Land use and climate change impacts on lake sedimentation rates in western Canada

Fine sediment derived from catchment erosion can adversely impact aquatic ecosystems. Previous studies of lake sediment deposits in western Canada attributed increased sedimentation to land use; however, high catchment variability and short- and long-term climatic responses complicated the interpretation of those regional records. We compiled a large inventory of lake catchment data transecting the Canadian cordillera that comprised ²¹⁰Pb-based profiles of deposition, GIS-based land use records, and interpolated climate change data. We used these data and mixed-effects modeling to relate sedimentation trends to land use and climate change since the mid-20th century. Although sedimentation was highly variable, increasing trends in accumulation corresponded with cumulative land use and, to a lesser degree, with climate change. Road density was the most important variable, but the inclusion of timber harvesting density further improved model fits significantly. Land use effects were more difficult to discern for the easternmost region of the Alberta Plateau where sedimentation appeared to be cumulatively associated with both timber and energy resource extraction. Stronger relations were obtained with whole catchment (0.50-273 km²) measures of land use, suggesting that fine sediment is efficiently transferred from hillslopes to the lake basins. While accounting for land use, a climate signal was also detected with improved model fits obtained with the inclusion of catchment warming. Further modeling results suggest that at least one critical control of reconstructed sedimentation remains undetermined. Interdecadal rates of lake sedimentation in western Canada have steadily increased during the late 20th century, following patterns of regional environmental change.