Is a simple model based on two mixing reservoirs able to reproduce the intra-annual dynamics of DOC and NO3 stream concentrations in an agricultural headwater catchment?

Agriculture disturbs the biogeochemical cycles of major elements, which alters elemental stoichiometry surface stream waters, with potential impacts on their ecosystems. However, models catchment hydrology and water quality remain relatively disconnected, even though observation that dissolved organic carbon (DOC) nitrate (NO3−) have opposite spatial temporal patterns seems relevant for improving our representation hydrological transport pathways within catchments. We tested ability a parsimonious model to simultaneously reproduce intra-annual dynamics flow, DOC NO3− concentrations using 15 years daily data from small headwater agricultural (AgrHyS observatory). The consists an unsaturated reservoir, slow reservoir representing groundwater fast riparian zone preferential flow paths. sources are assumed behave as infinite pools fixed concentration in each contributes stream. Stream thus result simple mixing contributions. reproduced annual storm-event discharge, stream, calibration KGE scores 0.77, 0.64 0.58 respectively, validation 0.72, 0.43 respectively. These results suggest these can be explained by processes temporally variable contributions (NO3− rich poor) reservoirs (DOC poor), poor transformations. Unexpectedly, time series calibrate increased uncertainty parameters control fluxes model. legacy storage resulting history studied supports assumption main at scale several years. Nevertheless, reproducing long-term trends solute would require additional information about reservoirs.