应用沉积物枝角类稳定同位素信号评价富营养化对湖泊有机碳源的长期影响

With long-term catchment development, lakes in Yunnan have increasingly experienced nutrient enrichment and cynobacteria blooms, with significant ecological consequences such as changes in food web structure and organic carbon cycling. To uncover the effect of eutrophication on organic carbon sources and trophic pathways, we focus on cladocerans and their planktonic and benthic carbon sources and identify the signals of organic carbon source and the compositional change of sediment organic matters through stable isotope methods. Focusing on four lakes of different trophic state, spatial and seasonal surveys will be conducted on live cladocerans and their main carbon sources (i.e. phytoplankton and macrophytes) in lake waters for quantifying the relative role of benthic and planktonic pathways in driving the change of cladoceran isotope signals and identifying the drivers for their spatio-temporal variations. Through combining modern processes with surface sediment surveys, the reliability and sensitivity of their representation for modern isotope indicators will further be assessed. With time series analysis of the isotopic signals of both cladoceran valves and sediment organic matters, the history and patterns in the compositional changes of sediment organic matters and the pathways of carbon transfer during the last century were identified through the application of isotopic mixing models and multi-proxy sediment analyses. Finally, the regional patterns and processes in the transfer pathways of organic carbon will be evaluated in the context of nutrient enrichment. Therefore, this study will serve as scientific basis for evaluating the processes behind organic carbon cycling and facilitate the ecological restoration for polluted lakes in Yunnan.

持续的流域开发导致了云南湖泊面临富营养化、蓝藻爆发等环境问题，也改变了食物网结构与有机碳循环模式。为了评价富营养化过程对湖泊内源有机碳源及其传输路径的影响，拟针对枝角类浮游与底栖碳源开展综合研究，应用碳稳定同位素方法示踪有机碳源信号与沉积物有机质组成的变化。以营养水平不同的四个湖泊为研究对象，对现生枝角类及其主要碳源（如浮游植物、有机碎屑）开展季节与空间调查，识别枝角类的稳定同位素信号对浮游与底栖碳源的指示意义及其时空变化的主控因子。结合现代调查与表层沉积物分析，辨识枝角类壳体同位素信号指示现代过程的可靠性。进一步通过钻孔枝角类壳体与总有机质碳同位素信号的时间序列分析，应用同位素混合模型与多指标记录，甄别近百年来沉积物有机质组成与有机碳来源变化的历史与特征，最终识别高原湖泊营养盐富集影响有机碳传输路径的长期过程与区域模式。本研究可为认识污染湖泊的有机碳循环过程及开展生态修复提供科学依据。

持续的流域开发导致了云南湖泊面临富营养化、蓝藻爆发等环境问题，也改变了食物网结构与有机碳循环模式。为了评价富营养化过程对湖泊有机碳源及其传输路径的影响机制，项目围绕枝角类等生物指标对浮游与底栖碳源开展综合研究和对比分析，重点应用稳定同位素方法示踪有机碳来源的变化特征与长期模式。首先以营养水平不同的14个云南湖泊为研究对象，对现生浮游动物（枝角类等）及其主要碳源（如浮游植物、沉水植物）开展了空间与季节调查，发现有机碳源及其传输途径是导致生物体碳同位素信号差异的关键过程。在空间分布上，湖泊生物碳同位素信号受到水温、水深等因素的明显影响。季节变化上，较高的生物碳同位素信号在深水湖泊中与生长速率较高、可溶性无机碳源利用增多等过程有关，而在浅水湖泊中主要受雨季流域输入增强、陆源有机质占比增加有关。结合现代调查与表层沉积物分析，进一步明确了枝角类的稳定同位素信号指示浮游碳源的可靠性及其主控因子，并识别出生物群落结构与有机碳传输通道上存在明确的水深阈值（8-10米）；而在浅水湖泊中，该指标对底栖碳源的示踪受外源输入、浮游碳源传输等过程影响，同时枝角类群落中底栖物种大量降低，均导致了壳体同位素信号示踪底栖碳源的可靠性显著降低。通过8个湖泊钻孔的多指标记录，提取了生物残体与有机质碳同位素信号的时间序列，应用同位素混合模型等定量识别了湖泊营养盐富集增强有机碳源浮游路径传输的长期过程，判别了区域模式上流域外源输入、水位波动等过程对湖泊有机碳传输和稳定同位素信号的驱动效应。本研究的开展可为污染湖泊的有机碳循环过程识别并开展生态修复提供科学依据，同时为流域碳汇估算和湖泊碳源评估提供了技术支撑。项目共获得关键数据14800个，已发表SCI论文6篇(含TOP期刊论文3篇)、EI论文8篇、核心等中文期刊论文10篇，第一标注论文5篇；培养毕业研究生16人、博士后1人，核心成员新增主持国家自科基金资助5项。