【作者】 龙雨娇；

【导师】 李红春；

【作者基本信息】 西南大学 ， 第四纪地质学， 2010， 硕士

【摘要】 一个地区植被覆盖情况不仅与区域气候变化息息相关,也与人类活动的影响密切相关。利用土壤剖面的地球化学信息获取有关气候变化的规律,能一定程度上了解岩溶地区石漠化形成和发展的过程。贵州位于全球最大的岩溶生态系统——中国西南岩溶生态系统的中心,脆弱的生态环境影响了当地经济的发展。了解贵州地区植被变化情况中的自然因素和人类施加的影响,有利于我们更好地认识区域脆弱生态系统的形成机理。本文以贵州安顺三岔河土壤剖面为主要研究对象,探讨土壤中有机碳、氮的稳定同位素以及元素地球化学特征,以碳氮同位素研究为主,揭示土壤剖面反映的晚全新世以来的植被和气候的变化情况。经过初步研究得到了一下几点结论：(1)Mg、Ca、Sr元素在土壤剖面中明显的淋溶和淀积作用反映了土壤剖面在淀积层(B层)基本没有受到外界的影响。土壤剖面中其他的元素较好的相关性,揭示各种元素的地球化学性质。土壤剖面中在距离顶部27cm处的重金属的富集点,反映了人类活动(开矿及耕作)对重金属富集与向下迁移现象的影响。(2)结合土壤剖面中不同层次元素含量的变化,我们可以根据定年结果,建立比较可靠的年龄标尺。同时考虑到碳酸盐地区土壤在形成过程中,生物会吸收古老的碳酸盐溶解而来CO2合成有机物,而古老的碳酸盐中14C活度为0,这样使得有机碳定年结果偏老,为了建立可靠的年龄标尺,我们在考虑这一影响后,大致把土壤的年龄向年轻的方向校正400y。这样土壤剖面的沉积时段大约是从现今至3300 yr BP,形成于晚全新世。(3)土壤剖面C／N比值说明了土壤中的有机物来源为陆相植物为主,土壤中的的δ13Corg指示了研究地区整个晚全新世的植被都以C3植物为主；剖面中22cm以上的δ15Norg值偏高反映了土壤上部受到了粪肥的影响,137cm以下的δ15Norg和δ13Corg值的不规律性反映了受到河流季节性涨水的影响,而这之间的δ15Norg值的范围基本反映了天然土壤的有机氮同位素特征,并且δ13Corg、δ15Norg变化趋势基本一致,说明δ13Corg、δ15Norg都来源于植被分解产生的有机物。(4)δ13Corg、δ15Norg在3300 yr BP到2400 yr BP偏轻反映了研究地区植被以C3植物为主和中全新世温暖湿润的气候特点。δ13Corg、δ15Norg从2800 yr BP到2400 yr BP之间变化显示了研究区域从全新世中期向晚全新世过渡时期,夏季风逐渐减弱,气候逐渐变得干冷。从2400 yrBP到1500 yr BP,δ13Corg和δ15Norg变重也指示了晚全新世干冷的环境。(5)1500 yr BP至今,δ13Corg和δ15Norg的逐渐迅速变重反映了人类活动和气候条件的综合影响。特别是在500 yr BP(公元1400)之后δ13Corg的偏高,是与历史上明朝云贵历史上大规模的移民活动有关,人口的大幅度增长造成对住所农田等方面的需求,从而对当地的植被造成一定的破坏。(6)土壤剖面的δ13Corg记录能够可靠的反映研究地区晚全新世的植被和气候变化情况,与织金洞750 yr BP年后的洞穴沉积物中δ13C有较好的对比,这说明了土壤剖面中δ13Corg记录反映了人类活动的影响。而与董哥洞石笋中δ13C的对比说明了气候环境和人类活动的影响在贵州中部与南部存在差异。并且在研究中,除了考虑自然因素对区域植被、生态环境的影响外,我们必须考虑人类活动对区域环境变化的影响,这样才能为综合治理岩溶地区脆弱生态系统提出建议。更多还原

