中晚全新世以来抚仙湖沉积记录的环境变化研究

发布时间：2018-03-29 16:09

本文选题：抚仙湖　切入点：古环境　出处：《云南师范大学》2017年硕士论文

【摘要】：中晚全新世环境变化研究对预测未来环境变化意义重大。抚仙湖位于我国西南季风区内的云贵高原上,其形成年代久远,湖泊沉积连续,其沉积物是进行我国西南季风区古环境变化研究的理想素材。目前尚缺乏对抚仙湖千年尺度、高分辨率的古环境变化方面的研究。本文在建立抚仙湖沉积物年代序列的基础上,对抚仙湖沉积物的粒度、有机碳稳定同位素(δ13Corg)、总有机碳含量(TOC)和碳氮比值(C/N)等环境指标进行了详细分析。结果显示,在5000-2300 Cal yr BP阶段,抚仙湖沉积物的δ13Corg、TOC、TN和C/N指标具有相对稳定性,表明抚仙湖的有机质来源模式为陆源和内源共同来源的有机质来源模式,该阶段沉积物中不同粒径组分的构成非常稳定,分选系数和中值粒径值的大小几乎不变,湖泊沉积物的沉积速率较低,表明抚仙湖流域地表侵蚀程度不高且基本稳定;在2300-2000 Cal yr BP阶段,沉积物的δ13Corg明显偏正,TOC、TN和C/N明显减小,表明抚仙湖的有机质来源模式发生了明显的变化,沉积物的粒度特征在该阶段变化十分明显,细粒径的黏土和粗粒径的砂的百分含量在该阶段都有不同程度的增加,分选系数和中值粒径的波动变化较大,抚仙湖沉积物的沉积速率增大,表明抚仙湖流域地表侵蚀程度增加;自2000 Cal yr BP以来,抚仙湖沉积物的δ13Corg总体偏正,TOC、TN和C/N的值总体减小,表明抚仙湖沉积物有机质来源以内源有机质占优势,沉积物的各粒度组成变化较大,黏土的含量增加,砂的含量总体下降,且沉积物的沉积速率总体较高并且降低的幅度较大,表明输入抚仙湖的物质粒径差异明显,抚仙湖流域地表侵蚀严重。根据抚仙湖沉积物的以上环境指标特征重建中晚全新世以来抚仙湖流域的环境变化历史,并对5000 Cal yr BP来抚仙湖流域环境可能受到的气候变化与人类活动的影响进行探讨,主要得出以下结论:1、在5000-2300 Cal yr BP阶段,抚仙湖流域地表植被覆盖度较高,流域环境相对稳定,气候和人类活动对抚仙湖流域环境变化的影响不明显。2、在2300-2000 Cal yr BP阶段,抚仙湖流域地表植被覆盖度明显降低,抚仙湖流域环境在近300年内发生了明显变化,人类活动对流域环境的变化有一定的影响,但气候变化有可能是抚仙湖流域环境变化的主要控制因素。3、自2000 Cal yr BP以来,抚仙湖流域地表植被覆盖度较低,流域环境变化十分显著,人类活动可能对抚仙湖流域的环境变化产生了显著影响。4、中晚全新世以来抚仙湖流域的环境变化可能受到了西南季风减弱的影响,此外,抚仙湖的流域环境在各个阶段的变化还可能受到流域内不同程度的人类活动的干扰。
[Abstract]:The study of environmental changes in the middle and late Holocene is of great significance in predicting future environmental changes. Fuxian Lake is located on the Yunnan-Guizhou Plateau in the southwest monsoon region of China. The sediment is an ideal material for the study of paleoenvironmental change in southwestern monsoon region of China. At present, there is a lack of research on the Millennium scale and high resolution paleoenvironmental change of Fuxian Lake. The grain size, stable organic carbon isotope (TOC) and C / N ratio (C / N) of sediment in Fuxian Lake were analyzed in detail. The results showed that in the period of 5000-2300 Cal yr BP, the total organic carbon content (TOC) and the ratio of carbon to nitrogen (C / N) were measured. The 未 13CorgTOC TN and C / N indexes of Fuxian Lake sediments are relatively stable, which indicates that the organic matter source model of Fuxian Lake is the organic matter source model of both continental and endogenous sources, and the composition of different particle size components in the sediments is very stable at this stage. The separation coefficient and median particle size value are almost constant, and the deposition rate of lake sediment is low, which indicates that the surface erosion degree of Fuxian Lake basin is not high and stable, and the 未 13Corg of sediment is obviously skewed to TOCU, TN and C / N in 2300-2000 Cal yr BP stage. The results show that the organic matter source pattern of Fuxian Lake has changed obviously, the grain size characteristics of sediment have changed obviously in this stage, and the percent content of fine clay and coarse grain sand have increased in different degrees at this stage. The fluctuation of sorting coefficient and median particle size is great, and the sedimentation rate of Fuxian Lake sediment increases, which indicates that the surface erosion degree of Fuxian Lake basin increases, and since 2000 Cal yr BP, the values of 未 13Corg in Fuxian Lake sediment have generally decreased, and the values of TOCTN and C / N in Fuxian Lake sediment have generally decreased. The results show that the organic matter from the sediments of Fuxian Lake is dominant, the grain size composition of the sediments changes greatly, the content of clay increases, the content of sand decreases, and the sedimentation rate of sediments is higher and the extent of decrease is larger. The results show that the grain size of the material input to Fuxian Lake is obviously different, and the surface erosion of Fuxian Lake basin is serious. According to the above environmental index characteristics of Fuxian Lake sediment, the environmental change history of Fuxian Lake basin since the middle and late Holocene is reconstructed. The possible impacts of climate change and human activities on the environment of Fuxian Lake basin from 5000 Cal yr BP to Fuxian Lake were discussed. The main conclusions are as follows: 1. In the period of 5000-2300 Cal yr BP, the vegetation coverage of Fuxian Lake basin is high, and the watershed environment is relatively stable. The effects of climate and human activities on the environmental change of Fuxian Lake basin were not obvious. At the stage of 2300-2000 Cal yr BP, the vegetation coverage of Fuxian Lake basin decreased obviously, and the environment of Fuxian Lake basin changed obviously in the past 300 years. Human activities have a certain influence on the environmental change of the watershed, but climate change may be the main controlling factor of the environmental change in Fuxian Lake basin. Since 2000 Cal YrBP, the vegetation coverage of Fuxian Lake basin is low. The environmental change of Fuxian Lake basin is very significant. Human activities may have a significant impact on the environmental change of Fuxian Lake basin. The environmental change of Fuxian Lake basin may be affected by the weakening of southwest monsoon since the middle and late Holocene. The environmental changes of Fuxian Lake in each stage may also be disturbed by different human activities in the basin.
【学位授予单位】：云南师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P512.2;P534.632

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