Isotope-Based Calibration to Inform Water Quality in Hydrological Modelling

Improving the accuracy of water quality modelling is of great importance to resource management worldwide, particularly for agricultural catchments where the issue of eutrophication is prevalent. This study's objective was to incorporate isotope O precipitation and streamflow data into the calibration of a hydrological model to inform streamflow subcomponents and subsequently the transport of nutrients inorganic nitrogen (IN) and total phosphorous (TP). The study areas entailed two agricultural catchments which were Nissouri Creek and Big Creek located in southern Ontario. The HYPE model is a physically-based, semidistributed model that was utilized for three experimental phases entailing hydrometric-isotope calibration, hydrometric and nutrient calibration, and hydrometric, isotope and nutrient calibration, with an additional version of each phase entailing the exclusion of event isotope data. The isotope data calibrated poorer simulations of discharge and nutrient simulations, with inorganic nitrogen performing the worst with only baseflow isotopes with an NSE of -35.661 for Big Creek whereas with event isotopes was the worst IN simulation for Nissouri Creek with an NSE of -8.749. However, it was found that isotope data did alter streamflow subcomponents compared to hydrometric-only calibration through reducing simulated total annual evaporation and increasing runoff. Therefore, while isotope data can introduce further complexity, it acts as an additional metric for performance that can explore alternative simulation possibilities to that of hydrometric-only calibrated models and bridge the research gap between hydrology and water quality modelling.