An integrative assessment of a watershed impacted by abandoned mined land discharges.

The Ely Creek watershed in Lee County, VA, USA, contains an abundance of abandoned mined land areas with acid mine drainage (AMD) that contaminate the majority of the creek and its confluence into Stone Creek. Acidic pH measurements ranged from 2.73 to 5.2 at several stations throughout the watershed. Sediments had high concentrations of iron (approximately 10,000 mg kg-1), aluminum (approximately 1,500 mg kg-1), magnesium (approximately 400 mg kg-1) and manganese (approximately 150 mg kg-1), and habitat was partially to non-supporting at half of the stations due to sedimentation. Benthic macroinvertebrate surveys at six of 20 stations sampled in the watershed yielded no macroinvertebrates, while eight others had total abundances of only one to nine organisms. Four reference stations contained > or = 100 organisms and at least 13 different taxa. Asian clam in situ toxicity testing supported field survey results. Laboratory, 10-day survival/impairment sediments tests with Daphnia magna and Chironomus tentans and 48-h water column bioassays with Ceriodaphnia dubia indicated environmental stress to a lesser degree. Ten parameters that were directly influenced by AMD through physical, chemical, ecological and toxicological endpoints were assimilated into an ecotoxicological rating (ETR) to form a score of 0-100 points for the 20 sampling stations, and the lower the score the greater the AMD stress. Twelve of the 15 sampling stations influenced by AMD received an ETR score of 13.75-57.5, which were categorized as severely stressed (i.e. comprised the < 60 percentile category) and worthy of the highest priority for future ecological restoration activities in the watershed.

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 (FeS(2)) is oxidized on exposure to oxygen and water to form ferric hydroxides and sulfuric acid. If produced in sufficient quantity, iron precipitate, heavy metals (depending on soil mineralogy), and sulfuric acid may contaminate surface and ground water. 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 correlated 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 factors were the best indicators of toxicity in this system. Nine sampling stations were selected based on proximity to major AMD inputs in the watershed. In 48-h exposures, sediment samples from three stations were acutely toxic to D. magna, causing 64-100% mortality, whereas water samples from five stations 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 samples. 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 fact that toxic sediments had high percent water content, water chemistry appears to be a more important adverse influence in this system than sediment chemistry.