Author(s): Ge Yang; Yuntong She; Wenming Zhang

Linked Author(s): Ge Yang

Keywords: Water quality; Cold region; Ice effect; Spatial and temporal variability

Abstract: Urban rivers in cold regions face unique water quality challenges which are compounded by the complex interactions of environmental, anthropogenic, and climatic factors. The discharge of sanitary and industrial wastewater into rivers impacts instream water quality. The seasonal formation of ice cover can significantly alter river hydrodynamics, thereby affecting many water quality processes. Despite its significance, river water quality under ice-covered conditions remains understudied as compared to the open water seasons. Understanding the full spectrum of water quality throughout the year is essential for comprehensive river management. In this study, one-dimensional and two-dimensional modelling of water quality in the North Saskatchewan River (NSR) during open water and ice-covered periods was performed using the Environmental Fluid Dynamics Code (EFDC+). Four nitrogen species (ammonia/ammonium (NHx), nitrate/nitrite (NOx), total organic nitrogen (TON) and total nitrogen (TN) ) were modelled. The EFDC+ model was calibrated and validated using historical observed data from 2000 to 2021. The model has good performance in hydrodynamics and water quality simulation under both open water and ice-covered conditions (mean absolute error (MAE) = 0.001 mg/L - 0.968 mg/L; relative mean error (|RME|) = 0.34% - 67.05%). The model indicated that the annual average TN concentrations initially increased but later declined over the simulated period, peaking between 0.55 mg/L and 0.10 mg/L in 2011 across six monitoring sites. TN concentrations generally increase in the downstream direction along the NSR. In the upstream reach, TN concentrations during the ice-covered period were 16.0% to 20.2% lower than those during the open water period. In contrast, TN concentrations during the ice-covered period were 15.8% to 19.0% higher than those during the open water period in the downstream reaches. This study provides insights for river water quality monitoring and management in cold regions.

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P1660-cd

Year: 2025