Coal is one of the world’s leading energy sources, accounting for 40% of worldwide electricity generation. While coal is a critical natural resource, its extraction represents a significant disturbance to surrounding stream ecosystems. Mountaintop mining and acid mine drainage have been shown to degrade physical, chemical, and biological characteristics of streams. However, we know little about the effects of mining-related surface subsidence. Surface subsidence is associated with longwall mining, a high efficiency extraction method that allows the roof of the mine to collapse following extraction. Subsidence fractures the rock within and beneath the stream bed and can thus impact stream flow. We investigated the effects of longwall mining and associated mitigation techniques on streams in southwestern Pennsylvania. We collected data from the Pennsylvania Department of Environment Protection. These data were submitted by environmental consultants on behalf of the mine operators in compliance with Pennsylvania mining regulations. Water chemistry parameters (pH, dissolved oxygen, and specific conductivity) and macroinvertebrate communities were sampled pre-mining, post-mining, and post-restoration. Macroinvertebrate community data was assessed using both multivariate statistics and a composite metric known as the Total Biological Score (TBS).
Results/Conclusions
We found that, on average, mining-related flow loss in streams reduces the aquatic macroinvertebrate TBS by nine points (ANOVA, mining effect, P < 0.0001). This reduction constitutes an adverse effect to the macroinvertebrate community under Pennsylvania regulations. Non-metric multidimensional scaling (NMDS) confirmed that community composition is significantly different following mining-induced flow loss (permutation test, mining effect, P = 0.001). Certain mayfly taxa – Ephemerella, Eurylophella, and Epeorus – exhibit large declines in frequency and appear to be particularly sensitive. These community changes may be driven in part by changes in stream chemistry, as specific conductivity nearly doubles following subsidence-related flow loss (pre-mining: 169.1μS +/- 9.1, post-mining: 329.9μS +/- 12.3; P < 0.0001). In the Western Allegheny plateau, conductivities above 300μS are outside the benchmark for aquatic life set by the US EPA. Subsidence-related stream pooling also reduces the macroinvertebrate TBS. However, gate cut mitigation techniques are successful in restoring pooled streams to their pre-mining condition. We recommend that future research in this area focus on 1) the relationship between elevated conductivity and macroinvertebrate communities after mining-induced flow loss and 2) the effectiveness of mitigation in restoring streams impacted by flow loss.