Emergent archetype patterns of coupled hydrologic and biogeochemical responses in catchments

Relationships between in-stream dissolved solute concentrations (C) and discharge (Q) are useful indicators of catchment-scale processes. We combine a synthesis of observational records with a parsimonious stochastic modeling approach to test how C-Q relationships arise from spatial heterogeneity in catchment solute sources coupled with different timescales of reactions. Our model indicates that the dominant driver of emergent archetypical dilution, enrichment, and constant C-Q patterns was structured heterogeneity of solute sources implemented as correlation of source concentration to travel time. Regardless of the C-Q pattern, with weak correlation between solute-source concentration and travel time, we consistently find lower variability in C than in Q, such that the predominant solute export regime is chemostatic. Consequently, the variance in exported loads is determined primarily by variance of Q. Efforts to improve stream water quality and ecological integrity in intensely managed catchments should lead away from landscape homogenization by introducing structured source heterogeneity.