Relative acute toxicity of acid mine drainage water column and sediments to Daphnia magna in the Puckett's Creek watershed, Virginia, USA

Acid mine drainage (AMD) is produced when pyrite (FeS2) is oxidized on expo sure to oxygen and water to form ferric hydroxides and sulfuric acid. If pr oduced in sufficient quantity, iron precipitate, heavy metals (depending on soil mineralogy), and sulfuric acid may contaminate surface and ground wat er. A previous study of an AMD impacted watershed (Puckett's Creek, Powell River drainage, southwestern Virginia, USA) conducted by these researchers indicated that both water column and sediment toxicity were significantly c orrelated with benthic macroinvertebrate community impacts. Sites that had toxic water or sediment samples had significantly reduced macroinvertebrate taxon richness. The present study was designed to investigate the relative acute toxicity of acid mine drainage (AMD) water column and sediments to a single test organism (Daphnia,magna) and to determine which abiotic factor s were the best indicators of toxicity in this system. Nine sampling statio ns were selected based on proximity to major AMD inputs in the watershed. I n 48-h exposures, sediment samples from three stations were acutely toxic t o D. magna, causing 64-100% mortality, whereas water samples from five stat ions caused 100% mortality of test organisms. Forty-eight-hour LC50 values ranged from 35 to 63% for sediment samples and 27 to 69% for water column s amples. Sediment iron concentration and several water chemistry parameters were the best predictors of sediment toxicity, and water column pH was the best predictor of water toxicity. Based on these correlations and on the fa ct that toxic sediments had high percent water content, water chemistry app ears to be a more important adverse influence in this system than sediment chemistry.