-wetland system to perform rRNA sequence analysis of microbial communities that play a role in biogeochemical activities that are linked to water quality improvement. Next-generation sequencing of bacterial 16S rRNA gene amplicons from river and wetland sediment samples identified variation in bacterial community structure and diversity on the basis of dissolved and particulate metal concentrations, sediment metal concentrations and other water chemistry parameters (pH and conductivity), and wetland plant presence. Metabolic reconstruction analysis allowed prediction of relative abundance of microbial metabolic pathways and revealed differences between samples that cluster on the basis of the severity of AMD pollution. Global metabolic activity was predicted to be significantly higher in unpolluted and wetland sediments in contrast to polluted river sediments, indicating a metabolic stress response to AMD pollution. This is one of the first studies to explore microbial community structure dynamics within a natural wetland exposed to AMD and our findings indicate that wetland ecosystems play critical roles in maintaining diversity and metabolic structure of sediment microbial communities subject to high levels of acidity and metal pollution. Moreover, these microbial communities are predicted to be important for the remediation action of the wetland.
Highlights
Pollution from abandoned mine sites is a major environmental problem that has deleterious consequences for aquatic and terrestrial ecosystems (Bridge, 2004)
The southern and northern Afon Goch rivers are both exposed to acid mine drainage (AMD) but have very different environmental characteristics, due in part to the presence of the natural wetland on the southern river, which is dominated by Juncus sp. and some E. angustifolium and Phragmites sp
There was a large dominance of taxa incorrectly classified by the Greengenes database as “Cyanobacteria,” but which include eukaryotic Stramenopiles that were identified via a chloroplast sequence, and so will slightly inflate the bacterial species richness values. This is probably due to the presence of diatom species, which we have previously identified from this wetland by 16S rRNA gene amplicon sequencing (Dean et al, 2013)
Summary
Pollution from abandoned mine sites is a major environmental problem that has deleterious consequences for aquatic and terrestrial ecosystems (Bridge, 2004). For many mines, including coal mines, the drainage is highly acidic This acid mine drainage (AMD) is generated when metal sulfide minerals, mainly pyrite, are oxidized in the presence of water and accelerated by the action of chemolithotrophic bacteria. This generates acidity and mobilizes large concentrations of iron (Fe), and other toxic trace metals and metalloids, depending on the composition of the exposed rock (Robb, 1994; Mason, 2002). AMD pollution from abandoned mines worldwide is a major problem that needs to be mitigated and managed (Hedin et al, 1994; Mayes et al, 2009b)
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