Combined Effects of Human Activity and Rainfall Shape the Differentiated Relationships of Concentration–Discharge in the Yangtze and Yellow River Basin, China

Concentration–discharge (C–Q) relationships provide valuable insights into spatial variation in hydrological processes and catchment dynamics. However, research on the influence of catchment characteristics and constituents across large spatial scales remains limited. Furthermore, the key factors that shape C–Q relationships for solutes vary considerably across different geographical regions. This study analyzed water‐quality data collected from 2021 to 2023 from 32 catchments in the Yangtze and Yellow River basins (YRZB and YRB) in China. The focus is on understanding the spatial variability of dissolved oxygen (DO), turbidity (TU), total phosphorus (TP), and total nitrogen (TN) concentrations. Conclusions are as follows: (1) TU and DO exhibit consistent behavior across both river basins. TU is characterized by enrichment (b > 0 and CVC/CVQ > 0.5), while DO shows consistent dilution (b < −0.2 and CVC/CVQ < 0.5). These enrichment/dilution patterns are more pronounced in the Yellow River Basin compared to the Yangtze River Basin. (2) In contrast, the Yellow River Basin exhibits TN enrichment (b > −0.2), while TP behaves chemostatically (−0.2 < b < 0.2). (3) Spatial variation in rainfall regime is the primary driver of differences in solute export (DO, TU) across catchments, with concentrated rainfall in specific Yellow River catchments leading to more pronounced enrichment or dilution effects. (4) Urbanization significantly influences TP enrichment in the Yangtze River Basin, while agricultural activities drive TN enrichment in the Yellow River Basin. These findings enhance the understanding of the relative importance of solute properties and catchment characteristics in shaping the hydrological and biogeochemical functions of basins affected by urbanization and agriculturalization.