梯级水电开发对澜沧江鱼类功能多样性的影响及驱动机制

Eco-environmental problems caused by the development of hydropower, particularly cascade hydropower, has become an important factor restricting hydropower resources utilization in China. Among these problems, changes in fish diversity have received plenty of attention from the public, and can substantially affect the sustainability of national hydropower development. However, existing studies have focused more on the effects of dam on fish species diversity at the local scale, but less on fish functional diversity, especially at the catchment scale. It is still unclear that how cascade hydropower affects fish functional diversity, thus hinder fish resources conservation in rivers under cascade hydropower development. In this proposal, we selected the Lancang River as our study area. Data on fish composition and distribution, fish functional traits, and environmental factors before and after cascade hydropower development were firstly obtained through extensive field sampling and literature searching. Then based on the datasets, we aim to 1) reveal the effects of cascade development on fish functional diversity at the alpha and beta diversity level; 2) establish the relationship between fish functional traits and environmental factors in the past, and construct a structural equation model to clarify the mechanism of how environmental changes caused by cascade hydropower development affect fish functional diversity. The outcomes of this project will provide scientific data and theoretical support for fish resources conservation in dam-affected reaches, and for impact prediction and conservation planning in currently dam-free reaches of the Lancang River.

水电开发，尤其是梯级水电开发导致的生态环境问题已成为制约我国利用水能资源的重要因素。梯级水电开发引起的诸多环境问题中，对鱼类多样性的影响是社会关注的热点，也是影响我国水电可持续发展的关键。已有的研究多关注于局域尺度上大坝对鱼类的影响，而在流域尺度上的研究，尤其是关于功能多样性的影响研究非常有限，影响机制仍不清楚，制约了梯级开发河流鱼类资源的科学保护。本项目以澜沧江为研究区，通过大量野外采样和历史数据整理，获取梯级开发前后澜沧江鱼类物种组成和分布、鱼类功能性状和环境因子数据。在此基础上，1）从alpha和beta多样性水平揭示梯级开发对鱼类功能多样性的影响规律；2）基于澜沧江历史时期鱼类功能性状-环境因子关系，构建结构方程模型，阐明梯级开发引起的环境变化对鱼类功能多样性的影响机制。研究结果将为澜沧江已开发河段鱼类资源保护，待开发河段的拟建大坝对鱼类影响预测和保护规划提供科学数据和理论支撑。

梯级水电开发显著的改变了河流鱼类栖息地条件，导致鱼类多样性的持续降低。协调好梯级水电开发和鱼类资源保护之间的关系，是我国水电可持续发展的关键。已有关于梯级开发对鱼类影响的研究，多从单个梯级对物种多样性影响的角度开展，很少从流域尺度开展。因此，梯级开发如何驱动流域鱼类多样性变化的机制尚不清楚。本项目以正处于梯级开发进程中的澜沧江为研究区域，通过大量野外采样和历史数据整理，构建了澜沧江历史/现状鱼类空间分布数据库和功能性状数据库。在此基础上，从分类、系统发育和功能多样性层面，系统揭示了梯级水电开发影响下澜沧江鱼类多样性变化趋势、程度和规律。主要结果如下：澜沧江建坝河段土著鱼类的物种多样性显著减少，而未建坝河段土著种减少不显著。由于广布的土著种分布区域缩小和外来鱼类在特定河段的局域性入侵，鱼类系统发育多样性在所有河段均显著增加，同时流域鱼类群落表现出异质化趋势。在功能性状方面，梯级开发后，建坝河段鱼类平均体长增加，体型为圆筒形、移动能力弱和口下位鱼类的比例增加。功能多样性方面，梯级开发使鱼类功能丰富度、功能均匀度、功能离散度均升高，功能β多样性极显著增加。水环境变化、河流连通性降低和生物入侵，是导致澜沧江鱼类功能性状结构和功能多样性变化的关键因素。应将防控外来鱼类入侵（尤其是在库区），提升到与缓解水电开发对土著鱼类影响的同等重要的位置。本研究揭示的鱼类多样性变化趋势与机制，以及梯级开发河段土著种的减少率与梯级大坝之间的距离呈负相关关系等，对梯级电站的科学规划和梯级开发河流鱼类资源保护具有重要的指导意义。