The distribution of freshwater Chironomidae (Insecta: Diptera) across treeline near the lower Lena River, northeast Siberia, Russia

Surficial sediment from 31 lakes along a transect spanning treeline in northeast Siberia was analyzed for midge remains in order to assess the modern distribution of midges relative to treeline. Taxa distinct to tundra, forest-tundra, and forest areas were identified. Abiskomyia, Parakiefferiella nigra, and Hydrobaenus/Oliveridia were found predominantly in tundra lakes, whereas Zalutschia zalutschicola and Microtendipes were restricted to forest-tundra or forest lakes. A sharp delineation exists at the tundra/forest-tundra transition zone with respect to the genus Corynocera. Corynocera oliveri was found chiefly in tundra lakes whereas C. ambigua was found solely in forested areas. Thirty-two environmental variables describing the physical, chemical, and limnological characteristics of the lakes in the transect were measured. Redundancy analysis (RDA) revealed that statistically significant relationships exist between chironomid distributions and six of the measured environmental variables (particulate organic carbon, particulate organic nitrogen, iron, zinc, lake depth, and Secchi depth), but not surface lake-water temperature. Canonical variate analysis (CVA) demonstrated that chlorophyll a, lake depth, pH, and strontium maximized separation of tundra, forest-tundra, and forest lakes from one another. These results illustrate the importance of treeline as an ecological boundary for the distribution of chironomids. The abrupt changes in distribution that occur at treeline for specific chironomid taxa suggest that subfossil chironomid analysis may be used to infer past changes in the position of treeline.