Invasive aquatic plants can have various ecological impacts on river ecosystems. It is important to identify the spatial positions of the invasive aquatic plant sources in a mainstem-tributary network to understand the distributions and prioritize the removal areas of invasive aquatic plants. This study used environmental DNA (eDNA) analyses to identify the potential sources (invasive macrophyte patches that persist throughout seasons in a river segment and can provide the plant fragments to the downstream) of Egeria densa, an invasive aquatic macrophyte, in a riverine network. We monitored the seasonal changes (March, July, August, and October) of eDNA concentrations of E. densa in tributaries with their associated mainstem sites (total 16 × 2 = 32 sites) in the Gonokawa River, Japan in 2021 and identified the potential sources of the target species based on the spatial abundance patterns and persistence in the riverine network. Our results indicated that the eDNA concentrations of E. densa have decreased in the mainstem from March to October, whereas the eDNA concentrations in the tributary sites had opposite temporal patterns possibly because the artificial tributary sites could be less affected by the flood event. In addition, certain mainstem segments and tributaries had higher eDNA concentrations and persistence of E. densa than other locations and could be potential sources of the invasive macrophyte in the system. Our study helps to identify and remove the potential sources of invasive macrophytes and prevent the further spread in riverine systems.

入侵的水生植物会对河流生态系统产生各种生态影响。识别干支流网络中入侵水生植物源的空间位置，以了解入侵水生植物的分布并优先排除入侵水生植物的区域，这一点很重要。本研究使用环境 DNA (eDNA) 分析来确定河流网络中侵入性水生大型植物Egeria densa的潜在来源（在河流段的整个季节持续存在的侵入性大型植物斑块，并可向下游提供植物碎片） 。我们监测了E. densa的 eDNA 浓度的季节性变化（3 月、7 月、8 月和 10 月）2021 年在日本 Gonokawa 河的支流及其相关干流站点（总共 16 × 2 = 32 个站点）中，并根据河流网络中的空间丰度模式和持久性确定了目标物种的潜在来源。我们的研究结果表明， 3 月至 10 月干流E. densa的 eDNA 浓度有所下降，而支流站点中的 eDNA 浓度具有相反的时间模式，这可能是因为人工支流站点受洪水事件的影响较小。此外，某些主干节段和支流具有较高的 eDNA 浓度和E. densa的持久性与其他位置相比，可能是系统中入侵大型植物的潜在来源。我们的研究有助于识别和消除入侵大型植物的潜在来源，并防止在河流系统中进一步蔓延。