Long-Term Meromixis in a Subarctic Mine Site Pit Lake: Evaluation of a One-Dimensional Hydrodynamic Model

The ability to robustly predict meromixis in pit lakes has important implications for mine water management. We present a one-dimensional hydrodynamic model (PitMod) of a sub-arctic meromictic pit lake (Colomac Zone 2 Pit, Northwest Territories, Canada; 64.397°N, -115.088°W) calibrated using 9 years of mooring data and 25 vertical profiles. Calibration focused on light extinction, wind drag, surface heat flux coefficients and turbulent diffusion around the chemocline. The model successfully reproduced observed seasonal thermal dynamics in the moorings with an Root Mean Square Error (RMSE) of 1.1°C, and captured the stratification of the profiles with an RSME for temperature of 0.72°C and TDS of 0.007 g L⁻¹. Although mixing across the chemocline remained weak, turbulent diffusion was essential to reproduce the observed broadening of the TDS gradient. Model performance compared favorably with other one-dimensional lake models, demonstrating that PitMod is a suitable tool for evaluating long-term meromixis and water quality in mine pit lakes.