Subfossil chironomid stratigraphy of a small acid lake in southern Finland

Olander, Heikki: Subfossil chironomid stratigraphy of a small acid lake in southern Finland. Bull. Geol. Soc. Finland, 64, Part 2, 183—188. Chironomid analysis was used to study ecological changes in shallow oligotrophic Lake Orajarvi in Espoo, southern Finland. A 53 cm long sediment core for chironomid analysis was obtained at 6 m depth. Changes in chironomid composition of the Lake Orajarvi are related to temperature changes and anthropogenic acidification. Decline of Microtendipes and emergence of Heterotrissocladius at 30—35 cm depth are due to deteriorating climate after Holocene climatic optimum. Most recent changes in chironomid fauna can be related to strong human induced acidification of the lake, which has led to domination of Dicrotendipes and Psectrocladius. Chironomid analysis, which mostly has been used in deep stratified lakes, seems to be a valid method also in shallow unstratified lakes.