Oil in the Sea III Inputs, Fates, and Effects (2003) / Chapter Skim
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4. Behavior and Fate of Oil
4. Behavior and Fate of Oil
Pages 89-118
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From page 89... ...
Mass loadings, however, are not a direct indicator of the potential effects of petroleum hydrocarbons in the oceans. Ecological and human health risks generally scale to the magnitude and duration of exposure, and these mass loading rates must be translated for all hydrocarbon sources into temporally and spatially variable concentrations in the sea.
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From page 90... ...
This chapter concludes with a discussion of conceptual and computer models and a summary of fates of oil inputs to the ocean from seeps, surface spills, deepwater releases, and diffuse sources such as the atmosphere, land run off, and recreation. PROCESSES THAT AFFECT THE IMPACT OF OIL RELEASES Weathering Following an oil spill or any other event that releases crude oil or crude oil products into the marine environment, weathering processes begin immediately to transform the materials into substances with physical and chemical characteristics that differ from the original source material.
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From page 91... ...
and detailed interactions (B) of a conceptual model for the fate of petroleum in the marine environment.
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From page 92... ...
Water can be simply "entrained" by the oil due to viscous forces, without forming a more stable emulsion. Thus, emulsification also has significant effects on the choice of oil spill recovery methods.
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From page 93... ...
In contrast, the solubility of the aliphatic oil components is very low relative to that of aromatic hydrocarbons and is considered to be negligible. The solubility of crude oils and petroleum products was investigated by Shin et al.
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From page 94... ...
Where oxygen and sunlight are excluded in anoxic environments, anaerobic microbial oxidation takes place. Photooxiclation in Sea Water Photooxidation is a family of light-catalyzed reactions that oxidize the reduced carbon in petroleum hydrocarbons.
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From page 95... ...
The aromatic and unsaturated fractions of dissolved petroleum hydrocarbons undergo both direct and indirect photolysis in seawater. Polycyclic aromatic hydrocarbons (PAM)
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From page 96... ...
produced in the breakdown of hydrocarbons. Anaerobic degradation of hydrocarbons by sulfate- and iron-reducing bacteria has recently been measured in marine environments (Loveley et al., 1995, Coates et al., 1996~.
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From page 97... ...
Rates for anaerobic degradation of hydrocarbons have not been measured but are generally thought to be a fraction of aerobic respiration rates. In marine environments subject to oil spills (e.g., harbors)
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From page 98... ...
Second, LC can create convergence and divergence zones on the surface that affect oil thickness, which in turn can affect biota, weathering rates, and cleanup strategies. Finally, LC enhances vertical dispersion of oil droplets.
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From page 99... ...
Theory suggests that wave breaking will drive oil droplets roughly one wave height into the water column, whereas LC could drive smaller near-neutrally buoyant droplets tens of meters down, perhaps as far as the base of the mixed layer. Given this, it is an apparent paradox that stateof-the-art oil spill trajectory models include vertical dispersion due to wave breaking but not LC.
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From page 100... ...
Vertical Dispersion and Entrainment Vertical dispersion and entrainment are the movements of oil droplets of sizes less than about 100,um into the water column. Typically droplets that display a residence time of minutes to hours have droplet sizes less than about 20 ,um (Reed, 1992~.
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From page 101... ...
the oil becomes stranded on a shoreline. Partitioning and Bioevailability Partitioning Petroleum hydrocarbons come in many chemical forms or species and partition among the myriad particulate and
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From page 102... ...
The composition of sedimentary organic matter also affects the efficiency with which benthic organisms extract PAH from sediments (Landrum et al., 1997; Standley, 1997; Weston and Mayer, 1998; Baumard et al., 1999~. Bioavailability Organisms are exposed to petroleum hydrocarbons in the marine environment.
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From page 103... ...
A coastal zone oil spill model (COZOIL) was developed to predict the behavior, loading, and fate of oil stranded on different shoreline types (Reed and Gundlach, 1989~.
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From page 104... ...
In addition, efforts to distinguish anthropogenic and natural crude oil contamination of coastlines should continue so that the role of natural seepages, over which humankind has little control, and anthropogenic spills of crude oil and refined products, which humankind is able to minimize, can be readily and accurately distinguished. Oil and Ice The behavior and fate of oil in the Arctic, and in other ice-containing marine environments, is modified by the presence of the ice and by the lower temperature (Fingas and Hollebone, 2001~.
