Optimization of Parsimonious and Synchronized Discharge and Dissolved Organic Carbon Models Across Catchment Scales

The production, transport, loss, and export of dissolved organic carbon (DOC) are closely connected with hydrometeorological drivers. While terrestrial production depends on biogeochemical variables like soil moisture, air temperature, and the contact area between water and organic matter sources, export is determined by water availability and flow paths within soil storage. This study aims to quantify how hydrometeorological drivers jointly control DOC production and export across spatial scales in a temperate snow-dominated forested catchment. Using a parsimonious model to simultaneously optimize discharge and DOC concentrations, we leveraged over 14 years of high-resolution (15-min) hydrological data, along with weekly to monthly measurements of DOC concentrations, across nested catchments of varying sizes from small (7 km²), medium (170 km²), to large (480 km²). The simulations replicated daily hydrological (KGE ∼ 0.60) and DOC (KGE ∼ 0.60) concentration dynamics at all sites. Our findings indicate that shallow soil storage and antecedent precipitation (>45 days) significantly influence DOC dynamics across all three spatial scales, emphasizing the importance of connectivity in catchments' responses to hydrometeorological conditions. The influence of antecedent precipitation is of greater magnitude at larger scales, while pulses of DOC are more common at smaller scales due to rapid source activation. Our results highlight that model performance and the ability to realistically represent catchment processes are enhanced when hydrological and biogeochemical processes are considered simultaneously. Parsimonious models are crucial to evaluate how hydro-biogeochemical processes vary across spatial scales and ultimately respond to human perturbations, such as climate change and extreme events.