【作者】 谭志海；

【导师】 黄春长；

【作者基本信息】 陕西师范大学 ， 自然地理， 2004， 硕士

【摘要】 全新世生态环境演变是一个复杂的过程，受多种因素制约，只有通过多种气候替代指标综合分析，才有助于科学地恢复全新世生态环境演变的过程。磁化率、TOC反映气候干冷、温湿的变化；木炭屑反映野火发生的强度、频率，进而反映全新世气候的干-湿、冷-暖变化。我们清楚认识到，作为生态环境干扰因素之一野火，在气候变化背景下，成为驱动渭河流域生态环境演化的一个直接因素，随着人类活动范围的扩大，人为火促成的野火活动已成为加速全新世生态环境演化的一个重要因素，因此，研究野火活动及人类活动与生态环境演化关系，对了解和认识全新世生态环境演化具有重要意义。 渭河流域是华夏文明的发祥地之一，史前时期相继发展了大地湾文化、仰韶文化、龙山文化、夏商文化、先周文化、寺洼文化等，它是人类最早进行农牧业活动的一个重要区域。随着人口增长，人类长期砍伐、焚毁林木、开垦土地等活动的范围逐渐扩大，人们通过使用火促成的野火活动更加频繁，进而影响着全新世生态环境演化过程。本研究通过多种手段探讨全新世野火活动及人类活动与生态环境演变的关系。 本研究通过大量野外考察选取了渭河流域北至南方向上三个全新世黄土-土壤剖面。三个剖面地层稳定，发育连续完整，保存良好，具有典型性，分别对三个剖面进行高密度采样，并对剖面样品分别进行磁化率、TOC、木炭屑室内分析和测定，其中通过对野火活动记录最理想的代用指标木炭屑统计和鉴定，结合生态环境的替代指标磁化率、TOC分析和测定来试图讨论野火活动的历史，对生态景观的影响，气候的变化以及人为火促成的野火活动对生态环境的干扰等，来进一步说明野火活动与生态环境演变的关系，对了解渭河流域全新世生态环境演变具有重要意义。同时，分析人类活动与生态环境相互作用及人地关系演变进程。其研究成果为： (1)通过木炭屑、TOC、磁化率、历史文献等多项指标结果分析渭河流域全新世环境变化：在马兰黄土堆积时期，在总体较冷、干的背景下(相对全新世而言)，更多地显示了波动性，此时粉尘堆积过程显著，生物成壤作用微弱，呈现半荒漠草原环境；全新世早期(11，500～8，500 a B．P)处于从干冷向温湿转变的一个渐变过程，与马兰黄土堆积时期相似，气候干旱而不稳定；全新世中期(8，500～3，100a B.P)全新世以来最温湿的时期，植被茂盛，古土壤发育强烈，有机质积累丰富，但此时期并不是持续的温暖湿润期，存在着一个气候恶化阶段。全新世晚期(3，100a B.P~0)又一次相对干早的阶段，风尘堆积加速，生物化学成壤作用减弱，生物有机量大幅度降低。3，100 a B.P后在黄土层与、表土层(TS)木炭屑数量又大幅度上升，达到峰值，可能因历史时期人类活动的扩大产生大量的木炭屑，同时使得土壤环境进一步退化，加重气候干早程度。 (2)通过木炭屑、Toc、磁化率、历史文献等多项指标结果分析木炭屑记录与总有机碳(Toc)的关系。作为生态环境变化的替代指标总有机碳(Toc)和木炭屑往往在土层中相伴而生，它们对生态环境指示作用范围既有联系，又有区别;总有机碳(Toc)实质上包含了生物成壤作用形成的腐殖质中有机碳的含量和野火形成的木炭屑有机碳的成分，它是无定形碳，它主要反映土坡有机质积累状况，TOC含量的高低与气候变化和植被覆盖度变化呈现正相关;而木炭屑具有形状的木质结构，外形边缘清楚可见，在显微镜下能够清楚辨认，，通过木炭屑浓度变化定量分析并可以恢复地质历史中野火发生的频率、强度及其动态演化过程。可见，总有机碳(Toc)并不能完全指示生态环境中野火活动;而木炭屑才是直接指示野火活动。 (3)通过木炭屑、Toc、磁化率、历史文献等多项指标结果分析野火的发生与环境变化关系。末次冰期马兰黄土堆积时期(15，oooa B.P一11，500 a B.P)呈现半荒漠草原生态环境，气候寒冷干旱，区域性和当地性野火常有发生;全新世早期(11，50oa B.P~8，500a.B.P)本时期处于从干冷向温湿过渡阶段，此时与马兰黄土堆积时期相似，野火活动频繁发生;全新世中期(8，500一3，100 a B.P)，全新世最为温湿的时期，植被茂盛，古土壤发育强烈，呈现森林和森林草原景观，此时本地似乎野火活动极少发生，但是，大量细粒木炭屑出现则指示源区远源成分较大，与区域范围的沙尘同源，不排除渭河流域个别地方可能有野火发生，与人类放火毁林，开垦土地，种植农作物的结果。标志着渭河流域的自然景观开始逐步被人工景观所替代:全新世晚期(3，100 a B.P~0)，成为全新世又一个相对干早的阶段，生物化学成壤作用减弱，木炭屑浓度大幅度增加，野火活动频繁发生，特别是3，IOOaB.只随着人类活动范围扩大，放火毁林、开垦土地等活动频繁发生，导致木炭屑大量出现，渭河流域正在由自然景观向半自然、半人工景观过渡。1500aB.P以后，前半期木炭屑浓度大大减少，可能是荒地开垦殆尽，几乎呈现为农田人工景观，而后半期大颗粒木炭屑浓度增加了，可能由于近代人口增长，人们生活用火和垃圾增加的结果。 本研究特色与创新点在于通过沉积物中木炭屑记录，来反映野火活动与全新世生态环境动态演?更多还原

