Impacts of point-source Net Alkaline Mine Drainage (NAMD) on stream macroinvertebrate communities

Over 4000 km of Pennsylvania's flowing waters and attendant ecosystems have been degraded by mine drainage to the exclusion of multiple designated uses. Both Acid Mine Drainage (AMD) and Net Alkaline Mine Drainage (NAMD) may result from coal extraction depending on the underlying geology. Acid Mine Drainage is characterized as an acidic mixture of toxic heavy metals in solution, while NAMD is circumneutral in pH with metals forming oxidized precipitates. The ecological impacts of AMD have been well documented but NAMD-impacted streams have received considerably less attention. We selected 10 low-order tributaries of the Ohio and Youghiogheny rivers in southwestern Pennsylvania impacted by point-source inputs of NAMD for assessment of water quality and benthic macroinvertebrate communities. Levels of pH, total iron (Fe), and sulfate (SO₄) were significantly elevated in the impacted stream reaches when compared with upstream reference sites while total alkalinity and specific conductance were equivalent. Macroinvertebrate abundance declined by 92% in the impacted stream reaches, but community structure in terms of taxonomic composition and species richness was similar. Total iron, total sulfate, and specific conductance were significantly linked to macroinvertebrate community impairment. The presence of resident macroinvertebrate communities in the unimpacted reaches suggests that remediation would result in a rapid recolonization and establishment of viable downstream ecosystems.