Evaluating Fecal Coliform Transport under Hydroclimatic and Pollution Scenarios in Xiwei Reservoir Using EFDC

Fecal coliform (FC), as an important indicator of microbial contamination, plays a critical role in water quality assessments and environmental health management. Due to the high cost and limited temporal resolution of traditional monitoring approaches, process-based modeling provides a useful framework for evaluating FC transport and persistence in reservoir systems. In this study, Environmental Fluid Dynamics Code (EFDC) was applied to simulate the hydrodynamics, water temperature, and FC dynamics in Xiwei Reservoir, China under different hydroclimatic and pollution scenarios. The FC decay rate was calibrated over a range of 0.25–1.60 day −1 , and 0.25 day −1 was selected as the optimal value. The model reproduced the observed variations in water level, temperature, and FC concentration, with Mean Absolute Percentage Errors of 0.07%, 4.9%, and 4.2%, respectively. The results show that wet and warm conditions were associated with slightly higher FC concentrations (∼8%) compared with the wet and cold conditions based on the meteorological data from 2005 to 2024. The simulations further demonstrate that hydrodynamic conditions influence FC transport and persistence. FC concentrations were generally higher in regions with limited water exchange, indicating the importance of hydrodynamic controls on contaminant persistence. Under extreme pollution scenarios with initial FC concentrations of 100,000 MPN/L, elevated FC recovery may require up to 50 days following extreme contamination events, particularly near inflow regions. Although the present model does not explicitly incorporate diffuse runoff inputs, sediment interactions, nutrient dynamics, or aquatic biological processes, the study provides a useful framework for evaluating FC responses under different hydroclimatic and pollution conditions. The results offer practical insights into reservoir water quality management and FC risk control under data-limited conditions.