Land use and hydrological seasonality jointly regulate the composition and sources of riverine dissolved organic matter in the Three Gorges Reservoir region

Dissolved organic matter (DOM) is the most active form of organic carbon in rivers and plays a key role in biogeochemical processes. Understanding how land use change and seasonal hydrology regulate DOM dynamics is critical, particularly in monsoon regions with intensive human activities and hydrological variability. This study investigated the spatiotemporal variations in DOM composition and sources across different land use/land cover (LULC) types in representative rivers of the Three Gorges Reservoir (TGR) region during dry and wet seasons. In the dry season, DOM was dominated by protein-like, autochthonous components, whereas the wet season showed increased humic-like, terrestrial DOM with higher molecular weight and aromaticity. These seasonal variations were closely associated with changes in hydrological conditions. Rivers with higher forest cover exhibited more aromatic and allochthonous DOM signatures. In contrast, rivers influenced by urban and cultivated land use showed stronger signals of protein-like, autochthonous DOM, which were associated with higher nutrient levels and anthropogenic inputs. These results highlight the combined effects of monsoonal hydrology and land use on riverine DOM dynamics and provide insights for biogeochemical modeling and watershed management in the TGR region.