A test of the integrity of metal records in sediment cores based on the documented history of metal contamination in Lac Dufault (Québec, Canada)

There is an important volume of published information on Lac Dufault (Québec) which describes the history of metal inputs over 70 years and the changes that occurred in the lake as a result of this contamination. We used this abundant source of chronological markers to test the hypothesis that lake sediments can provide true historical records of trace metal loading from metal mining. Sediment cores were obtained from the deepest zone of the lake (19 m). The sediments were dated using ²¹⁰Pb and ¹³⁷Cs and they were analyzed for total elemental concentrations (Ca, Cd, Cu, Fe, P, Pb, S, Zn). Metal profiles in the sediment core preserved the distinct signatures of different mine exploitations documented in the lake watershed. In particular, the core recorded: the beginning of industrialization in 1926; increasing sedimentation rates associated with perturbations in the lake watershed; the maximum of sediment [Cu] and the contemporary exploitation of ore bodies rich in Cu; the maximum of sediment [Fe] and the contemporary production of pyrite by a mining operation; the low sediment [Cu] and [Zn] in the 1950s and the low contemporary production of these metals by mining operations; the maximum of sediment [Cd] and the contemporary production of Cd by a subsequent mining operation. Anomalies in the distribution of ²¹⁴Pb activities in sediments reflected the intensity of acid mine drainage (AMD). There is good evidence that the lake resisted acidification from this AMD for the last thirty years. Overall, our results support the thesis that profiles of sedimentary Cd, Cu, Zn, Pb and Fe levels reflect the past history of metal input to Lac Dufault.