Spatio-temporal distribution of pollen in Lake Väike-Juusa (South Estonia) sediments

The spatio-temporal distribution of the pollen preserved in the sediments of a small closed lake was studied in order to clarify the relationships between water level fluctuations and formation of pollen profiles. Pollen analysis and AMS 14C datings were performed on three sediment cores along a transect from the littoral zone to the lake centre. Pollen accumulation rates of dominant types of tree pollen (Picea, Pinus, Betula and Alnus) in every core were calculated for the last 6200 calibrated years and their relationships with the dynamics of morphometric parameters of lake depending on long term fluctuations in lake water level (dynamics of water depth at coring stations, dynamics of distances between the coring station and the nearest point on the lake shore, dynamics of lake area) were investigated. The results confirm that pollen accumulation rates are highest in the deepest part of the lake. Pollen distribution within the lake is species-specific and depends on the flowering season of the pollen source. Pollen originating from the trees flowering before the formation of the thermocline tends to have a higher accumulation rate in the deepest part of the lake. The pollen of trees flowering after the formation of the thermocline in the lake tends to have a higher accumulation rate in shallower water. These trends are positively correlated with water level fluctuations.