Over-representation of Picea pollen induced by water transport in arid regions

Picea pollen plays an important role for reconstructing a cold-humid climate or palaeo-elevations. However, research has not yet taken into account the pollen transportation pathways within rivers in arid regions. A sporopollen study of surface (the uppermost) river sediments and surface soils from the Heihe and Shiyang Rivers (originating in the Qilian Mountains) suggests that significant differences exist between Picea pollen percentages within these two different sediment types. In surface soils the Picea pollen fractions are low, representing transportation by wind. However, percentages of Picea pollen reach up to 15.9% of total pollen counts in surface river sediments, as far as about 120 km away from the lower spruce forest line. This result, together with the demonstrated enrichment of Picea pollen in water bodies that lie along those observed rivers, indicate an over-representation within fluvial and lacustrine sediments. Knowledge about these relationships provides fundamental information for the reconstruction of palaeo-vegetation, palaeo-climate or palaeo-elevations.