Chironomid paleo diet as an indicator of past carbon cycle in boreal lakes: Lake Kylmanlampi (Kainuu province; Eastern Finland) as a case study

Paleolimnology is a promising approach to reconstruct past carbon cycle in lakes and its response to global changes. Here, we test the potential of the combined use of sedimentary geochemical proxies and delta C-13 analysis of subfossil chironomid (delta C-13(HC)) in a sediment core retrieved from a boreal lake. Characteristics of sedimentary organic matter appeared to be strongly variable over time, corresponding to periodic decreases in aquatic organic matter contribution to lake sediments, and this dynamic was attributable to climatic changes occurring during the late Holocene. Results revealed also that delta C-13(HC) values were lower than those of organic matter, and these differences were greater when lake sediments were depleted in aquatic organic matter. Thus, chironomid feeding behavior seems to be dependent on the organic matter quality, showing a strong affinity for aquatic organic matter even if this resource is not the most available in sediments. Based on this methodological strategy, our results indicate (i) the relatively poor nutritive quality of allochthonous materials for benthic chironomid larvae, (ii) the strong influence of climate variability on the whole lake functioning, and (iii) the high potential of the combined use of this methodology to reconstruct the past carbon cycle in boreal lakes.