黄河三角洲咸淡水交汇区水文连通变化对盐地碱蓬群落的影响机理

Targeting the strategic demands of the development of the Ecological Economic Zone of the Yellow River Delta and academic frontiers, our goals are to elucidate the impact mechanisms of altered hydrological connectivity (HC), subject to human activities and climate change, on the distribution patterns of S. salsa in mixing zones of fresh and saline water of the river delta. This study is to quantify hydrological connectivity to understand how external drivers influence structural, functional and processes connectivity across space and time, thereby revealing multiscale nature of strength, direction, and significance of external forcing. Combining field surveys and controlled experiments at various sites located along a gradient from the sea to the land at tidal flats and within the tidal creeks, we characterize the pattern change of brackish areas and establish the relationships between changes of structural, functional and process connectivity of HC, and seed availability and germination, seedling establishment and plant traits. Our results aim to reveal the impact mechanisms and thresholds of HC alterations on saltmarsh vegetation at different stages of their life history. Using graph- and information theory-based approaches, we build the networks of structural, functional and process connectivity for HC. We assess the synergy, uniqueness, and redundancy in interacting environmental variables as nodes and links of the HC networks. To elucidate the interrelationships of multiple variables at multi-scales, we develop a general framework for transport on multiscale coupled connectivity systems, through multilayer networks interacting through interlayer links. This study will help inform managers to better understand the trade-offs between engineering development and coastal wetlands conservation, as well as to provide tools and theory for conducting hydrological connectivity-based restoration of coastal saltmarsh vegetation. This work also contributes to more holistic characterizations of system behavior, and furthers our understanding of complex ecohydrological interactions, and benefits the disciplinary development of eco-hydraulics.

面向黄河三角洲生态经济区发展战略需求和学术前沿，针对上下游重大人类活动和气候变化驱动下，三角洲湿地咸淡水交汇区水文连通变化，揭示不同水文连通类型格局变化对盐地碱蓬群落分布格局的影响机理。通过选取由海向陆潮滩及潮沟区域，结合现场调查和控制实验，研究咸淡水交汇区时空格局变化特征，建立水文结构、功能和过程连通变化与盐地碱蓬种子可利用量、种子萌发、幼苗定植以及成体植株性状特征之间的关系，揭示水文连通变化对不同生活史阶段盐沼植被的影响机理及阈值。基于图论和信息论，构建咸淡水交互区水文结构、功能和过程连通网络，识别网络中冗余性、唯一性和协同性节点和边，构建耦合结构、功能和过程的水文连通网络模型，阐明各连通类型之间的相互转化规律。研究将为黄河三角洲管理者权衡水利工程开发、管理和湿地保护之间的关系，开展基于水文连通调控的滨海湿地盐沼植被修复提供理论和方法学支撑，为我国生态水利基础科学理论发展做出贡献。

由于人类活动的影响，黄河三角洲滨海湿地生态系统遭到了干扰和破坏。盐地碱蓬是滨海盐碱湿地的先锋物种，具有较大的生态价值和经济效益。为了深入研究黄河三角洲滨海湿地生态系统的功能结构和水文连通对盐地碱蓬生活习性的影响，本项目基于现场调查、室内实验、野外实验和数据建模等多种研究手段，结合课题组多年数据积累，经过近3年的研究，得到的成果如下：①基于PCA降维方法提出了水文连通强度指数的新模式，分析了水文连通强度对盐地碱蓬密度、生物量和表型特征的影响；②基于随机森林算法构建了滨海湿地土壤盐度反演模型，分析了黄河三角洲滨海湿地表层土壤盐度的时空分布变化情况；③构建了咸淡水交汇强度指数，分析了黄河三角洲咸淡水交汇强度的时空分布，揭示了土壤盐度对盐地碱蓬不同生活史阶段的影响；④发现了滨海湿地内地理空间自组织泥沼裂缝对盐沼碱蓬和生态系统稳定性的促进作用；⑤得到了斑块大小的稳定性阈值（20 m2），阐明了斑块边缘贝壳聚集对盐沼斑块的积极影响和斑块内部贝壳聚集对盐沼斑块的消极影响；⑥研究了人类活动对贫营养状态下自然海草生态系统的影响，肯定了完整食物网对外部压力更强的抵抗作用。本研究为黄河三角洲基于水文连通调控的滨海湿地盐沼植被修复提供了理论支撑，部分成果已应用到黄河三角洲滨海湿地盐地碱蓬修复示范工程，取得了较好效果。