石羊河流域千年尺度有机碳库变化及其影响机制

A fully comprehensive and credible explanation of soil organic carbon cycle - climate feedback process and mechanism can be achieved only when regional millennial scale organic carbon sink and its influence mechanism studies are conducted. The inland river basin is the most intense area of human activity in arid and semi-arid regions, and is the key area of China's silk road economic belt. However, the millennial scale carbon sinks in inland river basins are still lacking insight into the mechanism of the carbon balance, and the actual magnitude of the carbon sinks remains uncertain. This study proposes to conduct a case study in the Shiyang River drainage basin, in arid northwest China. Based on pollen analysis and geochemistry proxy measurement of sediments samples from upstream Holocene section and surface soil of different vegetation types, modern pollen transport characteristics of the entire basin and pollen records from 8 Holocene sedimentary sections will be integrated to quantitatively reconstruct the millennial-scale changes of watershed vegetation zones by defining a new pollen-precipitation index and to illuminate the relationship between millennial scale organic carbon storage and vegetation type distribution. On this basis, a quantitative estimation model based on pollen assemblages will be built to evaluate the Holocene millennial scale organic carbon sink in the Shiyang River drainage basin. Spatial and temporal variations of the millennial scale organic carbon sink in the Shiyang River drainage basin will be analyzed to quantify the contribution rate of the impact from natural factors and human activities to the changes of the millennium scale organic carbon sink, and further clarify the influence mechanism of millennial scale organic carbon sink in the Shiyang River drainage basin. This research will provide scientific bases for estimating the response mechanism of regional organic carbon cycle in future climate change circumstances.

对区域过去千年尺度碳汇连续演化规律的研究，是理解全球变化背景下土壤有机碳循环-气候反馈过程和机制的基础。内陆河流域是干旱半干旱地区人类活动最为剧烈的区域，同时也是我国生态环境建设和丝绸之路经济带建设的重点地区，但这一地区实际碳库的大小及千年尺度演化过程尚不明确，千年尺度碳循环机制的研究还存在争议。本项研究拟选择我国西北干旱区的石羊河流域，以孢粉分析为主，综合运用地球化学指标测定、遥感分析等多种研究方法，通过分析流域全新世孢粉组合特征，明确流域千年尺度植被演化规律及千年尺度有机碳库与不同植被带关系；在此基础上构建基于孢粉的流域千年尺度有机碳库定量估算模型，定量估算石羊河流域千年尺度有机碳库；进一步分析石羊河流域全新世千年尺度有机碳库时空变化特征，明确千年尺度有机碳循环的关键影响因子，阐明石羊河流域全新世千年尺度有机碳循环影响机制，为评价未来气候变化条件下区域有机碳库响应特征提供科学基础。

本项研究选择我国西北干旱区的石羊河流域，旨在明确流域千年尺度有机碳库与不同植被带关系；构建基于孢粉的流域千年尺度有机碳库定量估算模型，明确石羊河流域全新世千年尺度有机碳库时空变化特征；确定流域千年尺度有机碳循环的关键影响因子，阐明石羊河流域全新世千年尺度有机碳循环影响机制，为评价未来气候变化条件下区域有机碳库响应特征提供科学基础。利用孢粉数据重建流域全新世千年尺度植被变化，结合现代植被有机碳库与不同植被带关系，计算得到石羊河流域早、中、晚全新世年代际固碳量分别为5.37 Tg C、5.20 Tg C和3.55 Tg C，对应的流域植被固碳能力分别为128.99 g C m-2 yr-1，124.93 g C m-2 yr-1和85.44 g C m-2 yr-1。与此同时，集成全流域沉积信息建立全新世年代框架，计算全新世早、中、晚期石羊河流域上、中、下游沉积物沉积速率，结合剖面TOC数据，进一步利用蒙特卡洛模拟方法，得出石羊河流域千年有机汇碳能力早全新世为3.51 Pg，平均沉积速率24.10±0.043 g C m-2 yr-1；中全新世为3.94 Pg，平均沉积速率27.03±0.045 g C m-2 yr-1；晚全新世为2.61 Pg，平均沉积速率17.95±0.033 g C m-2 yr-1。由此可知，石羊河流域全新世千年时间尺度碳汇能力为同期年代际尺度的18.69%—21.61%，尽管流域不同时间尺度有机碳汇能力均对气候变化表现出相似的响应机制，但内陆河流域长时间尺度有机汇碳能力仍可能被严重高估。