Permafrost degradation has been implicated as a dominant control on riverine mercury fluxes in arctic watersheds. However, the importance of permafrost thaw on fluxes of mercury, methylmercury, and trace metals such as lead-relative to other geomorphic and hydroclimatic controls-remains unclear. To investigate these controls, we conducted -weekly water chemistry sampling at the mouth of the Old Crow River, a pristine, 13,900 km(2) watershed in arctic Canada underlain entirely by continuous permafrost. Mercury, methylmercury, and lead concentrations were low on average (similar to 2 ng/L, 0.04 ng/L, 0.8 mu g/L, respectively), and peaked during the freshet (< 7 ng/L, 0.11 ng/L, 11 mu g/L, respectively). The trace elements had strong positive association with suspended sediment, and were mobilized during periods of high discharge (freshet and rainfall). Summer time sampling of major tributaries and at thaw slumps revealed that trace element concentrations were not elevated downstream of thaw slumps or thermokarst lakes across the watershed. Ubiquitous thermokarst in the Old Crow basin did not result in anomalously high catchment-scale concentrations, fluxes, and yields of mercury, methylmercury, nor lead. Rather, warming-driven increases in precipitation and elevated discharge during freshet and rainfall promoted permafrost and talik river bank erosion. This erosion, which was controlled by landscape and geomorphic factors, supplied short-lived increases in particle-bound trace element flux.
