全新世典型区域稻作土地利用与CH4排放研究-以江浙地区为例

The abnormal increase of atmospheric CH4 concentration during the middle and late Holocene is always in debate in the scientific community. In order to reveal the respective impact on the changes of CH4 concentration imposed by natural and human induced processes, one of the most important keys is to make quantitative estimation of the CH4 emission by rice agriculture (human induced wetland). In combination of geologic, archaeological, historic records and modeling methods, the research aims to establish the systematic approach to quantitatively estimating the CH4 emission and apply it to a representative region of early rice agriculture in China, Jiangsu and Zhejiang provinces. In comparison with the emission of CH4 induced by regional rice land use and natural wetland evolution, the respective contribution made by human induced and natural processes could be revealed, and the corresponding roles played in the abnormal change of Holocene CH4 concentration could be potentially discussed. The improvement of the research is the achievements of quantitative reconstructions of temporal and spatial patterns of land use, vegetation and climatic variables with high resolution during the Holocene, based on the environmental and human activity records and models. The realistic Holocene scenario is used as the boundary input for DNDC model for the past CH4 emission simulation, which could well support the accuracy of simulation. The results would offer the reference for understanding the mechanism of Holocene atmospheric CH4 concentration changes, and developing the land use strategies to tackling the greenhouse gases increases and climate changes in the future.

全新世中后期大气甲烷(CH4)浓度异常升高的原因一直在学术界存在争议，为了有效揭示自然演化和人类活动影响各自的贡献，定量重建人工湿地-稻作土地利用导致的CH4排放是解决该争议的关键之一。本研究从地质、考古和历史学证据出发，借助于数值模拟方法，在建立区域CH4排放定量重建新思路的基础上，估算我国稻作农业代表性区域-江浙地区全新世人类稻作土地利用导致的CH4排放，并对比区域自然湿地演化的贡献，探讨自然与人为过程在全新世大气CH4浓度异常增加中可能发挥的作用。本研究的进步之处在于结合记录与模拟，实现了区域高分辨率古土地利用、古植被和古气候要素时空变化定量重建，为DNDC过程模型的应用提供了更为真实的模拟场景，保证了古CH4排放估算的精度。该研究将为明确全新世大气CH4演化机制，应对未来温室气体变化制定土地利用相关战略提供参照。

陆地生态系统碳库作为全球碳循环重要的组成部分，对气候变化和人类活动影响的响应最为迅速，是未来实现“碳中和”目标的重要一环，因此理解与评估其源汇功能十分必要。CH4是导致温室效应的主要气体，全新世陆地生态系统演化对其浓度变化的影响一直在学术界存在争议。本项目从具有悠久人类活动历史的江浙和安徽地区入手，通过地质、考古、文献记录和数值模拟相结合的方法，在定量化重建区域全新世古植被、古气候、古泥炭地和古稻作土地利用时空格局的基础上，利用区域化改造的温室气体模型，尝试模拟了自然和人类活动影响情境下的区域陆地生态系统CH4排放量变化。结果显示：全新世期间，江浙和安徽地区泥炭地规模整体变化不大，约为1500km2。空间上主要集中分布在沿海地区和区域北部江淮地区。同期稻作土地利用呈现了持续增加的趋势（206km2-14693km2），空间扩张过程主要围绕北部和南部两个人类活动中心，且稻作土地利用集中区域的周边往往分布着丰富泥炭地。全新世期间，泥炭地的发育导致的CH4年均排放量约为0.12-0.13Tg/yr，而稻作土地利用区域的CH4年排放量从0.01Tg/yr逐步增加至0.47Tg/yr。因此，全新世早中期自然过程对大气CH4浓度变化的贡献大于人为过程，但6kaBP之后，人为过程对区域CH4排放的贡献超过了自然过程。项目在实施过程中积累了大量古泥炭地和古人类活动基础数据，包括60余个泥炭地和孢粉剖面信息，2800余个考古遗址点位信息等。上述结果和数据将为理解全新世大气CH4浓度变化机制、评价未来陆地生态系统CH4排放趋势提供参照。