Fate of

the geographical location of the spill and an understanding of transport and fate could help ecologists determine the locations and species that might be affected. To illustrate the factors involved in the transport and the fate of oil, we will examine a more complicated situation where oil is spilled into the ocean.

Transport of Oil Surface transport

If an oil spill occurs in calm water, it moves according to gravity and its resistance by inertia, surface tension, and viscosity. Movement is terminated when an oil-specific slick thickness (c. 1 mm) is attained. In reality, wind, waves, and currents diffuse and break up the slick, spreading it to cover a much wider area. Slick thickness (volume divided by area) is not distributed uniformly, as the shape and thickness are elongated in the direction of the prevailing wind. In general, 90% of an oil spill's volume is distributed over 10% of its area.

Once an oil spill occurs, the oil is transported and degraded according to numerous physical, chemical, and biological processes (Figure 2). The chemical properties of oil, as determined by its components, will determine its environmental fate. Moreover, other factors such as location of the spill (land, river, or ocean) and weather conditions (temperature, wind speed, humidity) will impact the distribution and fate of oil. If a spill occurs on land, it may be somewhat easier to control and remediate. However, when oil spills into a river or the open ocean, there are more factors to consider. Knowledge of

Vertical transport

The vertical transport of oil depends on both vertical diffusivity and buoyancy. Vertical diffusivity transports droplets deeper into the water, while buoyancy raises the oil to the surface. The depth of oil droplet penetration is determined by oil properties such as the concentration in the dissolved phase, concentration in the droplet phase, droplet diameter, and the vertical diffusion coefficient. Ocean conditions, such as wave height, length, and period, and water density will alter the depth of oil transport. The vertical distribution of oil droplets will determine

Waves, currents, wind

Spreading

Water-in-oil emulsification

Biodegradation

Oil partitioned to water

Evaporation Photooxidation

Waves, currents, wind

Buoyancy

Vertical diffusivity

Oil-sediment agglomeration

Waves, currents, wind

Buoyancy

Vertical diffusivity

Oil-sediment agglomeration

Seafloor sediments Figure 2 Transport and fate of oil in the ocean.

greatly which types of marine species are affected. Sometimes, if oil is treated with surfactant-based dispersants, droplets become smaller and are able to penetrate the ocean more deeply. This has been a big concern for ecologists, since dispersants facilitate deeper transport of larger oil masses.

Horizontal subsurface transport

Under extremely calm weather conditions, vertically dispersed oil droplets can also rise to the surface, given sufficient time. However, in reality, it does not occur due to horizontal subsurface mixing which could ultimately dilute the oil. The process involved can be summarized in two steps: (1) scale-dependent diffusion and (2) shear dispersion. The latter mixing effect mainly results from the combination of velocity gradients with mixing in the direction of gradients.

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

Get My Free Ebook


Post a comment