云南阳宗海记录的近两千年以来的环境变化研究

The rational utilization of water resources and protection of ecological environmentsare key issues for future sustainable development of Yunnan Province which just experienced a multi-year megadrought. The basis of studies on water resources and ecological environments is correctly understanding climate changes and human activities for the last two thousand years. In this project, Lake Yangzong is chosen as the study area, which is near Kunming with a long history in Southwest China sensitive to monsoon climate. Modern pollen spectra in the study area will be used to understand the relationships among major pollen types, typical vegetations, climatic environments, and human activities. And used AMS14C and 210Pb-137Cs dating to establish the exact chronology. High-resolution pollen, charcoal and and elemental records from cores in Lake Yangzong will be applied to establish the sequences of vegetation succession, climatic change, and lake enviromental evolution in the past two thousand years, and then to detect decadal to centennial changes and those possible quasi-decadal to centennial oscillations in vegetation, climate, and lake environments. It is also purposed to examine the role of human activities in climatic and environmental changes, distinguish the influences of natural and human factors on climatic environmental changes during different periods for understanding suitable conditions of ecological environments sustained by what natural and human factors, and reveal the key factors of the rational utilization of water resources and protection of ecological environments. This project will provide basic data and important scientific basis for the sustainable development and ecological restoration in Yunnan.

对刚经历几年大旱的云南来讲，水资源合理利用、生态环境妥善保护是未来持续性发展的关键，而对水资源和生态环境研究的基础就是对近两千年的气候变化和人类活动对环境变化影响的正确认识。本项目将位于西南重镇昆明的阳宗海流域这一季风气候敏感区和具有悠久历史的地区为研究区，通过对研究区表土孢粉分析，明确典型植被和花粉类型与气候环境和人类活动间关系；利用AMS14C和210Pb-137Cs测年建立准确的年代序列，对阳宗海湖泊岩芯作高分辨率的孢粉、炭屑和元素等分析，建立过去两千年之年代际至百年尺度的高分辨率的植被演化史、气候变化史、湖泊环境变迁史，厘清自然与人为因素在环境变化中作用，认识人类活动对气候变化和环境演变的影响，探讨气候和环境变化中准年代际至百年周期性的规律性，了解形成适宜生态环境的自然因子和人文因素，揭示水资源合理利用和生态环境妥善保护的关键要素，为研究区可持续发展和生态环境恢复提供重要科学依据。

过去两千年是理解自然变率背景下人为强迫因子对气候变化影响的关键阶段，研究过去两千年的气候变化，不仅对揭示年际——百年尺度的全球变化驱动机制至关重要，而且对深入理解人类响应环境变化的机制意义重大。本项目基于季风敏感区的滇中阳宗海湖泊沉积物岩芯和滇南红河地区43个水体表层沉积物为研究对象，通过提取分析孢粉与炭屑等代用指标，探讨了现代花粉雨特征及其气候影响因子，在利用AMS14C和137Cs-210Pb测年建立可靠年代学的基础上，重建了阳宗海流域近13000年的植被、气候及森林火灾史，重点讨论了阳宗海流域在“中世纪暖期”和“小冰期”阶段的气候变化特征及驱动机制，并初步识别了人类活动对孢粉和炭屑组合的影响。研究获取的重要结果有：（1）春季、旱季和年降水量及七月、雨季和年均温六个气候因子是控制滇南红河地区现代花粉雨的主要气候因子，现代花粉雨可用于利用化石花粉记录的古气候定量重建；（2）过去13000年阳宗海环境演化分5个阶段，13200-11000 cal. a B.P. 气候温凉湿润，森林火灾多发；11000-8000 cal. a B.P. 气候较上阶段温暖偏干，森林火灾发生次数明显降低；8000-5000 cal. a B.P.，气温升至近13000年以来的最高值，湿度进一步降低，但森林火灾发生频率低；5000-800 cal. a B.P. 气温和湿度均明显下降，森林火灾发生频率有所增加；800 cal. a B.P. 至今人类活动影响加强，森林火灾发生频率低。（3）在阳宗海流域最近的1200年以来，气候变化经历暖干期、凉湿期、冷干期和暖干期4个阶段。公元780-1630年的暖期和1630-1950年的冷期分别对应了中世纪暖期和小冰期，在中世纪暖期气候表现出暖干特征，小冰期则主要呈现冷湿组合。（4）阳宗海花粉/炭屑记录重建的植被、气候和森林火灾史表明，在滇中地区，落叶阔叶成分易引起森林火灾，冷气候导致多发的森林火灾，冷干气候是宜森林火灾发生的气候条件。