Data for LongTan reservoir

Extensive reservoir construction has fragmented more than 70% of the world's rivers, with major implications for river connectivity and carbon cycling. However, it remains unclear how riverine DOM responds to reservoir influence and its potential impact on downstream systems. Here, we used multiple means, including Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), radiocarbon and environmental factors, to investigate the dynamic changes of DOM and its controlling factors under different hydrological management regimes in the largest reservoir (LongTan Reservoir) located in the Pearl River, the second largest river in China in terms of water discharge. Our results suggest that the molecular diversity of riverine DOM is reduced in the reservoir, and oxygen-rich compounds and heteroatomic compounds, such as nitrogen-, sulfur- and phosphorus-containing compounds, are preferentially removed by enhanced photo- and biodegradation in the reservoir area, especially during the storage period, resulting in DOM enriched with oxygen-poor compounds and a biodegraded Δ¹⁴C value to the downstream. This study highlights that the composition of riverine DOM will be significantly modified by the reservoir, but these reservoir effects could be further controlled by setting an ideal outlet location