The origin and distribution of trace metals in the Rio Santa Watershed, Peru Elizabeth A. Walsh Department of Earth and Planetary Sciences McGill University, Montreal, Quebec, Canada April, 2013 A thesis submitted to McGill University in partial fulfillment of the requirements of the degree of Master of Science © Elizabeth Walsh 2013 Abstract The world’s highest density of tropical glaciers is found in the Cordillera Blanca of the Peruvian Andes. During the dry season, glacial meltwater is a vital fresh water resource in the region as it supplies up to 40% of river discharge. Climate change is driving rapid glacial retreat, causing serious concerns about future availability and quality of fresh water supplies. The purpose of this thesis is to survey water quality in the Rio Santa Watershed (which drains the western side of the Cordillera Blanca), with a particular focus on potentially toxic trace metals released by acid mine drainage and acid rock drainage. In July 2011, major ion samples were collected from 23 sites in the Rio Santa and nine of its tributaries. Samples for trace metal analysis were collected from 11 Rio Santa sites and eight tributaries. pH, temperature, and dissolved oxygen were measured in situ at all sites. Rio Santa discharge was measured directly at 15 locations and calculated by mass balance analysis for another 12 locations. Water in the Rio Santa Watershed is characterized by high concentrations of SO4, Ca, and HCO3. These species are derived from sulfide oxidation (both naturally occurring and enhanced by mining) and carbonate dissolution. The pH is circumneutral at all sites except for two tributaries, Rio Olleros and Rio Quilcay, which both had a pH below 5. Fe-oxyhydroxide coatings cover the streambeds of acid tributaries and some sites along the Rio Santa. As, Cd, Pb, Cu, Mo, Ni, and U concentrations tend to fluctuate above the detection level but below 10 ug/L at most sites in the watershed. Locally elevated concentrations occurred in the acidified Rio Olleros (70 ug/L of Ni) and Rio Quilcay (82 ug/L, 27 ug/L, 34 ug/L and 14 ug/L of Pb, Cd, Ni, and U, respectively.) Elevated concentrations also occurred in circumneutral tributaries Rio Tabla (43 ug/L of Ni) and Rio Llullan (720 ug/L of Mo and 180 ug/L of U.) In the Rio Santa, elevated trace metal concentrations occurred downstream of Ticapampa mine tailings pile (30 ug/L of As) and the city of Huaraz (73 ug/L, 58 ug/L, 53 ug/L, 40 ug/L, and 23 ug/L of Pb, Cd, U, Mo, and Ni, respectively.) Bulk loads of these indicator trace metals were near zero at the headwaters of the Rio Santa, and tended to increase steadily along the river’s length in proportion to increasing discharge, with large spikes in loads at Ticapampa and Huaraz. The dramatic decline in loads immediately after these sites is indicative of the non-conservative behavior of dissolved trace elements in the Eh-pH conditions of the Rio Santa. As dry season discharge continues to decline due to glacier recession, current contamination problems may be exacerbated and lower flows will inhibit the capacity of the watershed to buffer against acidic tributary and mining effluent inputs. ii Resume La plus grande densité de glaciers tropicaux se trouve dans la Cordillera Blanca des Andes péruviennes. Durant la saison sèche, l’eau issue de la fonte glaciaire est une ressource vitale, car celle-ci alimente jusqu’à 40% du débit des rivières. Les changements climatiques entraînant un retrait rapide des glaciers, l’approvisionnement de la population en eau potable de qualité devient une préoccupation sérieuse. L’objectif de ce mémoire est de faire le relevé de la qualité de l’eau dans le bassin hydrologique du Rio Santa, qui draine la portion occidentale de la Cordillera Blanca, en mettant l’emphase sur les éléments-traces métalliques potentiellement toxiques libérés par le drainage minier acide et par le drainage géologique naturel. En juillet 2011, des échantillons d’ions majeurs ont été récoltés dans 23 sites du Rio Santa et de neuf de ses affluents. Des échantillons d’éléments-traces métalliques ont quant à eux été récoltés dans 11 sites du Rio Santa et de 8 de ses affluents. Le pH, la température et l’oxygène dissout ont été mesurés sur place à tous les sites. Le débit du Rio Santa a été mesuré directement à 15 endroits et calculé par bilan massique pour 12 autres endroits. L’eau du bassin hydrologique du Rio Santa est caractérisée par une forte teneur en SO4, Ca et HCO3, dû à l’oxydation, naturelle et accélérée par les mines, des minéraux sulfureux et de la dissolution du carbonate. Le pH est approximativement neutre pour tous les sites sauf pour les affluents Rio Olleros et Rio Quilcay, qui ont tous deux un pH inférieur à 5. Un revêtement de Fe-oxyhydroxide recouvre le lit de ces affluents acides et quelques