Reservoir artificial flood discharge is a critical driver for the compositional and functional shifts of dissolved organic matter in river mouth

While dam-based regulation modifies the natural transport rhythm of riverine materials, the effects of artificial flooding on river mouth dissolved organic matter (DOM) dynamics remain poorly constrained. The Water-Sediment Regulation Scheme in the Yellow River provides a unique snapshot. Distinct organic matter signatures were observed between the water release and sediment flushing phases using optical and molecular techniques. Here we show that during water release phase, rapid discharge of upper-layer water from Xiaolangdi Reservoir increased the proportion of bio-labile DOM in the Yellow River mouth. Conversely, during sediment flushing phase, resuspension and then release of bottom sediments from the reservoir enhanced aromatic DOM components. Although the relative abundance and composition of particulate organic matter remained unchanged during water release phase, it increased during sediment flushing phase. These findings demonstrate that reservoir operations reconfigure river-ocean carbon flows, emphasizing the need to integrate dam management strategies into global carbon cycling models. During water release, rapid discharge of upper-layer water from Xiaolangdi Reservoir increased bio-labile dissolved organic matter at the Yellow River mouth, while sediment flushing resuspended bottom sediments and enhanced aromatic components, as shown by optical spectroscopy and isotope analysis.