Chironomid-based classification of lakes in western Finnish Lapland

For the implementation of the Water Framework Directive we need to develop an informative and cost-effective set of biological monitoring and assessment methods, especially for remote areas. Chironomids are known to be an abundant and species-rich group that dominate the aquatic macroinvertebrate assemblages in the north and therefore should be an integral part of monitoring and assessment plans. In this paper, we aim to characterise lake types in subarctic Finnish Lapland using particular chironomid indicator taxa. Contemporary chironomid assemblages and 24 corresponding physical and chemical limnological variables were determined for 63 lakes. Among them, fifty shallow lakes (<= 10 m) were classified into biological lake groups using Two-Way Indicator Species Analysis (TWINSPAN). The environmental variables best discriminating between the groups were determined using canonical variates analysis (CVA). Classical lake typology was additionally applied to 13 deeper lakes. Among the shallow lakes, three lake groups were separated on the basis of their chironomid assemblages: (i) small and shallow organic-rich lakes, (ii) large and base-rich lakes, and (iii) cold and clear oligotrophic tundra lakes. The deep lakes were all, except one, oligotrophic. The degree of oligotrophy was related to temperature. The results indicate that the classification of shallow lakes using chironomid communities is a useful tool for developing a lake typology and in assessing and monitoring the remote subarctic lakes.