Abstract With intensified dam construction in recent decades, river connectivity has been disrupted, reshaping elemental cycling and aggravating C: N: P imbalances. Here, we investigate how long‐term cascade damming regulates particulate C: N: P stoichiometry along the upper Yangtze River in China. We show that the contribution of autochthonous particulate organic carbon (A‐POC) gradually increases with reservoir age and hydraulic retention time, particularly near dams. Cascade impoundments stimulate reservoir‐induced phytoplankton production that increasingly outweighs terrestrial anthropogenic inputs, leading to a 39% decline in particulate C: N ratios from the upper reach of the Jinsha River to the Three Gorges Reservoir, approaching Redfield ratios. With continued operation, particulate C: N in reservoirs converges toward Redfield thresholds within ∼30 years of post‐impoundment, yet may fall below 6.625 after prolonged impoundment, altering the regulation of particulate C: P and N: P from particulate phosphorus (PP)‐dominated control to joint particulate organic matter–PP control. These results reveal the dual role of cascade reservoirs as both disruptors and gradual restorers of elemental balance, with long‐term ecological succession fostering stoichiometric convergence. Targeted regulation of phytoplankton biomass and watershed PP inputs is therefore essential for mitigating stoichiometric imbalance and guiding adaptive management in large dammed river–reservoir systems.
Zhang et al. (Wed,) studied this question.
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