A multi-proxy palaeoecological study of Alanen Laanijarvi, a boreal-forest lake in Swedish Lapland

Chironomids, pollen and spores were used to reconstruct Holocene aquatic and terrestrial environments at Alanen Laanijarvi, northern Sweden. Chironomid analysis revealed a pattern of limnological evolution from oligotrophic conditions in a relatively deep lake during 8.6 to 5.5 cal. ka BP, followed by a period of lake shallowing from 5.5 to 2.7 cal. ka BP. Increases in acidity and littoral habitat complexity may have occurred from 2.7 cal. ka BP to the present, though some compositional changes may have resulted from human disturbance. Chironomid-inferred mean July air temperatures range between 9.8 degrees C in the Early Holocene to 11.3 degrees C in the Late Holocene. Limitations on chironomid-based quantitative temperature interpretations may exist because of low taxon richness. Diatoms were recovered from the upper sediments only, from about AD 1800. Pollen and spore analysis revealed an early colonizing vegetation of juniper, sedges and birch soon after local deglaciation, followed by birch forests until about 8.3 cal. ka BP. Alder stands occurred locally to 5.5 cal. ka BP, when pine and spruce forests developed and remain to the present day. These results suggest that little major terrestrial vegetation change may occur in some northern environments with predicted future global warming, where it is predicted to be most severe. Aquatic environments may, however, be greatly affected by a shift in precipitation regime, causing changes in allochthonous organic input, lake depth and possibly the amount of human activity or disturbance in the watershed.