Étude spatio-temporelle de la contamination en métaux traces du Rio Santa, Pérou

Abstract

The Santa River in Peru drains the western slopes of the glacierized Cordillera Blanca and provides water resources at almost all levels of the watershed, directly or indirectly benefiting 1.6 million people. As it flows away from the valleys of the Cordillera Blanca, the Rio Santa takes out trace metal from numerous sources. Previous studies on trace metal in the watershed have mainly been limited to specific areas, metals and /or seasons and to dissolved elements, not providing a comprehensive view of the concentration levels at the watershed scale. The objective of this research is to characterize the spatiotemporal variability of trace metals in the Rio Santa watershed. To that end, we propose an original combination of methods based on water, suspended sediments and river bed sediments collection at different points of the watershed. From June 21 to July 8, 2013, 40 points across the Rio Santa watershed were sampled. In addition, water samples were collected at a single location on the Rio Santa. Both total and sequential extraction methods were applied to the river bed sediments to better understand transfers between tributaries and the Rio Santa. Samples were then analysed using ICP-MS, ICP-OES and AAS. Overall, the results show that the Rio Santa water is contaminated with Mn at more than 50% of the sampling points. Sediments collected in the Santa river bed were heavily contaminated by at least four of the tested elements at almost 85% of the sampled spots. We observed an absence of a dilution effect in the Rio Santa during the wet season. This suggests that the trace metal concentration in water might be governed by ion exchange processes between the liquid and solid phases. In addition, our results suggest that Trace metal concentration in the sediments probably originates from transfers of particles from contaminated tributaries to the Rio Santa. Our results show that the original combination of methods we tested allows for a complete assessment of the trace metals concentrations spatiotemporal variability at the scale of a watershed.

Date	19 Feb 2016
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Michel Baraër (Supervisor)