Recent stratigraphy and accumulation of sediment in the deep, oligotrophic Lake Pääjärvi in South Finland

Abstract

Laminated sediment is deposited in the deep areas (> 30 m) of Lake Pääjärvi. In the diatom microstratigraphy a regular alteration of planktonic and littoral floras, which goes in pace with the visual structure, reflects the yearly cycle of sedimentation.

Considerable variation in sedimentation was found to have occurred during the past two decades. A sequence, dated to the early 1960's, in which the organic content was exceptionally high, could be identified in the sediment at 6–14 cm depth even in shallower areas where laminations are not formed. This level was used as a marker horizon when determining the recent distribution of sediment by means of 19 cores taken from different parts of the lake.

The average annual sediment accumulation in the profundal zone of the lake is 340 g m⁻²a⁻¹ dry weight, of which 25 g m⁻² a⁻¹ (1100 kJ m⁻² a⁻¹) is organic carbon.