Climate versus in-lake processes as controls of the development of community structure in a low-arctic lake (South-West Greenland)

The dominant processes determining biological structure in lakes at millennial timescales are unclear. In this study, we used a multi-proxy approach to determine the relative importance of autogenic versus allogenic processes on the Holocene development of an oligotrophic lake in SW Greenland (66.99º N, 50.97º W). A 14C and 210Pb-dated sediment core covering ~8400 years BP was analysed for organic-inorganic carbon content, pigments, diatoms, chironomids, zooplankton and stable isotopes (13C, 18O). Relationships among the different proxies and a number of independent controlling variables (Holocene temperature, the 8.2 Kyr event, and immigration of Betula nana into the catchment) were explored using redundancy analysis (RDA) independent of time. The main ecological trajectories in the lake biota were captured by ordination first axis sample scores (18 – 32% variance explained). The importance of the arrival of Betula (ca. 6500 yBP) into the catchment was indicated by a series of partial-constrained ordinations, uniquely explaining ~15% of the variance in chironomids and ~9% in pigments. Climate influences on lake biota were strongest during the 8.2 Kyr cooling event, when all proxies responded rapidly although only chironomids had a unique component (in a partial-RDA) explained by the 8.2 Kyr event (8%). Holocene climate explained less variance than either catchment changes or biotic relationships. The sediment record at this site indicates the importance of catchment factors for lake development, the complexity of community trends even in relatively simple systems (invertebrates are the top predators in the lake) and the challenges of deriving palaeoclimate inferences from sediment records in low arctic freshwater lakes