Streamflow and hydrogen ion interrelationships identified using data-based mechanistic modelling of high frequency observations through contiguous storms

With the aim of quantifying the purely hydrological control on fast water quality dynamics, a modelling approach was used to identify the structure (and dynamic response characteristics or DRCs) of the relationship between rainfall and hydrogen ion (H⁺) load, with reference to rainfall to streamflow response. Unlike most hydrochemistry studies, the method used makes no a priori assumptions about the complexity of the dynamics (e.g., number of flow-paths), but instead uses objective statistical methods to define these (together with uncertainty analysis). The robust models identified are based on continuous-time transfer functions and demonstrate high simulation efficiency with a constrained uncertainty allowing hydrological interpretation of dominant flow-paths and behaviour of H⁺ load in four upland headwaters. Identified models demonstrated that the short-term dynamics in H⁺ concentration were closely associated with the streamflow response, suggesting a dominant hydrological control. The second-order structure identified for the rainfall to streamflow response was also seen as the optimal model for rainfall to H⁺ load, even given the very dynamic concentration response, possibly indicating the same two flow-paths being responsible for both integrated responses.