Sediment Palynological Characteristic And Its Environmental Significance In Semi-humid And Semi-arid Regions:

According to Climate Change Report issued by IPCC in2007, the average global temperature has increased continuously in recent100years, and the trend of global warming is still upwards. Based on "Multi-mode Estimates of Global Precipitation Change Pattern", IPCC indicates that humid area will become moister, while arid areas will have much more drought. The northeast part of China belongs to the humid area of the pattern. However, the environment of northeast part of China is complex with its three distinct climatic zones, namely, the semi-arid, semi-humid and humid. The question is that whether the estimated results by IPCC could be applicable on the three climatic zones.A variety of substitute indexes are used to reflect directly the relationship between climate and vegetation as well as regional climate characteristics. Palynological samples in the lake sediment are chose as the substitute index in the thesis, in order to establish a high-resolution palynological deposition sequence to observe the development of global warming in the semi-arid and sub-humid zones. The thesis studies Erlongshan Reservoir of Heilongjiang Province and Xiariburidu Lake of Inner Mongolia Autonomous Region, which are located in the sub-humid and semi-arid zones respectively. It is measured by210Pb and137Cs isotope, sediment deposition age of Erlongshan Reservoir is1953-2009, and that of Xiariburidu Lake of Inner Mongolia Autonomous Region is1906-2005.The main results of the research are as follows:1. In the sediment of Xiariburidu Lake of Inner Mongolia Autonomous Region, it is mainly herbal-based with the representatives of Artemisia and Chenopodiaceae, and all woody palynological samples are coming from the outside, which indicates that it is a typical prairie environment.There are three palynological zones:palynological zone I is from1906to1949with a percentage content of Artemisia66%-74%and a percentage content of Chenopodiaceae17%-22%, and the ratio of Artemisia and Chenopodiaceae reaches to the peak point indicating it is a relatively moist period; palynological zone Ⅱ is from1949to1981with a Artemisia percentage60%and Chenopodiaceae percentage30%, and the ratio of Artemisia and Chenopodiaceae begins to decline, that is, the sign of a transition from humid to arid; palynological zone III is from1981to2005with Artemisia percentage52%and Chenopodiaceae percentage basically maintained at30%, the ratio of Artemisia and Chenopodiaceae becomes lower, indicating it is a period of relative drought.2. In the sediment of Erlongshan Reservoir of Heilongjiang Province, both herbaceous vegetation, represented by Artemisia and Chenopodiaceae, and woody vegetation, represented by birch oak, play an important role, which indicates that it belongs to the forest-grassland environment.There are two palynological zones:palynological zone A is from1953to1981, in which Artemisia occupies the highest percentage65%, Chenopodium is in a downward trend straight from13%to5%, and birch is in a growth trend peaked at20%, and the ratio of Artemisia and Chenopodiaceae increases to the peak point13, indicating it is a relatively humid period. Palynological zone B is from1981to2009with a percentage of Artemisia reduced to30%and9%-13%increases in the content of Chenopodiaceae. The ratio of these two is from high to low with the minimum of2. It demonstrates that this period is of relative drought.3. Based on a comparative analysis, the conclusions are proposed as:(1) The development of global warming in the20st century for the semi-arid and sub-humid areas of the northeast part of China is not completely consistent:the semi-arid area has been in a drying trend from the initial stage of the global warming; the sub-humid area becomes moister at the earlier period and turns to drought since the1980s.(2) Both the semi-arid and sub-humid areas of the northeast part of China turn to drought since the1980s, which is inconsistent with the results predicted by IPCC. The results of the study could be basic supplementary data to the "Multi-mode Estimates of Global Precipitation Change Pattern" of IPCC.