Combining limnology and paleolimnology to assess the influence of climate change on two lakes in Southern Greenland

We aim at understanding the influence of climate change on the functioning of two freshwater lakes in South Greenland by combining limnological and paleolimnological methods. The results offer a means of testing the potential use of subfossil chironomid for paleoclimate reconstruction. First, the current ecological status of Lake Igaliku and Lake 95 has been assessed by the combined use of a biotic index and δ15N analysis of chironomid larvae. The current ecological state of Lake 95, as a remote lake exempt from local human activities, remains pristine. In contrast, Lake Igaliku exhibits a worrying ecological state characterized by the disruption of the nitrogen cycle, a loss of littoral biodiversity, and alterations of its trophic functioning. A paleolimnological approach, combining subfossil chironomid and geochemical analysis, was applied to reconstruct the ecological trajectories of the lakes over the last 150 years. Redundancy analysis performed on chironomid assemblages shows that the two systems are partially driven by climate variability, and underscoring the strong potential of chironomid remains for paleoclimatic reconstruction. However, local farming activities in the catchment area of Lake Igaliku have strongly impacted its ecological state since the late 1980s, masking the actual effects of the current global warming. In conclusions in southern Greenland, lakes in pristine conditions may be excellent candidates for the past climate reconstructions based on subfossil chironomids.