青海湖流域关键带碳水过程及其生态功能变化

Carbon and water processes are important physical and biological processes in the Critical Zone (CZ) and basic processes for terrestrial mass and energy cycle and interchange, which affects the stability and function of the CZ. Previous studies concerning carbon and water processes mainly focused on temperate area, while few works were done in the CZ of the Tibet Plateau. This research project was designed to establish a CZ observatory in the Qinghai Lake watershed along environmental gradients (alititude, precipitation and temperature) and different landscape (cold desert plant, cold meadow, shrub, grassland, sandy land and lake). The study will involve researches on multi-scales of soil pore-pedon-slope-catchment and leaf-individual plant-community-ecosystem, multi-interfaces of plant-atmosphere, root-soil, soil-atmosphere and soil-rock, and mult-interdisciplinary of soil science, hydrology, ecology and biogeochemistry. We use integrated methods including deep coring, ground-penetrating radar, resistivity imaging, isotope technique, remote sense and model simulation to investigate: (1) 3-D architecture of vegetation-soil-rock-microganism as well as carbon and water storage in the critical zone, (2) coupling between carbon and water at different scales and carbon and water budget, (3) interactions between freeze-thaw and carbon and water processes, and (4) prediction of carbon stabilization and water resource variation in CZ of the Qinghai Lake watershed. This study would be important for advancing theory and method for researches on CZ of cold region and ecohydrology.

碳水过程是地球关键带的重要生物物理过程，是地球表层物质循环与能量交换的基本过程，影响着关键带的稳定性和功能。过去的碳水研究大多集中在温带地区，而青藏高原是国际关键带碳水研究的空白区域。项目在青海湖流域的不同环境梯度（海拔、降水、气温）和景观单元（高寒荒漠、高寒草甸、亚高山灌丛、高寒草原、沙地、湖泊）建立关键带观测样地，从土壤孔隙、剖面、坡面、流域及叶片、个体、群落、生态系统等多尺度，植被—大气、根系—土壤、土壤—大气、土壤—岩石多界面开展跨土壤学、水文学、生态学、生物地球化学等多学科交叉研究，利用深钻技术、探地雷达、电阻层析成像、同位素技术、遥感和模型模拟等方法来探讨高寒区关键带植被—土壤—岩石—微生物三维空间结构与碳水储量格局、多尺度碳水耦合与收支、土壤冻融过程与碳水过程的相互作用机理，并预测未来青海湖流域关键带碳固持和水资源变化趋势，对发展寒区关键带科学与生态水文学具有重要科学意义。

碳水过程是地球关键带的重要生物物理过程，但在青藏高原以流域为单元的关键带碳水过程的系统研究很缺乏。项目在青海湖流域沿海拔梯度在高寒荒漠、高寒草甸、高寒草甸草原过渡带、高寒草原、亚高山灌丛、沙地和湖泊7个生态系统建立了关键带碳水过程与通量自动观测系统，系统研究了典型生态系统和流域尺度碳水收支规律。应用X射线计算机断层扫描（XCT）、探地雷达（GPR）和电阻层析成像仪（ERT）等先进地球物理技术定量刻画了高寒关键带植被—土壤—风化层—微生物空间结构与碳水储量格局；首次在高寒地区成功观测到土壤-风化层-岩石界面地下壤中流，提出了寒区坡面壤中流和地表径流在不同季节变异性的模式，估算了坡面—河道—湖泊碳输移通量；量化了冻融作用对土壤结构、微生物结构、水分和土壤碳释放的影响，明确了典型高寒生态系统多尺度碳水耦合过程及其差异性影响因素。项目研究发现青海湖咸水湖泊冬季可以吸收大量的二氧化碳，每年从大气中吸收的CO2为88万吨碳（-0.88 ± 0.49 Tg C yr−1），青海湖流域总碳汇年平均为596万吨碳（5.96 Tg C），其中陆地生态系统为5.20 Tg C。利用SPA、Noah-MP和ColM2023模型模拟了青海湖流域碳水过程的时空变化特征，预测了未来80年（2020-2100年）3种气候变化情景下流域碳固持与水资源变化趋势，流域碳固持和产水能力总体呈现增加趋势。该研究成果可为青海湖流域生态保护与碳中和目标提供科学依据和数据支撑。