52
2.4.2 Sensing and Tracking Petroleum Pollution in the Marine
Environment
Chemical Composition, Weathering, and Effects of Petroleum Pollution
Petroleum is a complex mixture of hydrocarbons that may be naturally released into
the marine environment through sediment and coastal seeps. However, involuntary
spills incurred during oil and gas exploration, and their transport and use, have
vastly increased the volume of petroleum and its products entering marine water.
Crude petroleum and its refined products are generally lighter than water, although
a few heavier bitumen nonfloating oils may have a greater density than seawater
(1.02–1.03 g.cm
−3
) and will sink when released upon the ocean surface. Petroleum
hydrocarbons are largely insoluble in water exhibiting bulk mass fractions ranging
from well below a few micrograms per kg.
Most petroleum seeps and spills initially make their way to or remain on the
surface creating slicks and subsequently undergo physical, chemical, and biological
weathering changes that promote evaporation, dissolution, dispersion, entrainment
of mineral particulates, and microbial degradation. Initial weathering losses are due
to evaporation of the lighter fractions and moderate dissolution of the more soluble
fractions. Extended weathering in moderate climatic conditions leads to the formation of tar balls which may eventually sink with the loss of lighter fractions and the
added weight of biofouling organisms. High seas and winds on the other hand promote the formation of a persistent oil/water emulsion known as mousse (due to its
similarity to the chocolate dessert).
Petroleum brings about decreased biological function, and death in the extreme,
through various physical and chemical processes. Bird feathers and mammal pelts
coated with oil lose their insulating properties leading in extreme to death from
hypothermia. Aromatic hydrocarbons, the most soluble (or rather least insoluble)
fraction of crude petroleum, and light derivatives such as gasoline are both toxic and
mutagenic. Petroleum spills reaching the coastal zone lead to particularly adverse
consequences to productive ecosystems such as marshes, mangroves, oyster beds,
seagrass beds, and coral reefs. Persistence of petroleum that finds its way into these
environments is shortened in environments subject to high wave energy (Evans
et al. 2017) but can extend to decades in low energy environments such as mangrove
ecosystems (Corredor et al. 1990). Further reference to inputs, fate, and effects of oil
in the sea is available in two comprehensive consensus study reports of the US
National Research Council (National Research Council 1985; Transportation
Research Board and National Research Council 2003).
Oil spill response depends on timely identification for containment and treatment
or, preferentially, removal. Since oil rapidly disperses in thin slicks upon the ocean
surface, rapid confinement is of essence. For the reasons discussed above, however,
regulatory agencies may prescribe dispersion of the product throughout the water
column using chemically formulated dispersant to prevent spills from reaching the
especially vulnerable coastal zone. This dispersion can affect planktonic organism
due to toxicity of the aromatic fraction. Moreover, the dispersants currently available are themselves toxic, compounding the effects on planktonic communities.
2 Electronic Sensors and Instruments for Coastal Ocean Observing
2.4.2 Sensing and Tracking Petroleum Pollution in the Marine
Environment
Chemical Composition, Weathering, and Effects of Petroleum Pollution
Petroleum is a complex mixture of hydrocarbons that may be naturally released into
the marine environment through sediment and coastal seeps. However, involuntary
spills incurred during oil and gas exploration, and their transport and use, have
vastly increased the volume of petroleum and its products entering marine water.
Crude petroleum and its refined products are generally lighter than water, although
a few heavier bitumen nonfloating oils may have a greater density than seawater
(1.02–1.03 g.cm
−3
) and will sink when released upon the ocean surface. Petroleum
hydrocarbons are largely insoluble in water exhibiting bulk mass fractions ranging
from well below a few micrograms per kg.
Most petroleum seeps and spills initially make their way to or remain on the
surface creating slicks and subsequently undergo physical, chemical, and biological
weathering changes that promote evaporation, dissolution, dispersion, entrainment
of mineral particulates, and microbial degradation. Initial weathering losses are due
to evaporation of the lighter fractions and moderate dissolution of the more soluble
fractions. Extended weathering in moderate climatic conditions leads to the formation of tar balls which may eventually sink with the loss of lighter fractions and the
added weight of biofouling organisms. High seas and winds on the other hand promote the formation of a persistent oil/water emulsion known as mousse (due to its
similarity to the chocolate dessert).
Petroleum brings about decreased biological function, and death in the extreme,
through various physical and chemical processes. Bird feathers and mammal pelts
coated with oil lose their insulating properties leading in extreme to death from
hypothermia. Aromatic hydrocarbons, the most soluble (or rather least insoluble)
fraction of crude petroleum, and light derivatives such as gasoline are both toxic and
mutagenic. Petroleum spills reaching the coastal zone lead to particularly adverse
consequences to productive ecosystems such as marshes, mangroves, oyster beds,
seagrass beds, and coral reefs. Persistence of petroleum that finds its way into these
environments is shortened in environments subject to high wave energy (Evans
et al. 2017) but can extend to decades in low energy environments such as mangrove
ecosystems (Corredor et al. 1990). Further reference to inputs, fate, and effects of oil
in the sea is available in two comprehensive consensus study reports of the US
National Research Council (National Research Council 1985; Transportation
Research Board and National Research Council 2003).
Oil spill response depends on timely identification for containment and treatment
or, preferentially, removal. Since oil rapidly disperses in thin slicks upon the ocean
surface, rapid confinement is of essence. For the reasons discussed above, however,
regulatory agencies may prescribe dispersion of the product throughout the water
column using chemically formulated dispersant to prevent spills from reaching the
especially vulnerable coastal zone. This dispersion can affect planktonic organism
due to toxicity of the aromatic fraction. Moreover, the dispersants currently available are themselves toxic, compounding the effects on planktonic communities.
2 Electronic Sensors and Instruments for Coastal Ocean Observing