The Characteristics Of Organic Compounds Of Lake Surface Sediment In Tibetan Plateau And Its Environmental Response

Here we choose Lake Donggi Cona in Northern Tibetan Plateau as the research object.By using gas chromatography-mass spectrometry technology,biogenic organic matters were identified in these lake surface sediments as well as soil samples and these modern plants around.N-alkanes and other compounds are detected in the lake surface sediments of Lake Donggi Cona in different regions.Based on the distribution of n-alkanes in sediments, about biological sources have detailed knowledge of organic matter.In all collected samples,we found the biological input of the high terrestrial plant.Through analysis, the contribution of aquatic plants found in some samples.And these samples sampling location were colse to the lakeshore, spa side or small puddles, also explains the biological input of aquatic plants.In this paper, the different n-alkanes indexes (CPI, ACL, Paq and C27/C31) illustrates the differences of different distribution characteristic of n-alkanes in sampling locations, reflects the characteristics and changes in the lake environment from different angles.(1)N-alkane distribution of the Donggi Cona surface sediments, n-alkanes of bimodal peaks indicate a common contribution to terrestrial higher plants and aquatic plants; prepeak of n-alkanes indicate the advantages of aquatic plants input.Comparing with the results of previous studies done,the research results are consistent.And there are three forms in the carbon-number,the advantage of C31and C29indicates the biological sources are mainly herbaceous plant;and when the carbon-number maxima is at C23, indicates the advantages of aquatic plants. Comparing with the results of previous studies done,the research results are consistent.(2) The ligneous plant collected from different regions of Donggi Cona,the n-alkanes have carbon-number maxima at C27,and the distribution characteristics of n-alkanes of the herbaceous plant have carbon-number maxima at C31,thereinto two samples of the herbaceous plant also have carbon-number maxima at C25with C31or C27with C31these double carbon-number maxima.This is quite different from the distribution characteristics of the ligneous plant. Comparative analisis of the different regions of the same plants,the carbon-number maxima distribution characteristics of the herbaceous plant is affected by the regional environmental impact is bigger, the distribution of carbon-number maxima will produce changes in the environment based on the difference.Generally, carbon-number maxima of terrestrial plants at C27, C29and C31.But in Donggi Cona carbon-number maxima at C27is less than normal part of terrestrial plants, and more than half of the peak is lower than the carbon content; n-alkanes of C33instead more, in many samples exceeded n-alkanes of C27, especially in the Saussurea haoi and Chenopodium album L. is most prominent. The reason for this situation may have the following two points. First, n-alkanes of C33may be mainly derived from algae; Second, it may indicate a strong radiation and high altitude alpine conditions to promote alkane carbon chain length of Donggi Cona terrestrial plants occurred "Forward Migration".(3)By comparing the distribution characteristics of lake sediments, surface soils and modern plants found that,in addition to the two soil samples collected from the south shore of Donggi Cona, organic matter in the process of migration and transformation has changes.The other samples taken from Donggi Cona,which collected soils,sediments and plants, distribution of n-alkanes has a good indication effect on surrounding environment. The widely distributed herbaceous plant provides a source of organic matter in soil, organic matter does not has significant changes in the migration process; aquatic plants provide a source of organic matter in lake sediment, and organic matter in the sediment has not significant changes in the migration process.