Report: Balea Lake – Chironomid Analyses

From September 2023 to June 2024, a detailed study of chironomids was carried out on the core from Balea Lake (Southern Carpathians, Romania). A total of 112 samples were processed in the laboratory and analysed under a microscope to study the chironomid head capsules and species composition. Later, 15 more samples of the recent community of chironomids were taken from the lake with the aim to examine chironomid larvae and pupal exuvia. This work is part of a broader multiproxy analysis aimed at reconstructing Holocene climate and environmental changes in the region.

Chironomids were used for ecological reconstruction and to infer mean July air temperatures over the past 8,600 years. For the first time, two training sets, the Swiss-Norwegian and Finnish-Polish-Carpathian, were used together for temperature reconstructions. In total, 41 chironomid taxa from Orthocladiinae, Tanytarsini, Tanypodinae, Diamesinae, and Prodiamesinae were identified. The structure of the chironomid assemblages suggests that cold, oligotrophic conditions dominated throughout the Holocene, with a notable shift around 4,200 years BP. This shift coincides with the 4.2 ka climatic event, characterized in this region by increased precipitation and a shift in sediment composition. It also led to more frequent debris flows, which altered the lake’s environmental and sedimentary conditions. Human impact became more pronounced over the last 1,200 years, further influencing the chironomid assemblages.

The recent chironomid community in the lake is represented by 14 taxa. Among these, cold oligotrophic taxa are still common, but several taxa with wider tolerance suggest a warming trend and environmental changes in the last decade. The results of the chironomid analysis from Balea Lake will soon be published in a scientific journal.