Reservoir operation regulates the dynamics of dissolved organic matter in sediments

In this study, for Three Gorges Reservoir (TGR), which is recognized as one of the world's largest reservoirs, we primarily explore the underlying mechanism of the variations of dissolved organic matter (DOM) in sediments through the application of radiocarbon (Δ¹⁴C) isotope, optical and molecular techniques, and subsequently assess the monthly and annual variation of DOM in sediments from 2011 to 2080 with the development of a DOM molecules-related numerical model. The findings suggested that variations of primary productivity and hydrological conditions influenced by reservoir operation likely modulated the dynamics of DOM in sediments of TGR. Laboratory analysis demonstrated that there was more autochthonous DOM in sediments with a declining pattern from upstream to downstream in the wet season, and more allochthonous DOM in sediments with no spatial trend in the dry season. Moreover, based on the numerical simulation, from 2011 to 2080, July, April, and September hold major (>50 %) of the year's accumulation of allochthonous and autochthonous DOM in sediments. By 2080, the quantities of allochthonous and autochthonous DOM in sediments in TGR would reach 1166 × 10⁴t and 129 × 10⁴t, respectively. Our work provides detailed insights into the dynamics of organic matter (OM) pool in reservoirs, which would enhance comprehension regarding the ecological impact of reservoir construction on aquatic ecosystems.