Distribution and sources of fluvial pollen in the middle reaches of the Yellow River in China and their relationship with vegetation and land use

Understanding the processes determining the composition of alluvial pollen assemblages and its relationship with wa-tershed vegetation is a prerequisite for alluvial palynological study. Palynological analysis of a total of 45 river water samples collected from the middle reaches of the Yellow River and its major tributaries, identifies the distribution pat-terns, possible sources of pollen and relationship with the catchment vegetation. The results reveal that the pollen as-semblages in the middle reaches of the Yellow River is dominated by herbaceous taxa, and the pollen is mainly derived from fluvial sources. Higher concentrations of the pollen tend to occur in the southern part of the study area. The Luo River is the main source of tree pollen in the Wei River Basin, while the Sanchuan River and Xinshui River are the main sources of tree pollen in the mainstream of the Yellow River. Herbaceous pollen mainly originates from the flood plain, and from channel bars and point bars, and there is no obvious relationship between herbaceous pollen and tributary inputs. The relative proportions of the various land use classes in the middle reaches of the Yellow River can be ordered as follows: grassland (GL) > cultivated land (CL) > forest (FO) > shrubland (SH) > water (WA). The herbaceous pollen of the Huangfuchuan River and Kuye River are closely related to the coverage of GL; cereal pollen is not fully representative of the CL coverage in the watershed; and the pollen of woody plants is extremely over-represented com-pared to the coverage of FO and SH in the watershed. Our results provide basic information about the sources of fluvial pollen and its indicative significance in the lower Yellow River and they are also potentially applicable to other major river basins.