Airborne Palynological Assemblages In The Suburb Of Lanzhou And The Effect From Special Weather

The airborne pollen is an important information carrier to the change of climate and process of environment and the process of change. The characters of airborne palynological pollen assemblages and the sporopollen influx are changed with the vegetation composition, location, weather condition and other factors of a region. Therefore, discussion of the spatial distribution and change of major airborne pollen types in an area and their relationship with the regional vegetation of the modern airborne pollen are important parts in modern pollen process research. The pollen is one of an important proxies for reconstructing paleo-vegetation environment of in the Loess Plateau. To do that well, it is very important to know more clear about the modern pollen process. Lanzhou is one of typical sites in the loess plateau region. Airborne pollen assemblages and dispersal characters in Lanzhou area are representive in the loess plateau.In this paper, the airborne sporopollens were collected by pollen traps in the suburb and urban areas of Lanzhou. Pollen traps are put in different heights in these two sites. Meanwhile, the airborne sporopollens were also collected separately in duststorm days and rainy days at the Lanzhou suburb. The difference of pollen types, pollen influx and pollen assemblage characters are compared in different climatic conditions and different sampling heights. In addition, they are also compared with local vegetation, by which we can reveal the pollen dispersal characters and the relationship between pollen and vegetation in different sample sites and different seasons. The difference of pollen assemblages between special weather (duststorm days and rainy days) and the normal weather in the similar period were analyzed to reveal the pollen sources and transportation characteristics of main pollen types.The comparision results of the airborne palynological pollen assemblages characters in Lanzhou urban and suburban shows that the main pollen types in the two sites are consistent, with Ulmus, Cupressaceae, Pinus, Populus, Ostryopsis, Rosaceae, Elaeagnus, Ephedra, Artemisia, Chenopodiaeeae, Gramineae, Compositae, Ranunculaceae and Leguminosae as the major pollen types. The results also indicate that the airborne palynological pollen assemblages have some differences between suburb and urban of Lanzhou,though both of them can reflect the regional vegetation characters well. While,there are some differences of airborne palynological assemblages between suburb and urbanof Lanzhou, for examples, the percentage of Cupressaceae, Populus, Parlhenocissus andother cultivated pollen are higher in the urban area than that in the suburb area. Which arecaused that human plants more Platycladus orientalis , Populus alba and Parthenocissusquinquefolia in city. While, the percentage of Ulmus pollen are higher in the suburb area thanthat in the urban area, becouse Ulmus pumila is one of scarce arbors that can live well insteppe areas. The results show that the airborne palynological assemblages of Lanzhouurban areas also can reflect the local vegetation characters in a certain extent.The sporopollen assemblages comparsion between urban and suburban area indifferent seasons show that the major pollen types in pollen assemblages are consistentwith the florescence of dominant plants in the local vegetation. In early spring, arbors havethe highest percentages, with Ulmus as the dominant pollen types; In late spring and earlysummer, shrubs become more important, with Ostryopsis and Rosaceae as the dominantpollentypes; In summer, autumn and winter, herbs dominante the palynologicalassemblages, with Artemisia, Chenopodiaeeae and Gramineae as the dominant pollentypes. In June, the herbs influx is the highest in the whole year in the suburb, while, thepeak of the herbs influx is September in urban areas, with Artemisia and chenopodiaceaepollens as the important types in the most periods of the year, so they should be the majorallergic pollen types in the Lanzhou area, then is Gramineae and Ulmus.The comparsion results of sporopollen influx between urban and suburban areasuggest that the pollen influx are significant lower in urban than that of in the suburb,indicating that the height of pollen traps placed can influence the pollen flux. In addition,the pollen dispersal characters there are also different between the two sample sites. Forexamples, double peak of pollen influx appear at city sample site, in late spring and earlysummer(Apr-Jun) and in late summer and early autumn (Agu-Sep months)seperately,where pollen influx is the lowest in winter. While, the annual pollen influx onlyappear one peak in late spring to early summer in suburb sample site, pollen influx is thelowest in late autumn, influx is the lowest the whole year. The special weather such as duststorm and rainy days, can influence pollen assemblages significantly. In the duststorm days,the content of herbaceous pollen increases and the arbor pollen decreases, compared with the same periods when no duststorm happened. In the rainy days, usually the arbor pollen content increases and the herbaceous content decreases. The percentage of airborne sporopollen increases in short and strong rainfall days, but decreases in continuous and moderate rainfall days.