Distribution of chironomids (Diptera) in low arctic West Greenland lakes: trophic conditions, temperature and environmental reconstruction

1. Surface sediment samples of subfossil chironomid head capsules from 47 lakes in southern West Greenland were analysed using multivariate numerical methods in order to explore the relationship between chironomid assemblages and selected environmental variables. The study lakes are located along a climate gradient ranging from coastal maritime conditions near the Davis Strait to a continental climate near the margin of the Greenland ice sheet. 2. High-resolution surface water temperatures were measured through the summer season using automatic data loggers in 21 of the study lakes. The mean July surface water temperature (1999) ranged from 7.3 to 16.5 degreesC in the data set. 3. In all lakes, a total of 24 chironomid taxa were recorded; Micropsectra, Psectrocladius, Chironomus and Procladius were the dominant genera. There was a strong correlation between the trophic variables [total nitrogen and total phosphorus (TN, TP)] and temperature, and in redundancy analysis (RDA) the three variables explained almost equal significant amounts of variation in the chironomid data (19.8-22.3%). However, temperature lost significant explanatory power when the effect of TN was partialled out in RDA. 4. The lakes were classified using two-way indicator species analysis (TWINSPAN) into eight groups defined by temperature, trophic variables, salinity (conductivity) and lake-morphometric data. Fourteen chironomid taxa showed significant differences in percentage abundances among groups, with Heterotrissocladius, Micropsectra, Ablabesmyia and Chironomus as the most robust group-indicator taxa. Forward selection of taxa in multiple discriminant analysis was used to fit chironomid assemblages into lake groups. Using only eight taxa, 95% of lakes were correctly classified at a second TWINSPAN division level (four groups) and 85% of lakes at a third division level (eight groups). 5. This study showed that there is considerable potential in using subfossil chironomid head capsules as paleoenvironmental indicators in both short- and long-term (down-core) studies of lake ontogeny and palaeoclimate conditions in West Greenland. However, because of the strong correlation between temperature and trophic variables, a quantitative reconstruction of lake- and habitat-type is recommended, in combination with direct reconstruction of single variables such as temperature.