Since 1976, an estimated 7% of the Appalachian ecoregion has been converted into surface mines through mountaintop mining with valley fill (MTMVF) operations. The alkaline mine drainage (AlkMD) produced from these operations has been implicated in substantial declines in aquatic ecosystem biodiversity and secondary production and as a significant source of toxic levels of selenium (Se) to downstream waters. We asked whether these impacts of AlkMD contamination propagate beyond the boundaries of aquatic systems by examining whether the transfer of energy or selenium via emergent aquatic insects to terrestrial food webs is affected by AlkMD. We compared the mass of emerging aquatic insects along with the density, biomass and Se content of riparian spiders (Tetragnatha sp) between six mined and three unmined streams in West Virginia. Within the mined streams, we compared three streams that did and three that did not include settling ponds, habitats where we anticipated that selenite reduction would be favored, thus increasing the biological assimilation of Se.
Results/Conclusions
Our results indicate that the impacts of AlkMD contamination are affecting terrestrial food webs, both by reducing the transfer of energy and enhancing the transfer of Se. There was a 64% reduction in the average density of spiders caught along mined streams compared to unmined streams, indicating a reduction in the energy subsidy available to spiders through emergent insects. Se content in spiders along mined streams were significantly elevated (p=0.0374), with average Se concentration more than twice that of spiders caught along unmined streams. The presence of settling ponds also significantly elevated the spider Se content (p=0.0172), with the average Se content twice that of spiders along unponded, mined streams and five times that of spiders along unmined streams. These spider Se concentrations found at ponded, mined streams are among the highest values reported for spiders in the literature. This result speaks to the chronic nature of MTM as a source of contamination and demonstrates that ponds are ineffective in settling Se and may even promote its uptake into biota. All these results taken together emphasize the importance of insect emergence in propagating the impacts of AlkMD contamination and indicate that terrestrial organisms in MTM ecosystems may consequently be at risk.