Revisiting pollen accumulation rates from Swedish lake sediments

Early hope that the estimation of pollen accumulation-rates (PAR) from lake sediments would permit the quantitative reconstruction of past vegetational composition abated when results from several experiments uncovered the problems of the method. A review of monitoring experiments, mainly conducted between 1960 and 1980, shows that basin size, transport of pollen with flowing water and sediment redeposition and focusing are the most important factors influencing pollen deposition in lakes. With careful site selection most of these factors can be rendered unimportant or constant. It is shown that PAR estimates from three small lakes in a rather homogeneous forest region are very similar for the last 9000 years. Results from monitoring of pollen deposition in pollen traps provides important information in the interpretation of PAR. Monitoring experiments were conducted to explore the deposition of pollen on and in small lakes. Pollen deposition in pollen traps floating on small lakes was not different from pollen deposition observed on land. PAR estimates from lake sediments were comparable with the results of pollen monitoring obtained with Tauber-type traps. A proportion of airborne pollen deposited on a lake surface is lost during the transport to the lake sediment. The amount of pollen that is lost differs between pollen types.