Abstract：
The world\'s largest rivers are home to diverse, endemic, and threatened fish species. However, their sheer sizes make large-scale biomonitoring challenging. While environmental DNA (eDNA) metabarcoding has become an established monitoring approach in smaller freshwater ecosystems, its suitability for large rivers may be challenged by the sheer extent of their cross sections (>1 km wide and tens of meters deep). Here, we sampled fish eDNA from multiple vertical layers and horizontal locations from two cross sections of the lower reach of the Yangtze River in China. Over half of the ASVs (amplicon sequence variants) were detected in only a single combination of the vertical layers and horizontal locations, with ∼7% across all combinations. We estimated the need to sample >100 L of water across the cross-sectional profiles to achieve ASV richness saturation, which translates to ∼60 L of water at the species level. No consistent pattern emerged for prioritizing certain depth and horizontal samples, yet we underline the importance of sampling and integrating different layers and locations simultaneously. Our study highlights the significance of spatially stratified sampling and sampling volumes when using eDNA approaches. Specifically, we developed and tested a scalable and broadly applicable strategy that advances the monitoring and conservation of large rivers.
摘要：
世界上最大的河流是多种多样的，地方性,受威胁的鱼类物种。然而,它们的庞大规模使大规模生物监测具有挑战性。虽然环境DNA（eDNA）元转录编码已成为较小淡水生态系统中的一种既定监测方法，其对大型河流的适用性可能会受到其横截面范围(>1公里宽和几十米深)的挑战。这里,我们从中国长江下游两个横截面的多个垂直层和水平位置采样了鱼类eDNA。仅在垂直层和水平位置的单个组合中检测到超过一半的ASV（扩增子序列变体）。在所有组合中，有7%。我们估计需要在横截面剖面上采样>100升的水，以实现ASV丰富度饱和，这相当于物种水平的60L水。没有出现一致的模式来优先考虑某些深度和水平样本，然而，我们强调同时采样和整合不同层和位置的重要性。我们的研究强调了使用eDNA方法时空间分层抽样和抽样量的重要性。具体来说,我们开发并测试了可扩展和广泛适用的策略，以促进大型河流的监测和保护。
