Hydrological water quality modelling of nested meso scale catchments

HYPE (Hydrological Predictions for the Environment) model was applied for simulation of discharge and streamwater inorganic nitrogen (IN) concentration in two different meso scale catchments of the German lower mountain range, the Selke (463 km2) and Weida catchments (99 km2). DREAM(ZS) (DiffeRential Evolution Adaptive Metropolis algorithm) was combined with the HYPE model to implement parameter calibration and uncertainty analysis. Results showed that IN concentration and daily IN load had a proportional relationship with discharge, indicating that IN leaching is mainly controlled by runoff. The HYPE model was proved to be capable of capturing dynamics and balances of water and IN load with a Nash-Sutcliffe coefficient above 0.83. Multi-site calibration improved model performances at internal sites and decreased parameter posterior uncertainty ranges as well as prediction uncertainty. Compared with calibration using bi-weekly measurements, nitrogen-process parameters calibrated using daily averages of nitrate-N concentration observations produced better and more robust IN modelling performance, narrower posterior parameter uncertainty ranges and IN prediction uncertainty.