【Abstract】 Ecological environment in Holoeene is so complicated a phase that it derived from a variety of factors. Only through various climatic proxy for synthetic analysis can we contribute to the recovery of Ecological environment variation in Holoeene .The magnetic susceptibility. Total organic carbon (TOC) indicate a drier and colder , warmer and wetter climate, while charcoal indicates intensity, frequency of Wildfire activity. Under the circumstances of climatic changes, Wildfire is not the only factor interfering the ecological environment, but a direct factor caused great changes of ecological environment in Weihe river drainage. With the enlargement of human scope of activities, Wildfire activity has already become and accelerated the transformation of the ecological environment. So, it is well worth studying the relationship between Wildfire activity, human activity and even the shift of ecological environment .It is significant for us to acknowledge those in ecological environment.It is one of the Chinese cultures which originated from Weihe river drainage, gradually with the development of Dadiwan culture, Yangshao culture, the Longshan culture, Xia and Sang dynasty culture, etc. It is an important area where the human beings first carried on the activity of farming and stockbreeding. With the rapid growth of population, innovation of tools, hunting and gathering, especially the enlargement of many years of farming, human became stronger by interfering and influencing ecological environment with the purpose of improving their own lives. The author attempts to focus on the relationship between Wildfire activity, human activity and the changes of ecological environment during Holoeene. . The main findings are:(1) Change of environment during Holoeene in Weihe river drainage were studied by proxy climate data of magnetic susceptibility, total organic carbon and charcoal: Piled up period in the Malian loess, it is the most typical deposit of Aeolian dust accumulated in the semi-desert environment. An early Holoeene (11, 500~8, 500 a B. P) was much similar to Malian loess, arid but unstable. During the Holoeene "climate optimum"(8,500~3,100 a B.P), it was wetter and warmer, and then was active bio-pedogenic processes during thetime of soil formation, while it was not a continuous warm-humid period. During the late Holocene (3, 100 a B.P~0), it was weak bio-pedogenic processes during the time, which became another relatively arid stage during Holocene. From3, 100a.B.P on, with the increase of human activity, Bio-pedogenic processes during the time of soil formation subsided. In the past 1500 years, mankind has reduced the interference of the region soil -vegetation system for a period of time. This may have already totally cultivated the farmland, with the growth of population, employment of fire and production of trash, and further deterioration of farmland by human.(2) The relationship with charcoal records and total organ carbon by proxy climate data of magnetic susceptibility, total organic carbon and charcoal: As the climatic proxy of total organic carbon and charcoal often exist together in the soil layer, which are linked with the ecological environment, there is a complete difference. Total organic carbon (TOC) includes the organic carbon in bio-pedogenic processes during the time of soil formation and the organic carbon of charcoal in Wildfire .It has irregular form and reflects organic accumulation of soil, while the charcoal is a wooden structure, which can be seen and recognized clearly through microscope, and can reflect objectively that of the Wildfire. It is obvious that total organic carbon (TOC) cannot point out the Wildfire activity in the ecological environment completely and the charcoal point out the Wildfire activity directly.(3) The relationship with Wildfire activity and environmental changes by proxy climate data of magnetic susceptibility, total organic carbon and charcoal: Piled up period in the Ma-Ian loess (15,000a B. P~ 11, 500 a B. P), the climate is arid, on semi-desert grass更多还原