湖泊草藻型稳态转换下陆源有机质对水生食物网的碳源贡献变化及其机制

Regime shift between macrophyte and phytoplankton is one of the main environment problems in shallow lakes. Although aquatic ecosystems typically receive significant inputs of terrestrial organic matter, the contribution of terrestrial support to lake food webs under a change of alternative states has not yet been adequately traced and quantified. In this proposed study, we will select typical macrophyte and phytoplankton dominated lakes in northern grassland areas for field experiment to examine the role of terrestrial inputs in food webs. We will first use stable isotopes to analyze the composition of terrestrial organic carbon from the river inflows and try to identify its relation with terrestrial vegetation. Then, a Bayesian stable isotope mixing model will be used to estimate the relative contribution of terrestrial carbon source to higher trophic levels under different lake regimes. Environmental factors and biological resources structure will be also analyzed in the study region throughout the year and their interactions with the variation of contributions of terrestrial organic matter will be demonstrated. Furthermore, combined methods including fatty acid biomarkers and in situ stable isotope labeling experiment will be applied to identify the main food sources and trophic positions of aquatic organisms such as invertebrates and fish. Based on this, we characterize the feeding relationships between the components of the system and diagram the food web structures of macrophyte and phytoplankton dominated lakes, which describing the carbon flow originating from terrestrial vegetation to predators of the upper trophic levels. Taken together, we want to uncover the effects of the shift of alternative states on the contribution of terrestrial organic matter to aquatic food webs and its mechanisms in lakes. The results of this project will contribute to the theory of aquatic food web ecology, and provide the scientific supports for the ecological restoration of eutrophic lakes.

湖泊草藻型稳态转换是我国浅水湖泊面临的主要环境问题之一，陆源有机质输入作为维持湖泊生态系统食物网的重要能量来源，其在湖泊稳态转换过程中对水生食物网的碳源贡献变化及其机制一直未深入研究。本项目拟以我国北方草原地区典型草型和藻型湖泊为研究对象，首先利用稳定同位素技术辨析入湖陆源有机质的来源组成及与陆生植物的潜在关系；其次利用同位素混合模型定量比较陆源有机质在不同稳定态湖泊中的碳源贡献差异，并探讨促成陆源有机碳贡献发生时空变化的关键环境驱动因子；然后结合脂肪酸标志物技术与稳定同位素标记原位示踪试验，判断无脊椎动物和鱼类等消费者的主要食物来源与营养关系，并通过构建食物网结构模型阐明陆生植物等初级生产者碳源沿食物链的能流传递途径；最后综合上述研究试图揭示陆源有机质在不同稳态湖泊生态系统食物网中的能流途径变化及其响应机理。研究结果将丰富湖泊食物网生态学理论，并为富营养化水体修复提供科学依据。

湖泊草藻型稳态转换是我国浅水湖泊面临的主要环境问题之一，而陆源有机质输入在湖泊稳态转换过程中对水生食物网的碳源贡献变化及其机制一直未深入研究。本项目以我国北方草原地区典型草型湖泊乌兰泡和藻型湖泊呼伦湖作为研究对象，首先利用稳定同位素技术辨析入湖陆源有机质的来源组成及与陆生植物的潜在关系，结果显示陆生植物是入湖颗粒有机物的重要来源（44.3%），并且主要基础食源与消费者的δ13C比值在草型、藻型湖泊间整体表现出显著性差异，藻型湖泊食物源和消费者的δ13C比值明显低于草型湖泊。项目接着运用SIAR模型定量解析了陆源有机物等基础食源对草型、藻型状态下食物网的碳源贡献，结果表明草型、藻型湖泊中外源有机质均是大多数消费者重要的碳源，但外源有机物对消费者的碳源贡献在藻型湖泊中呈现出更高的贡献率。在此基础上，项目还同步分析了陆源有机质输入在不同稳定态湖泊中的空间与季节贡献差异，并确定了影响其贡献率变化的关键因子，其中入湖径流量、浮游植物生物量及温度等是驱动陆源有机质贡献率季节差异的主要因子，而水生植物生物量、水深及浊度是造成空间差异的主要因子。最后，项目结合脂肪酸标志物技术判断了无脊椎动物和鱼类等消费者的主要食物来源与营养关系，并通过构建食物网结构模型阐明了陆生植物等初级生产者碳源沿食物链的能流传递途径。该食物网在草型状态下包含6条主食物链，在藻型状态下包含5条主食物链，其中草型湖泊中的底层碎屑食物网途径贡献重大，而藻型湖泊中的以外源有机质为主要碳源的表层食物网途径则得到明显增强。此外，项目设计了玉米叶片作为天然标记材料的稳定同位素原位示踪试验，结果显示湖滨带结构更复杂性的水域往往存在着更高强度的陆源有机质消解过程，从而进一步解析了草藻型不同稳定态湖泊之间外源有机质贡献存在差异的机制。项目研究结果丰富了湖泊食物网生态学理论，并为富营养化水体修复提供了科学依据。

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