Nutrient-driven dissolved organic matter composition and its regulation on carbon sequestration in aquatic regions: Insights from reservoirs, rivers, and offshore ecosystems.

Conservation and management of organic carbon (OC) pools in aquatic regions are vital for enhancing carbon sequestration. However, whether the influence of nutrient-driven dissolved organic matter (DOM) composition on OC dynamics is convergent or divergent across aquatic systems remains unclear. This study selected 124 sediment sites from rivers, reservoirs, and offshore areas to investigate the relationships between DOM components, OC fractions, and environmental parameters. OC pools from different aquatic regions have similar distributions, with particulate OC (POC) and mineral-associated OC (MAOC) accounting for 90% of the total OC pool. DOM's sources and compositions differ in those aquatic ecosystems. In rivers and reservoirs, DOM mainly comes from allochthonous inputs, demonstrating a high degree of humification and a large molecular weight. Offshore DOM is characterized by a smaller molecular weight and lower humification; it receives inputs from both allochthonous and autochthonous sources, with the latter predominating. DOM composition (66.81%) and environmental parameters (33.19%) jointly regulate OC pool dynamics across aquatic regions, with DOM composition being the key influencing factor. Specifically, available phosphorus, total nitrogen, nitrate nitrogen, and ammonium nitrogen affect autochthonous DOM, which in turn influences MAOC distribution. By contrast, allochthonous DOM is only influenced by phosphorus forms and contributes to increased POC. Compared with allochthonous DOM, autochthonous DOM has a greater effect on sediment OC. These findings emphasize the importance of "multisource" carbon management for sustaining OC sinks in aquatic environments and providing a theoretical framework for optimizing carbon-neutral development.