Functional paleoecology and allochthonous inputs in high latitude lake food webs

Abstract

Arctic freshwaters are subject to large scale changes triggered by ongoing climate change, including lengthening of the growing season, alterations of thermal regimes and biochemical rearrangements. Better understanding of biological responses to ongoing changes may rise from the past. This paleolimnological work examines functional assemblage structures and their diversity in high latitude lakes from subarctic Finland (spatial dataset of 25 lakes and a core from Lake Loažžejávri) and Arctic Canada (a core from Greiner Lake) in reference to long-term environmental change. Furthermore, responses of benthic functional assemblages to allochthonous inputs (carbon, nutrients), which are predicted to increase along the proceeding climate change, were investigated. In subarctic Finland, chironomid (Diptera: Chironomidae) functional feeding groups (FFG) were found to have different preference for nutrient and carbon based variables, suggesting that they are potential habitat indicators. Resource utilization of chironomids, as revealed by spatial and temporal stable isotope (C and N) modelling, was controlled primarily by availability of resources and secondarily by selective assimilation of different carbon pools, however no strong connection to FFG structure was detected. Regardless, allochthonous carbon input affected resource utilization by increasing allochthony and FFG distribution by habitat changes. External nutrient loads increased productivity in the study lakes, and from the ontogeny of Greiner Lake marine nutrients were found particularly important. This suggests that rising sea level, exposing low-lying coastal lakes to marine influence, may contribute to greening of Arctic from the aquatic perspective. These findings build towards better understanding of past food web functioning and associated responses to environmental change and altered energy flows under influence of multiple stressors. Keywords: Arctic; Chironomidae; environmental change; nutrients; organic carbon; resource utilization; stable isotopes