【Abstract】 The vegetation coverage in Karst area can reflect the severity of karst rocky desertification and we can also understand the forming and developing process of rocky desertification in karst area. As the local vegetation coverage is closely related to the regional climate changes, the regular rules of these changes can be obtained. Guizhou is located in the center of Southwest China karst ecosystem, which is the world’s largest karst ecosystem. The fragile eco-environment restricted the local economic development. Understanding the natural factors and artificial influence in the changes of vegetation coverage in Guizhou will help us realize the mechanism of fragile ecosystems.The soil profiles of Sancha River in Anshun Guizhou are the main studying objects. We discussed their stable isotopes (δ13Corg、δ15Norg)and elemental geochemistry characteristics, in order to unveil vegetation and climate changes which are reflected by soil profile in the late Holocene. Then, we come up with the following conclusions:(1)The leaching and deposition of Mg, Ca, Sr in the soil profile clearly reflected that the deposition layer (B layer) has not been influenced on the whole. The correlation of other elements in the soil profiles reflects the geochemical characteristics of various elements. This outstanding peak of high concentrations at a distance of 27cm from the top probably reflects a event caused by human activity and transfer of heavy metals in the area.(2)Considering element changes in different levels of soil profiles, we can use dating results to establish a more reliable time scale. During the formation process of soil carbonates, organism would absorb CO2 from old carbonate dissolution to synthesize organic substance, while the 14C activity in ancient carbonate is 0, which makes organic carbon dating results ofδ13Corg older. In order to establish a reliable time scale, and considering this influence, we pushed forward the age of the soil about 400y. Then the deposition of soil profile is approximately from Oyr BP to 3300yr BP, formed in the late Holocene.(3)The C/N ratio of soil profile illustrates the main sources of organic matter is terrestrial plant-based.δ13Corg values of the soil profile indicate that the C3 plant was the dominant vegetation during the late Holocene in the studied area. Theδ15N values of the part above the 22 cm line strongly reflect contamination of sewage fertilizer which had nitrogen isotopic enrichment, but the irregularity of theδ13Corg and 815NOrg values of the part below the 137 cm line may reflect the influence of seasonal swelling of the river. And theδ15Norg values of the part between 22 cm and 137 cm lines reflect that the soil profile is of natural soil.813Corg andδ15Norg values have similar variation trend, demonstrating thatδ13Corg andδ15Norg are all from the organic matters of decomposed plants.(4)The value ofδ13Corg and 815Norg is lighter in 3300 yr BP to 2400 yr BP, which indicates that the C3 plant was dominant vegetation during that time in studied area. Theδ13Corg andδ15Norg values from 2800 yr BP to 2400 yr BP reflect that the monsoon weakened gradually and the climate turned cold and dry, which happened during the transition time from mid-Holocene to late Holocene. The heavier values ofδ13Corg andδ15Norg from 2400 yr BP to 1500 yr BP reflect the cold and dry environment in late Holocene.(5) From 1500 yr BP to 0 yr BP, the values ofδ13Corg andδ15Norg increased gradually even faster, which reflect the dual effects of human activity and climatic conditions. Especially after 500 yr BP, the value ofδ13Corg gets much heavier because of the massive immigration in Ming dynasty in central-western Guizhou. And the greatly increasing population combined with the demands of house and farmland, led to the damage of local vegetation.(6) The record ofδ13Corg can reliably reflect the vegetation and climate changes of late Holocene in the studied area. What’s more, the good comparision with the value of theδ13C of the stalagmite records of Zhijin cave after 750 yr BP indicate the value ofδ13Corg reflects the impact of human activity. Compared with the stalagmite records of Dongge cave, the value ofδ13Corg in soil profile makes a good record of the changes in vegetation, climate and environment. The influence of human activities on the regional environmental changes must be considered, so as to give constructive advice about integrated management of karst region’s fragile eco-system.更多还原