Evaluation of limnological responses to recent environmental change and caribou activity in the Riviere George Region, northern Quebec, Canada

The influence of natural terrestrial disturbances on the limnology of northern lakes is little known, yet important for understanding the ecology of these remote ecosystems. The Riviere George Caribou Herd (RGCH) in northern Quebec has undergone a large population increase since the 1950s, which has been accompanied by pronounced impacts (i.e., degradation of vegetation cover, soil erosion) on terrestrial environments of the Riviere George region. The goal of our study was to evaluate if the increased caribou activity and resulting terrestrial impacts have been accompanied by impacts on adjacent aquatic ecosystems. We studied the recent diatom assemblages (i.e., about the last two centuries) preserved in six sediment cores taken from lakes located in the most heavily impacted region, and in one core from a lake showing little evidence of recent caribou activity in the catchment basin. Core chronologies based on Pb-210 dating techniques indicated that average mass sedimentation rates in this subarctic region were very low (0.0039 to 0.012 g cm(-2) yr(-1)). Perhaps surprisingly, diatom assemblages from all seven cores showed very little change, indicating remarkably stable limnological conditions throughout the past similar to200 yr. The lack of a signal from caribou activity is most likely due to (1) short-term impacts being too transitory to be registered in the sediment record, and (2) long-term impacts not representing a significant perturbation outside the natural variability of these aquatic ecosystems. In contrast to other arctic regions, the limnological stability of our study sites suggests that recent climatic change impacts have been negligible in this region of northern Quebec, which seems to confirm climate model predictions that northern Quebec and Labrador will remain climatically stable under global warming scenarios.