14,000 years of climate-induced changes in carbon resources sustaining benthic consumers in a small boreal lake (Lake Tollari, Estonia)

In order to forecast the influence of future climate change on lake ecosystems, the paleolimnological approaches are needed to understand the impact of past climate variability. We reconstruct temporal changes in carbon resources sustaining chironomid biomass over the last 14,000 years, by means of carbon stable isotope analysis of subfossil chironomids (δ13CHC), with the aim of identifying the response of carbon processing in the benthic food web to climate change. We find a negative linear correlation between reconstructed summer mean air temperature and δ13CHC values, revealing that (i) the contribution of allochthonous organic carbon to the chironomid biomass is high during the coldest and low-productive period, (ii) the aquatic organic matter is the main carbon source during intermediate climate conditions, and (iii) a significant part of the chironomid biomass is sustained by methane-derived carbon during the Holocene Thermal Maximum and the Bølling-Allerød. This study confirms that climate change may significantly affect the recycling process of organic carbon in the benthic food web of small lakes. However, deforestation and agricultural practices within the catchment area induced important organic matter inputs into the lake sediments, which seem to disrupt the observed relationship between climate variability and carbon processing in the benthic food web. In this context, complementary studies are needed to better understand the combined effects of the ongoing global warming and human activities on the lake carbon cycling.