Biological impacts of acid mine drainage in the Dee River, downstream of the Mt Morgan Mine, Central Queensland, Australia

Mining for gold and copper was undertaken for nearly 100 years from 1882 at Mount Morgan in Central Queensland. Re -processing of. tailings ceased in the early 1990s and no mining has been conducted since. The legacy of the historical mining practices is an open cut (threatening to overflow) and acid mine drainage (AMD) extending for a considerable distance along the -Dee River. The first -18 km- of the river downstream- of- the mine, to its junction with Fletcher Creek, is severely impacted with pH consistently below 3.5. Water metal concentrations are many times higher than the water quality standards for freshwater biota. For example, the filtered mean concentrations of Al and Cu at 4 sites in this section of the river were 87.3 and 6.45 mg/L, respectively. Fish, molluscs and shrimp were absent and macroinvertebrate species richness was limited to only insects in this severely impacted region. Water quality of the river improves at the junction with Fletcher Creek and downstream the water quality is only severely impacted during periods of flow following rain events. This study examined the biological impacts downstream of the mine including the response of biota to flows in the river. Whilst previous studies had investigated spatial variations in macroinvertebrate communities this study also examined temporal variation and response to flow. The metal content of fish and mussels from the river were determined for the first time.