海平面上升对盐沼湿地碳库要素稳定性与固碳效率的影响及预测

The coastal salt marshes are identified as the “Blue Carbon”. However due to global climate change, the expected sea-level rise might lead to the multiple-factor hydrological stresses including tidal range change, prolonged inundation and saltwater intrusion in the coastal ecosystems. As a result, the changed hydrological environment might aggravate the destabilization of carbon cycling processes and influence the constancy of carbon sequestration capacity in the coastal salt marshes.. The natural properties of salt marsh vegetation, hydrological conditions and mudflat geomorphology, make the Yangtze Estuary an ideal area for the studies on impacts of environmental change. In order to simulate the changed hydrological conditions in terms of sea-level rise scenarios, a pair of multiple-factor experiments will be conducted in the natural tidal mudflat (with natural tide currents) and the independently developed loop-type flumes (with simulated hydrological conditions), with the mesocosms (vegetation-soil monoliths of dominant Poaceae and Cyperaceae communities) from the salt marshes.. This project will integrate the multi-objective techniques of eco-geomorphologic and biogeochemical research, including the structural stability (erosion or sediment accretion) of vegetation-soil system, CO2 and CH4 emission, plant photosynthesis and assimilated carbon allocation, carbon utilization by soil microorganisms, and export of particulate and dissolved carbon in water. Thereafter, a processes-based carbon cycle model embedding hydrological regimes will be developed, based on the influence mechanism of sea-level rise on the constancy of key carbon pools (vegetation, sediment, soil microorganism and water) and the consequent carbon sequestration for the salt marshes. . The aims of this study are (1) to investigate the coupled responses of structural stability of key carbon pools and carbon process components to sea-level rise treatments, and (2) to predict the spatial-temporal dynamics of carbon sequestration efficiency of the salt marshes in the Yangtze Estuary under sea-level rise scenarios. The key question needed to be considered is whether there will be a shift between carbon "sink" and "source" in the coastal salt marshes in East China under sea-level rise? Through this study, the research team purposes to put forward the scientific support for the adaptive maintenance strategy of carbon sequestration capacity of the coastal ecosystems in China.

海平面上升可能引起潮差变化、淹水胁迫和盐水入侵等协同效应，这使得海岸带盐沼湿地碳循环过程和碳封存功能处于不稳定的状态。本研究拟在长江口盐沼湿地潮滩和自制双向环型水槽模拟多因子的海平面上升情景，建立湿地关键碳库要素－优势盐沼植被与土壤（含土壤微生物和水体）实验系统，观测禾本科和莎草科植被－土壤系统的结构稳定性（侵蚀或泥沙淤积），以及系统CO2与CH4排放、植物光合固碳与分配、土壤微生物生物量碳累积、水体颗粒态和溶解态碳输出等多界面碳过程的变化。进而基于湿地生态地貌和碳过程的水文调控特征，构建盐沼湿地“水文－碳过程”模型，揭示盐沼湿地关键碳库要素结构稳定性及多组分碳过程对海平面上升效应的耦合响应机理，并预测海平面上升情景下长江口盐沼湿地固碳效率的时空格局变化。拟回答的关键科学问题为海平面上升条件下盐沼湿地是否会发生碳“汇－源”的转换？本研究希望为我国海岸带生态系统碳汇的适应性管理提供科学依据。

滨海盐沼湿地被称为蓝碳生态系统，具有很高的“碳汇”功能。然而，滨海湿地位于海陆交界地带，极易受到全球变化的影响，尤其是加剧的海平面上升。本研究以长江口盐沼湿地为对象，研究在未来海平面上升情景下，水-盐多因子的交互作用对盐沼湿地多组分碳过程的影响，并结合野外涡度协方差通量观测方法，探究海平面上升情景下盐沼湿地净生态系统碳交换量的变化及原因。此外，本研究还综合应用人工环境控制实验、野外观测、遥感影像解译、阈值分析和模型模拟等多种研究方法，探究长江口典型盐沼植物被的环境适应性和生物-地貌相互作用机制，拓展生物-地貌耦合模型在盐沼植被修复策略中的应用。基于本项目已发表/接收论文19篇，其中SCI论文16篇，授权专利3项，在国内学术会议上做了分会场报告2次。本研究主要的学术成果包括，（1）盐沼植物光合过程较呼吸过程对淹水和盐度处理的响应更敏感。淹水和盐度均会抑制湿地土壤呼吸，但曝气会导致土壤呼吸激增，而削弱盐度对土壤呼吸的抑制作用；（2）盐沼植物-土壤系统植被光合固碳能力受水盐因子的抑制程度高于对碳排放能力的抑制，导致净生态系统碳交换量降低；（3）未来海平面上升背景下，淹水和盐度条件的改变会抑制盐沼植物的光合固碳能力、盐沼地上植物呼吸和土壤呼吸。水盐条件的改变对植物光合固碳能力的抑制是导致盐沼净CO2吸收能力降低的主要原因；（4）滨海湿地的土地利用变化通过改变各土地类型的水文条件、植被生长、土壤理化性质和土壤中微生物活动等环境条件，造成土壤碳、氮储量以及生态系统碳和氮储量显著减少，从而促进了CO2、CH4和N2O排放和增强了温室效应；（5）对长江口盐沼模型（Salt Marsh Model for Yangtze Estuary, SMM-YE）进行了结构优化与参数完善。在模型中结合了生物过程与非生物过程之间的相互作用，较好地描述了植被生长和横向扩张、沉积动力学和高程变化的年际变化。生态过程模型在盐沼前沿植被修复和滨海湿地外来物种入侵风险管理方面具有巨大的应用潜力。