Redfield revisited: insights into freshwater seston C:N:P stoichiometry

Seston carbon (C), nitrogen (N), and phosphorus (P) stoichiometry plays a fundamental role in aquatic ecosystems, influencing nutrient cycling, primary and secondary production, and trophic interactions. In freshwater systems such as lakes, P limitation is more common, whereas in marine environments, N more frequently limits primary production, reflecting different nutrient limitation patterns across aquatic ecosystems. The Redfield ratio (C₁₀₆:N₁₆:P₁ molar), developed from marine seston, has long been considered a benchmark for nutrient composition and a predictor of nutrient limitation across aquatic ecosystems. A later global freshwater and marine seston survey proposed the Sterner ratio (C₁₆₆:N₂₀:P₁ molar) as a broader global seston average. We present the results of a fully replicated, multi-annual freshwater mesocosm experiment testing the effect of variable resource N:P stoichiometry on seston stoichiometry. We found that the seston C:N:P ratio aligned with the Redfield ratio under N-limited conditions, while P-limited conditions aligned with the Sterner global survey of freshwater ecosystems. Ternary plots offered visual insight into stoichiometric shifts, showing a trend toward P depletion relative to C and N as N:P supply increases. The average seston C:N:P ratio observed from our experimental data was C₁₄₁:N₂₂:P₁ (molar) and variation in seston C:N:P was small compared to the resource ratio gradient. Our mesocosm experiment showed that the Redfield ratio provides a useful description of seston stoichiometry in N-limited freshwater ecosystems. These findings advance the understanding of bottom-up controls on seston C:N:P stoichiometry and highlight the need to refine ecological theories regarding the application of the Redfield ratio in freshwater ecosystems.