季节性水位波动对通江湖泊內源/外源碳利用及浮游-底栖层耦合的影响

Pelagic-benthic coupling proves to be one of important energy paths for the understanding of trophic dynamics in lake food webs. Due to the influence of seasonal water-level fluctuation, wetland plants immigrate and emigrate to Yangtze-connected lakes periodically and this can modify the food web structure and function, and the mechanism of carbon utilization in Yangtze-connected lakes. However, little is known about the process of wetland plants-derived carbon utilization by aquatic consumers and its nutrient cycling. Wetland plants, serve as one of important allochthonous carbon sources in Yangtze-connected lakes, can be utilized indirectly by plankton but fed directly by zoobenthos, and ultimately transfer the nutrient and energy source to higher trophic level consumers in Yangtze-connected lakes. So, present study hypothesizes that wetland plant-derived carbon sources provide aquatic consumers with nutrient source primarily through benthic food web in Yangtze-connected lakes. Present study attempts to investigate the impacts of seasonal water-level fluctuation on the species composition, carbon utilization of fish and aquatic invertebrate in Lake Poyang, the largest Yangtze-connected lake in China, through the technique of stable isotopes and the analyses of TOC and C/N, and then ascertain the process and ecological mechanism of pelagic-benthic coupling induced by seasonal water-level fluctuation. Furthermore, we attempt to clarify the mechanism of carbon utilization in Yangtze-connected lakes and the process of energy cycling during different hydrological periods. Our ultimate goal is to provide theoretical guidance for the researches on the relationships between Yangtze River and Yangtze-connected lakes, and the establishment of ecological control countermeasures in Yangtze-connected lakes.

浮游-底栖层的耦合作用是理解湖泊食物网营养动态的重要能量路径。受季节性水位波动的影响，通江湖泊湿地植物的迁入与迁出会改变湖泊食物网的结构功能和碳源利用途径，然而水体消费者对湿地植物来源的碳利用途径及其营养循环的过程尚不清楚。湿地植物作为重要的外源性碳源被浮游生物利用是间接的，但可以直接被底栖动物摄食利用，并将营养与能量传递到高营养级的水体消费者。因此，本项目假设湿地植物来源的碳源主要通过底栖层为通江湖泊水体消费者提供营养源。拟采用稳定同位素技术与总有机碳、C/N分析相结合，研究季节性的水位波动对通江湖泊——鄱阳湖鱼类与无脊椎动物等物种组成及其碳源利用的影响，进而探讨在水位变化驱动下浮游-底栖层耦合的过程及其生态机制。通过揭示不同水文时期维系通江湖泊的碳源利用及其能量循环过程，将为研究通江湖泊的江湖关系和制定相关生态调控对策提供理论依据。

洪泛平原地区河流与湖泊之间的水文连通及其驱动的水位波动构成的复杂水文格局改善了陆地生态系统和水生态系统之间的物质循环和能量流动途径，这在维持湖泊生物多样性和生态系统稳定方面起着关键作用。然而，社会的发展需求导致世界上许多的湖泊丧失了与河流相连通的机会（被建闸管理），为了让人们意识到保持或重新恢复江-湖水文连通的迫切性，这就需要我们做出一些相关的工作。位于长江中下游南岸的鄱阳湖与长江以及其他几条大型河流常年保持连通，且近年来关于是否要在长江与鄱阳湖之间建立水闸并进行管理一直保持争议。本研究中，我们利用稳定同位素技术系统地评估了水文连通性及其引起的季节性水位波动对鄱阳湖基础食物资源可利用性、食物网结构、消费者的营养位置以及内源/外源碳利用的影响。结果表明，水位波动维持了鄱阳湖的食物网动态稳定性。季节性的水位波动阻碍了内源性水生植被和藻类资源的生产，增加了水生消费者直接利用外来碳尤其是来自水陆交错带滋生的碳三植物；消费者对外源碳的绝对依赖性源于水文连通和水位波动决定的栖息地多样性和资源可利用性。水生消费者的营养位置（TPs）在枯水期普遍高于丰水期。总体上，两个水文季节消费者群落所占据的营养生态位差异不显著，但各摄食功能群落尤其是肉食性鱼类的营养生态位差异较大。这些结果表明，水位波动塑造的外源碳在支持水生食物网中比内源碳更重要，因而确保湖泊与河流之间的水文连通性对维持大型通江湖泊食物网的稳定性具有重要意义。