Effects of surface coal mine drainage on stream microbial communities

Background/Question/Methods

Surface coal mining is the dominant form of land cover change in northern and central Appalachia. Central Appalachian watersheds that contain surface coal mines are associated with streamwater chemistry that is elevated in conductivity, alkalinity, and pH and may also be enriched with trace metals and metalloids such as Al, Mn, and Se. In this study, we examined the cumulative impact of surface mining on streamwater chemistry and stream microbial community composition in the Mud River upstream, within, and downstream of the Hobet Mine complex, the largest single surface coal mine operation in the central Appalachians. We expected to find that streamwater upstream of the mine would have lower conductivity, sulfate, and metal/metalloid concentrations compared with sites throughout and downstream of the mine. We also anticipated finding significant differences between the upstream and within/downstream microbial community compositions.

Results/Conclusions

Upstream of the mine, surface water chemistry had low conductivity (156.1 μS, S.E. 11.6), sulfate (32.5 μS, S.E. 4.5) and low metal/metalloid concentrations while the most downstream sampling site within the mine complex had 1525 μS (S.E 126.9) conductivity, 194.5 mg/L (S.E. 73.5) sulfate and higher concentrations of a suite of metals and metalloids. Selenium concentrations ranged from 10.2 to 19.0 μg/L at the most downstream site. Unexpectedly, nitrate concentrations increased dramatically through the mining complex, with several valley fill outflows having TN concentrations >15mg/L. Nitrate was highly correlated with selenium concentration, both of which were highest in outflows from recently permitted surface mines within the complex. Microbial biomass, measured by substrate induced respiration, was higher within the mining impacted stream segments than in upstream reference reaches. Microbial community composition shifted dramatically along the river network (NMS Ordination R² = 0.88), with the communities upstream of mining distinctly different from those below tributaries draining surface mines. Within the 12km mining impacted stream network, we observed differences between communities in tributaries draining actively mined watersheds vs. tributaries draining reclaimed mines.