Quantifying arsenic post-depositional mobility in lake sediments impacted by gold ore roasting in sub-arctic Canada using inverse diagenetic modelling

Lake sediments are widely used as environmental archives to reconstruct past changes in contaminants deposition, provided that they remain immobile after deposition. Arsenic (As) is a redox-sensitive element that may be redistributed in the sediments during early diagenesis, for instance along with iron and manganese, and thus depth profiles of As might not provide a reliable, unaltered record of past deposition. Here, we use inverse diagenetic modelling to calculate fluxes of As across the sediment-water interface and interpret As sedimentary records in eight lakes along a 80 km transect from the Giant and Con mines, Northwest Territories, Canada. The sediment cores were dated using 210Pb methods and analyzed for solid-phase and porewater As, Fe, Mn and organic C concentrations. We reconstructed the history of As deposition by correcting for the varying mobility patterns and calculated contemporary As deposition fluxes. Correction for diagenesis was substantial for three of the eight lakes, suggesting that lakes with lower sedimentation rates, which allows longer residence of As within the reactive zones defined by the model, enhance the influence of diagenesis. Results show that solid phase As peaks coincides with the period of high emissions from past gold ore roasting activities. Results also show that sediments sustained present-day As fluxes to the water column of study lakes within 50 km of the mines, while sediment in study lakes further than 50 km acted as As sinks instead. [Display omitted] •Past As deposition to lake sediment assessed along 80-km transect from legacy mines.•Varying stratigraphic patterns of post-depositional As mobility were observed.•Inverse diagenetic modelling accounts for As mobility.•Modelled As fluxes match known temporal pattern of As emission from the mines.•Within 50 km, legacy As deposition continues to be released from sediment to water. Legacy arsenic deposition to lakes in the vicinity of a sub-arctic mine is inferred from the sedimentary record after correction for the influence of diagenesis.