Spatiotemporal Dynamics and Hydrological Controls of Dissolved Organic Carbon Export From the Dongting Lake Basin

ABSTRACT

Dissolved Organic Carbon (DOC) is a major component of the lateral carbon export from terrestrial to aquatic ecosystems and plays a key role in regional carbon cycling and water quality. However, the long‐term dynamics and hydrologically driven fluxes of DOC remain poorly understood at the watershed scale. Here, we applied the improved process‐based model of TRIPLEX‐HYDRA to quantify runoff and DOC dynamics across the Dongting Lake Basin, China, from 2012 to 2024. The result demonstrated that the model performed well and successfully reproduced the river network. The model generally captured runoff dynamics across the four major tributaries, with R ² and NSE values of 0.50–0.61, and bias ranging from −8.35% to 0.49%. Simulated DOC concentrations were also in reasonable agreement with observations from the Zi River, with a correlation coefficient (CC) of 0.66 and a relatively low bias of −4.01%. Soil DOC leaching showed a widespread increasing trend across 75.78% of the basin, with statistically significant increases in 29.86% of the area over the study period, and exhibited higher fluxes in the southwestern basin and lower fluxes in the northern region. Annual terrestrial DOC input to the river network ranged from 0.241 to 0.287 Tg C year ⁻¹ , while net DOC export to Dongting Lake ranged from 0.185 to 0.218 Tg C year ⁻¹ , with the Xiangjiang and Yuanjiang as the dominant contributors. Basin‐scale mass‐balance and mechanism analyses further demonstrated that riverine DOC export was jointly regulated by the terrestrial DOC supply, hydrological transport, and in‐stream processing, rather than by hydrological routing alone. Overall, this study provides the first comprehensive assessment of DOC export and dynamics in the Dongting Lake Basin, offering a valuable insight into watershed‐scale carbon cycling processes and their hydrological controls.