Modeling study on oil spill transport in the Great Lakes: The unignorable impact of ice cover.

The rise in oil trade and transportation has led to a continuous increase in the risk of oil spills, posing a serious worldwide concern. However, there is a lack of numerical models for predicting oil spill transport in freshwater, especially under icy conditions. To tackle this challenge, we developed a prediction system for oil with ice modeling by coupling the General NOAA Operational Modeling Environment (GNOME) model with the Great Lakes Operational Forecast System (GLOFS) model. Taking Lake Erie as a pilot study, we used observed drifter data to evaluate the performance of the coupled model. Additionally, we developed six hypothetical oil spill cases in Lake Erie, considering both with and without ice conditions during the freezing, stable, and melting seasons spanning from 2018 to 2022, to investigate the impacts of ice cover on oil spill processes. The results showed the effective performance of the coupled model system in capturing the movements of a deployed drifter. Through ensemble simulations, it was observed that the stable season with high-concentration ice had the most significant impact on limiting oil transport compared to the freezing and melting seasons, resulting in an oil-affected open water area of 49 km2 on day 5 with ice cover, while without ice cover it reached 183 km2. The stable season with high-concentration ice showed a notable reduction in the probability of oil presence in the risk map, whereas this reduction effect was less prominent during the freezing and melting seasons. Moreover, negative correlations between initial ice concentration and oil-affected open water area were consistent, especially on day 1 with a linear regression R-squared value of 0.94, potentially enabling rapid prediction. Overall, the coupled model system serves as a useful tool for simulating oil spills in the world's largest freshwater system, particularly under icy conditions, thus enhancing the formulation of effective emergency response strategies.

A generic approach to construct pseudo components for oil weathering models.

Oil weathering models are essential for predicting the behavior of spilled oil in the environment. Most models use a "Pseudo Component" (PC) approach to represent the wide range of compounds found in petroleum products. Within the approach, rather than modeling each individual compound in an oil, a manageable number of PCs are developed that represent whole classes of compounds. However, previous studies focused mainly on traditional crude oils and did not develop a generic approach to create an optimal set of PCs for a variety of oils. In developing the updates to the NOAA oil weathering model, we propose herein a generic approach to construct PCs using oil distillation data to capture the complexity of oil evaporative weathering. We validated our approach with 899 oils from the Automated Data Inquiry for Oil Spills (ADIOS) oil library and found that an optimal set of sixteen PCs should be used. These PCs include two with low boiling point (below 144 °C), one with a high boiling point (above 400 °C), and thirteen constructed within a middle range of boiling points with a temperature resolution of 20 °C. Our simulation tests suggested that this set of sixteen PCs adequately characterizes oil evaporation processes for a wide variety of oils.

Oil biodegradation in permeable marine sediments: Effects of benthic pore-water advection and solute exchange.

Oil spills have been recognized as among the worst kinds of environmental disasters, causing severe coastal ecological and economic damages. Although benthic flow and solute fluxes are known to have strong impacts on fate and transport of oil deposited within marine sediments, their endogenous mechanisms still remain to be uncovered. In this paper, simulations of flow and solute transport processes along with hydrocarbon biodegradation were conducted in a cylindrical benthic chamber system to investigate influences of benthic hydrodynamics on oil biodegradation in permeable marine sediments. Results show that ripple-flow interactions create subsurface recirculation cells whereby seawater infiltrates into the benthic sediments at ripple troughs while groundwater discharges near the crests. It results in a spatially varied oil biodegradation rate in marine sediments. Significant oil biodegradation occurs near sediment ripple troughs due to direct oxygen recharge, while biodegradation of oil deposited uphill becomes slow due to limited oxygen replenishment. Oil biodegradation decreases subsurface oxygen content, and consequently impedes discharge of oxygen from benthic sediments. Our results reveal a dynamic interaction between oil biodegradation and benthic flow and solute transport processes, which has strong implications for predicting oil persistence and biodegradation within marine sediments and its associated impacts on benthic biogeochemical processes.

Oil spill modeling in deep waters: Estimation of pseudo-component properties for cubic equations of state from distillation data.

Deep-water oil spills represent a major, localized threat to marine ecosystems. Multi-purpose computer models have been developed to predict the fate of spilled oil. These models include databases of pseudo-components from distillation cut analysis for hundreds of oils, and have been used for guiding response action, damage assessment, and contingency planning for marine oil spills. However, these models are unable to simulate the details of deep-water, high-pressure chemistry. We present a new procedure to calculate the chemical properties necessary for such simulations that we validate with 614 oils from the ADIOS oil library. The calculated properties agree within 20.4% with average values obtained from data for measured compounds, for 90% of the chemical properties. This enables equation-of-state calculations of dead oil density, viscosity, and interfacial tension. This procedure enables development of comprehensive oil spill models to predict the behavior of petroleum fluids in the deep sea.