An Investigation of Acid Rock Drainage in Glacial Streams Through Multivariate Exploratory Analysis and the Biotic Ligand Model in the Cordillera Blanca, Peru.

Water chemistry in the Cordillera Blanca, Peru, where glaciers provide crucial freshwater to the arid Andes Mountains, was characterized during the dry season (June-August), 2014. Metal concentrations, anion concentrations, and physical and chemical parameters were assessed at 94 sample sites in seven river valleys. Nonparametric multivariate exploratory statistics were used to compare sample sites. Compared to other river valleys, high metal concentrations were evident in the Quilcayhuanca valley. Water chemistry and visual signs indicated that acid rock drainage (ARD) is occurring in the Cordillera Blanca, likely due to glacial recession. Hierarchical clustering analysis was performed on the results of a principal components analysis on the chemical data. The results of these two analyses showed cobalt, manganese, and nickel were the top metals that distinguished the different clusters. In addition to the exploratory analysis, the Biotic Ligand Model (BLM) was used to predict toxicity to aquatic life based on the chemical measurements at the sampling sites. Approximately 20% of the sites had predicted toxic responses to metals and another 20% of the sites were outside of the pH tolerance range of individual species. These sites outside of the pH ranges were assumed to cause toxicity to the aquatic organisms due to hydrogen ions rather than metals. From this, the altered water quality in headwater streams in the Cordillera Blanca is predicted to be detrimental to aquatic life. The reduction in water quality makes the understanding of these headwater streams critical in efforts to mitigate the loss of crucial water resources