Modern pollen assemblages from surface lake sediments in northwestern China and their importance as indicators of vegetation and climate

The modern pollen assemblages of surface lake sediments and topsoils in northwestern China were studied to understand the relationship of modern pollen data with contemporary vegetation and climate, and the differences between the pollen assemblages of surface lake sediments and topsoils. The results show that Chenopodiaceae and Artemisia are dominant elements in the pollen assemblages of northwestern China. Additionally, Ephedra, Cyperaceae, Asteraceae, Poaceae, Picea, Pinus, and Betula are also important pollen taxa. Both pollen assemblages and principal component analysis indicate that pollen data from surface lake sediments and topsoils can be used to differentiate the main vegetation types of this region(desert, steppe, meadow and forest). However, differences exist between modern pollen assemblages of the two types of sediments due to the different relevant source areas of pollen and degrees of pollen preservation. For example, the larger relevant source area of surface lake sediment results in a higher abundance of Betula in pollen assemblage from surface lake sediment, whereas the tendency to disintegrate thin-walled pollen types in topsoil leads to a higher proportion of resistant pollen, such as Asteraceae. Linear regression analysis indicates that the Artemisia/Chenopodiaceae(A/C) ratio in pollen assemblages of surface lake sediments can be used to indicate humidity changes in the study area. However, the A/C ratio in topsoils should be used carefully. Our results suggest that pollen data from surface lake sediments would be better references for interpreting the fossil pollen assemblages of lake cores or lacustrine profiles.