autres sites le long du Rio Santa. Les concentrations de As, Cd, Pb, Cu, Mo, Ni et U tendent à fluctuer au-dessus des niveaux de détection mais restent sous 10 ug/L pour la majorité des sites dans les bassins hydrologique. Des concentrations locales élevées apparaissent dans les affluents acides du Rio Olleros (70 ug/L de Ni) et du Rio Quilcay (82 ug/L, 27 ug/L, 34 ug/L and 14 ug/L de Pb, Cd, Ni et U, respectivement.) Des concentrations élevées ont aussi été trouvées dans les affluents dont le pH est approximativement neutre, soit le Rio Tabla (43 ug/L de Ni) et le Rio Llullan (720 ug/L de Mo et 180 ug/L de U.) Dans le Rio Santa, des concentrations élevées d’éléments-traces métalliques ont été détectées en aval des résidus de la mine Ticapampa (30 ug/L de As) et de la ville de Huaraz (73 ug/L, 58 ug/L, 53 ug/L, 40 ug/L et 23 ug/L de Pb, Cd, U, Mo et Ni, respectivement.) Le débit massique de ces éléments-traces métalliques de référence était près de zéro à la source du Rio Santa et tendait à augmenter graduellement au long de la rivière proportionnellement à l’augmentation du débit d’eau avec des grands pics de débits massiques d’éléments-traces métalliques à Ticapampa et Huaraz. La diminution dramatique de ses débits massiques après ces sites indique le comportement non-conservatif d’éléments-traces dissous dans les conditions de pH du Rio Santa. Alors que le débit d’eau de la saison sèche continue de décliner à cause du recul des glaciers, les problèmes de contamination actuels seront potentiellement exacerbés et des flux réduit empêcheront le Rio Santa et ses affluents d’agir comme tampon des affluents acides et des admissions d’eau résiduaires issue des mines. iii Acknowledgements Thank you to Dr. Jeffrey McKenzie for his dedication as a research supervisor. I have greatly appreciated his insight, availability, helpfulness, and good humor throughout the thesis process. Under his supervision I have learned so much and had a very positive grad school experience. Thank you to my former office mate, Dr. Michel Baraer, for assistance in planning and conducting field work, and for hours spent discussing my research and teaching me about hydrology. Dr. Sarah Fortner of Wittenberg University provided valuable assistance while I was getting started with trace metal research and continued to share her knowledge and datasets ever since, for which I am very grateful. Thank you to Bryan Mark of the Ohio State University for his role in project planning, field work, and data analysis. Thank you to Keith Hodson and Alex Eddie for much-needed ArcGIS assistance and sharing resources from their own research groups. Thank you also to Ollie Wigmore, Jeff Lafreniere, and Adam French for their help with field sampling. The other students in my research group have made it an excellent work environment and helped in many small ways over the years. Thanks to Danny Chavez, Rob Carver, and Laura Maharaj. Thank you to Anne Kosowski, Kristy Thornton, and Angela Di Ninno for keeping me on track all this time, answering my never-ending stream of questions, and making EPS such a great department. Similar thanks go to Brigitte Dionne for huge amounts of technical assistance. iv Preface The following thesis presents original research by the author at the Department of Earth and Planetary Sciences, McGill University during the 2011-2013 academic years. It is submitted in a traditional thesis format, and is ultimately intended to form a manuscript to be submitted to a peer-reviewed journal. This research was supervised by Dr. Jeffrey McKenzie from McGill University. Field work took place in the Rio Santa Watershed, Peru, in July 2011. Sample collection was done by a team of researchers, including the author, that were led by Dr. McKenzie and Dr. Bryan Mark from Ohio State University. Samples were analyzed at Ohio State University. Data was incorporated with pre-existing data sets collected principally by Dr. McKenzie and Dr. Mark since 1998, with additional data supplied by Dr. Sarah Fortner of the Wittenberg University. Analysis and interpretation of the data were done by the author at McGill University. v Table of Contents Abstract ............................................................................................................................. ii Resume ............................................................................................................................. iii Acknowledgements .......................................................................................................... iv Preface............................................................................................................................... v Table of Contents ............................................................................................................