Holocene vegetational and limnological changes in the Fennoscandian tree-line area as documented by pollen and diatom records from Lake Tsuolbmajavri, Finland

A 291 cm sediment core was taken from Lake Tsuolbmajavri in the Finnish tree-line area. The core was dated by means of 14 AMS C-14-dates. Pollen data indicate that during the early-Holocene the catchment was characterized by birch forest. Gradual expansion of pine started at 9200 cal BP. Pine reached its maximum occurrence at 7200-6000 cal BP and pine tree-line retreated from the area at 4600 cal BP. During the late Holocene, the cooler and moister climate led to increasing peatland development in the catchment. The influence of vegetation dynamics on the limnology of the lake was investigated by means of diatom-stratigraphical data. The increasing total organic carbon (TOC) concentration, water color, and decreasing pH from 8500 cal BP to 6000 cal BP reflect the gradual development of forest and more humic soil. The disappearance of pine caused a slight rise in pH and a decrease of TOC and water color values. At 3000 cal BP, TOC concentrations and water color started to increase again. This change is synchronous with the rise of Sphagnum spore influx values and may reflect the impact of peatland expansion on lake water quality. The results suggest that the catchment vegetation patterns, mainly tree-line dynamics and peatland distribution, have influenced the limnological features of Lake Tsuolbmajavri.