Underground long wall coal mining has the potential to impact on surface aquatic environments via subsidence, cracking of underlying rock and increased connectivity between surface and ground water. This would result in reduced surface water, changes in water chemistry (water quality) as a result of water flowing over newly cracked rocks and these changes may ultimately affect biota living in surface streams.
Changes in macroinvertebrate, diatoms and water quality were investigated in streams which overlie long wall coal mining and thus potentially have subsidence. The study was conducted in headwater streams on the Woronora Plateau in eastern New South Wales, Australia where the geology is predominantly sandstone. Water depth and water chemistry, macroinvertebrate and diatom assemblages were analysed. Both reference and mined areas were chosen because they were otherwise relatively undisturbed. Trace metals were used as tracers of altered exchange between surface and ground waters as a result of subsidence. These metals are virtually absent from undisturbed streams but are released when groundwater flows through newly cracked sandstone of the study area. Li was detected in significantly higher concentrations at mined than reference sites. Sites downstream of mining also had significantly higher temperature and electrical conductivity, and concentrations of bicarbonate, barium, calcium, sodium, iron, and chloride. Edge and riffle macroinvertebrate assemblages at both mined and reference sites were dominated by chironomid dipterans. Significantly lower EPT (Ephemoptera, Plecoptera and Trichoptera) taxa richness (3.4 vs 5.5 and 2.4 vs 5.4, in edge and riffle habitat respectively), number of Trichoptera genus (7 vs 19 and 8 vs 22, in edge and riffle habitat respectively) was observed at mined sites relative to reference sites. Diatom communities also differed between mined and non-mined sites with significant reductions in abundance but a greater number of genus observed at mined sites.