Insights into pollen source area, transport and deposition from modern pollen accumulation rates in lake sediments

Abstract

Pollen accumulation rates (PAR) from late Quaternary deposits can provide direct estimates of past plant abundance. They are influenced by lake internal processes and therefore rarely used in between site comparisons, although few studies from Fennoscandia have applied them successfully. This study aims to explore how PARs from selected lakes from Northeast Germany reflect differences in plant abundance as a step towards quantitative vegetation reconstructions from PARs.Short sediment cores were collected from 18 lakes of which 16 could be dated by 210Pb. PARs were estimated for the youngest sediment, representing approximately two years before sampling in 2009, and samples dated to around 1993. Forest inventory data for the two time slices were obtained for 15 km around the sites and standing volume (SV) was estimated as a measure of above ground biomass. PARs were compared to the total SV within increasing areas around the lakes, as well as to distance-weighted SV using the Prentice/Sugita model of pollen dispersal and deposition. Both assessments of the vegetation data yielded strong linear relationships with PARs already over distances of tens of metres to a few kilometres documenting the importance of the local vegetation. This indicates the importance of the often neglected trunk space component of pollen transport for small lakes. Results from the small number of large lakes suggest that these sites receive a larger absolute input of pollen from regional sources. These observations indicate that small lakes may be somewhat sheltered from pollen transported above the canopy.We demonstrate that PARs of the major tree taxa obtained from lake sediments are linear related to the lake surrounding biomass. This confirms that PAR can be used to infer past changes in plant biomass, although absolute pollen deposition may also be determined by net primary productivity of the biomass.