In the lake-rich tundra uplands east of the Mackenzie Delta, almost one in ten lakes has been affected by retrogressive thaw slumping. In this study, we assessed water chemistry for 34 slump-affected and 39 undisturbed upland lakes across this region and found that environmental factors typically evoked to explain variation in tundra lake water quality including surficial geology and proximity to the treeline or coast were subordinate to the main driver, permafrost degradation. Thaw slump-affected lakes had elevated ionic concentrations and water clarity in comparison with undisturbed lakes. The strength of the ionic impact was positively associated with the proportion of catchment affected by slumping and inversely related to disturbance age. Slumping did not have a significant effect on total organic carbon (TOC) concentrations, although Water clarity increased significantly with decreasing age of disturbance. In lakes undisturbed by slumping. fire-induced active-layer deepening had a delectable influence on lake water ionic strength. Surficial deposits influenced TOC concentrations with the highest concentrations and colour in undisturbed lakes with lacustrine catchments. In a warming Arctic, thermokarst processes may increase in importance as a driver of ionic chemistry and optical properties of small lakes and ponds, and shifts in aquatic food webs can be anticipated. Copyright (C) 2009 John Wiley & Sons, Ltd. and Her Majesty the Queen in right of Canada.

Chemical data are presented for water from 22 lakes in small upland catchments (<20 ha) between Inuvik and Richards Island, Northwest Territories, Canada. Eleven of the basins appear pristine and I I are affected by thermokarst slumping. The mean dissolved organic carbon (DOC) concentration of the pristine lakes (16.3 mg/l) is greater than the mean concentration of lakes disturbed by thermokarst slumping (10.5 mg/l). In pristine lakes, mean concentrations of Ca, Mg and SO4 are 9.6, 3.6 and 11.1 mg/l, but in lakes affected by thermokarst, mean concentrations are 72.6, 26.8 and 208.2 mg/l, respectively. Soluble materials released from degrading permafrost are transported to lakes by surface runoff, elevating concentrations in lake water. The percentage of total basin area influenced by thermokarst is positively associated with ionic concentrations in lake water and inversely related to DOC. Thermokarst occupying as little as 2% of catchment area may modify the chemistry of lake water, and water quality may remain affected for several decades after slump development has ceased. Aerial photographs indicate that 5 to 15% of all lakes and ponds in four 49 km(2) areas between Inuvik and Richards Island are small (median size <2 ha) with catchments affected by thermokarst. Copyright (C) 2005 John Wiley & Sons, Ltd.