Evaluating the performance of CE-QUAL-W2 version 4.5 sediment diagenesis model

Abstract. This research evaluates the performance of the CE-QUAL-W2 v4.5 sediment diagenesis model in simulating water temperature, dissolved oxygen, total phosphorus, total nitrogen, chlorophyll a, and biochemical oxygen demand in a Portuguese reservoir over a six-year period (2016–2021). The model was calibrated using 35 observed profiles of temperature and dissolved oxygen, as well as six annual measurements of total nitrogen, total phosphorus, chlorophyll a, and biochemical oxygen demand at multiple depths. To benchmark performance to the sediment diagenesis model, three alternative sediment oxygen demand formulations – a Zero-order, First-order, and a Hybrid model combining both approaches – were also implemented and compared. All models achieved NSE and RMSE values within or near the ranges reported in the literature, effectively capturing the system's water quality dynamics. Among them, the Hybrid model yielded the best overall performance while maintaining a simpler structure (Water temperature – NSE: 0.96±0.18; RMSE: 1.09±0.23 °C; Dissolved oxygen – NSE: 0.76±0.30; RMSE: 1.87±0.72 mg L−1). The sediment diagenesis model exhibited similar performance metrics (Water temperature – NSE: 0.95±0.18; RMSE: 1.13±0.28 °C; Dissolved oxygen – NSE: 0.71±0.14; RMSE: 2.01±0.59 mg L−1). Overall, the results suggest that the diagenesis model may be better suited for capturing detailed process-based dynamics over extended timeframes, whereas simpler models, such as the Hybrid model, are more appropriate for short- to medium-term applications or situations with limited data availability. Hopefully, the results of this study will help improve water management strategies by supporting more informed model selection tailored to the temporal scope and data constraints of reservoir monitoring programs.