Pollen profile from sediment core Roxheimer Altrhein

Stratigraphy: 0-0.05 m peaty clay, 0.05-0.9 m sand, 0.9-1.1 m sandy clay, 1.1-1.84 m clay, 1.84-2.06 m sand, 2.06-3.1 clay, 3.1-3.2 m clay with fine sand, 3.2-3.63 clay (above sand)
A proper interpretation of the pollen data has to consider that the site was originally a meander of the river Rhine which was cut off from the main stream and thus became an oxbow lake. Accordingly the profile should consist of fluvial sediment in its lower part and of lacustrine sediment further up. The distribution of the pollen grains of Picea and Abies throughout the profile parallels the expected change of sediment. Although both tree species have never grown in the area during the Holocene, but stayed restricted to the mountainous regions further south (e.g. the Black Forest), their pollen is found in rather large quantities in the lowermost samples of the profile. It is almost absent further up. The two pollen types can easily swim. Therefore the distinct decrease of their frequencies most likely reflects the change from fluvial to lacustrine conditions. The few pollen grains of Picea and Abies in ''post-fluvial time'' samples were brought to the site by the occasional aestival floods and of course by the wind. The distribution of the pollen grains of aquatic and swamp plants - frequent in the samples with little pollen of Picea and Abies - confirms this interpretation and reflects the silting up of the lake.