Potential Marine Environmental Impacts of Ammonia Releases during Bunkering: A Simulation Analysis Using a Coupled Eutrophication and Hydrodynamic Model in the Singapore Strait

To reduce greenhouse gas (GHG) emissions from the marine industry and mitigate global warming, ammonia is being considered as a premising alternative to traditional fossil fuels. As one of the world’s busiest ports, Singapore is actively exploring ammonia bunkering as part of its decarbonization strategy. However, before initiating ammonia bunkering operations, an environmental impact assessment (EIA) addressing potential ammonia leakage is crucial.This study employs a coupled eutrophication model with nine biogeochemical variables integrated into a high-resolution hydrodynamic model of Singapore’s coastal waters to evaluate the potential marine environmental impacts of ammonia releases during bunkering. This model is calibrated using hourly sea surface level data from Tanjong Pagar and dissolved oxygen measurements from Kusu Island, demonstrating robust performance in simulating diurnal variations in biogeochemical variables and the tidal dynamics, with a horizontal resolution ranging from 60 to 300 meters and a temporal resolution of 3 minutes.Using coral and fish as key receptors in the Singapore Strait, ammonia concentration thresholds for 50% lethality within 48 hours (LC50) were from the literature: 0.057 mg N/L for coral (LC50Coral) and 2.1 mg N/L for fish (LC50fish). Sensitivity experiments were conducted to evaluate the spatial extent and duration of ammonia toxicity under different scenarios, varying release locations, flow rates, timings. Results indicate that ammonia dispersion near jetties is slower due to weaker currents and structural obstructions, resulting in localized impacts on coral that can persist for one to several days, depending on release volume. Conversely, in deep water areas with stronger currents and obvious tidal influence, ammonia disperses more rapidly, with coral toxicity effects lasting only a few hours. Furthermore, the magnitude of toxicity increases with higher release volumes, and release time significantly influences the plume’s direction, affected area, and duration, thereby altering its impact on marine life. The study also examines changes in nitrate concentrations and the potential for eutrophication associated with ammonia release. These findings provide critical insights into the environmental risks of ammonia bunkering in the Singapore Strait and inform mitigation strategies to minimize ecological impacts.