Spatiotemporal variations in dissolved organic carbon in China’s major river basins and their associations with climate change and human activities

Riverine dissolved organic carbon (DOC) is a vital element of regional carbon cycling, yet its magnitude and influencing factors remain poorly quantified. Existing large uncertainties in the distribution, trends, and drivers of DOC compromise the accuracy of terrestrial carbon budget estimations. This study compiled 1922 DOC data points from literature on four major Chinese river basins (i.e., the Songhua River Basin, Yellow River Basin, Yangtze River Basin, and Pearl River Basin) for the period 1997-2023. The spatiotemporal patterns and driving mechanisms of DOC in these basins were quantified and systematically analyzed. Key results are as follows: [1] Spatially, DOC concentration (C_DOC) exhibited a distinct "north high, south low" pattern nationally, while DOC flux (F_DOC) displayed an inverted "south high, north low" distribution. Temporally, C_DOC in the four basins all showed a statistically significant increasing trend, with an average annual rise of 0.04 mg L⁻¹ yr⁻¹. Meanwhile, the F_DOC into the sea in the Yangtze River Basin and Yellow River Basin also exhibited a statistically significant increase, with an average annual growth of 0.05 Tg yr⁻¹ [3]. Attribution analysis indicated that the spatiotemporal distribution of C_DOC was influenced by both climatic factors and human activities, whereas that of F_DOC was controlled primarily by streamflow. The findings of this study reflect the national distribution and dynamics of DOC in major Chinese rivers, and provide a valuable framework together with details of key parameters to support future research into global riverine carbon cycle models.