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From page 105... ...
Fates of Subsurface Releases Oil spills sometimes are not released at the surface but further down in the water column. Examples include natural seeps, blowouts during drilling of exploratory wells, pipeline leaks, and shipwrecks.
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From page 106... ...
If a substantial quantity of oil reaches the surface, spreading will occur, driven by gravity forces and restrained by surface tension and viscous forces in a manner similar to a surface slick. If there is insufficient integrated buoyancy to set up the plume dynamics described above, the droplets or bubbles rise as individual elements at the rise velocity dictated by their diameter and shape.
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From page 107... ...
Hydrate formation is an important factor in determining how quickly oil rises to the surface. Hydrate has a specific Current In, _~~ |r ~ Terminal 31V Layer ~ _ Entrained Water Gas Hydrate Stratified Water FIGURE 4-6 Schematic diagram depicting the basic physical processes involved in a deepwater subsurface oil and gas release.
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From page 108... ...
Figure 4-1 illustrates this conceptual model, which partitions the marine environment into three interdependent environmental compartments or modules the water column, bottom sediments, and biota. The various mechanisms whereby petroleum hydrocarbons move from one module to another are identified on the figure.
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From page 109... ...
The Bottom -Seclim en t Moclule The bottom sediments module shown on Figure 4-1 is also a fates module describing (1) chemical weathering of petroleum hydrocarbons within the sediment, (2)
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From page 110... ...
Writing an ingestion-growth-excretion relationship for each trophic level and coupling trophic levels with a predatorprey relationship would enable one to track the migration of petroleum hydrocarbons through the food chain and to determine the concentration of the petroleum hydrocarbons per gram of biomass at each trophic level. Ingestion into the food chain would be a sink for petroleum hydrocarbons in the water-column or bottom-sediment modules, and petroleum hydrocarbons excreted in the biota module would become sources for the water-column or bottom-sediment modules.
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From page 111... ...
In this model, one knows where the spill ended up but needs to determine the most likely origin to identify the responsible party. There have been two reviews of composite oil slick models published recently: ASCE (1996)
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From page 112... ...
Oxidation rankings reflect the relative rate and extent of oil removal by microbial and photooxidative degradation for those oils that have moderate persistence in the marine environment. Thus, releases of crude oils are ranked "medium" because microbial degradation is a significant weathering process for the intermediate-weight hydrocarbon components in crude oil, whereas releases of heavy, weathered oils are ranked "low" because they are recalcitrant to microbial and photodegradation.
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From page 113... ...
Tarball formation, like shoreline stranding, is ranked highest for releases of crudes and heavy oils that form persistent residues. Seeps Crude oil released into the marine environment through natural seepage undergoes most of the same physical and chemical process as crude oil released into the ocean at the seafloor.
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From page 114... ...
Many crudes will emulsify readily, a process that greatly reduces subsequent weather ing rates. As a result, crude oil spills close to shore often strand and persist on shorelines, particularly on permeable substrates such as gravel beaches and sheltered habitats such as marshes.
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From page 115... ...
Unlike the other sources discussed in this report, atmospheric deposition supplies hydrocarbons somewhat uniformly to the coastal ocean at relatively low loading rates over large areas. Analysis of the concentrations of petroleum hydrocarbons in the coastal ocean indicates that the surface waters are greatly oversaturated with n-alkanes with respect to the overlying atmosphere.
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From page 116... ...
Oil entering the marine environment comes from natural sources (oil seeps) and from sources over which humankind has some control (oil spills, urban runoff, pollution resulting from oil transportation and production, and oil usage in ve
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From page 117... ...
Coast Guard, and the USGS, should work with industry to develop and support a systematic and sustained research effort to further basic understanding of the processes that govern the fate and transport of petroleum hydrocarbons released into the marine environment from a variety of sources (not just spills)
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From page 118... ...
inputs from two-stroke recreational vessels are a large marine source of petroleum hydrocarbons. These discharges are primarily gasoline and lube oil, which have high evaporation rates and Tow PAH levels.
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