Trace Metal Stream Contamination in a Post Peak Water Context: Lessons from the Cordillera Blanca, Peru

As a result of climate warming and glacier recession, glacierized watersheds will experience a decrease in dry season discharge and an increase in wet season discharge, with negative consequences for water quality. The glacierized Rio Santa watershed in Peru provides a unique opportunity to study these concerns, because it drains the mountain range with the highest density of glaciers in the tropics. The mountain range has already passed peak water due to glacier retreat, and previous studies have reported high concentrations of dissolved trace metals in the Rio Santa. During summer 2013, 40 sites along the Rio Santa watershed were sampled for river bed sediments. In addition, water samples were collected at a single location in the Rio Santa over a period of 1 year. A sequential extraction was performed on the sediments and analyzed for Al, As, Cd, Fe, Pb, and Zn concentrations. Results show a chemostatic behavior of studied trace metals and present comparable distributions of metals among phases in the Rio Santa and its tributaries. These results suggest that at least a portion of the surface sediment contamination from trace metals originates from a transfer of primary particles from contaminated tributaries. In a post peak water context, this study implies that the increase in wet season discharge related to glaciers may represent a risk of contamination spread associated with sediment transport enhancement.