Long-term ecosystem dynamics of a small lake and its catchment in west Greenland

We investigated the interplay between climate and the Holocene ecological development of a small low-Arctic lake and its catchment. The remains of terrestrial and aquatic oribatid mites, plant macrofossils, and other invertebrates in a sediment core from Lake SS16 in west Greenland revealed its palaeoecological history over the last 6950 years. Betula nana immigrated into Dryas fell-field and open grassland around 6600 cal. yr BP and then expanded to dominate dwarf-shrub heath that clothed the catchment for 4800 years. Like other lakes in Greenland, the mesotrophic SS16 became progressively oligotrophic as a consequence of nutrient depletion and reduced runoff from the maturing catchment vegetation. Abrupt declines of Lepidurus arcticus and Daphnia probably reflect the immigration of fish around 6300 cal. yr BP. After c. 2000 cal. yr BP, catchment heathland declined with Neoglacial cooling and reduced precipitation and was replaced by open Dryas grassland vegetation and bare soil. Lake productivity also decreased. The major early-Holocene catchment changes pre-date the aquatic changes, revealing decoupling of ecological responses to climate. In the late Holocene, however, climate change was the predominant driver in both lake and catchment. This multiproxy study shows the valuable contribution made by oribatid mites in the reconstruction of direct processes (e.g. precipitation:evaporation ratio), indirect processes (e.g. nutrient sequestration by maturing tundra vegetation, immigration of taxa), and internal feedbacks (e.g. trophic interactions) that controlled ecosystem development in the past.