Oiled
coast in Galicia. Also below, centre. Photo: ©
Pablo, La Marea Negra. Cleanup of heavily oiled
beach, Wales. Photo: © University
of Wales Swansea. Impacted marsh at low tide
in Arcata Bay, U.S. Photo: © NOAA.
Trunks of mangrove trees blackened by oil. Photo:
© NOAA.
Heavily oiled section of beach, Herring Bay, Prince
William Sound. Photo: ©
NOAA.
SENSITIVITY
OF COASTAL ENVIRONMENTS TO OIL
The U.S. Coastguard have listed
shoreline types, from the least (low figures)
to the most sensitive ones to oil pollution:
- Exposed
rocky cliffs and seawalls
- Wave
cut rocky platforms
- Fine
to medium-grained sand beaches
- Coarse-grained
sand beaches
- Mixed
sand and gravel beaches
- Gravel
beaches/Riprap
- Exposed
tidal flats
- Sheltered
rocky shores/man-made structures
- Sheltered
tidal flats
- Marshes
It should be noted that other shore types and
shallow underwater habitats are also very sensitive
to oil pollution, including:
- Mangroves
(And according to ITOPF: "Leaving residual
oil to weather and degrade naturally is usually
recommended for sensitive shoreline types such
as salt marshes and mangroves, because they
have been shown to be more easily damaged by
the physical disturbance caused by clean-up
teams and vehicles than by the oil itself. If
any cleaning is attempted, it should be carried
out with specialist guidance and advice.")
- Coral
reefs See also NOAA.
EFFECTS
Spilled
oil and certain cleanup operations can threaten
different types of marine habitats in different
ways.
Coral reefs are important nurseries for
shrimp, fish, and other animals as well as recreational
attractions for divers. Coral reefs and the marine
organisms that live within and around the reefs
are at risk from exposure to the toxic substances
within oil as well as smothering.
Exposed sandy, gravel or cobbled beaches
are usually cleaned by manual techniques. Although
oil can soak into sand and gravel, few organisms
live full-time in this habitat, so the risk to
animal life or the food chain is less than in
other habitats, such as tidal flats.
Sheltered beaches have very little wave
action to encourage natural dispersion. If timely
cleanup efforts are not begun, oil may remain
stranded on these beaches for years.
Tidal flats are broad, low-tide zones,
usually containing rich plant, animal, and bird
communities. Deposited oil may seep into the muddy
bottoms of these flats, creating potentially harmful
effects on the ecology of the area.
Salt marshes are found in sheltered waters
in cold and temperate areas. They host a variety
of plant, bird,and mammal life. marsh vegetation,
especially root systems, is easily damaged by
fresh light oils.
Mangrove forests are located in tropical
regions and are home to a diversity of plant and
animal life. Mangrove trees have long roots, called
prop roots, that stick out well above the water
level and help to hold the mangrove tree in place.
A coating of oil on these prop roots can be fatal
to the mangrove tree, and because they grow so
slowly, replacing a mangrove tree can take decades.
Sea-bottoms. Oil contamination of the seabed
may cause serious long- and short term effects
on bottom-dwelling organisms (animals, algae and
microorganisms). Filtering organisms such as oysters
and mussels and clams which filters large volumes
of water to get their food are especially likely
to accumulate oil or oil components. In addition,
if tar-like clumps of oil sink to the bottom,
they may destroy living conditions for bottom-living
organisms, as well as nursing grounds for fish
and shellfish.
At low temperatures, oil tends to persist
for long periods because of the low rates of evaporation.
The frozen ground prevents it from seeping in,
and this has the effect of making it travel for
long distances. Disturbance of the thin layer
of vegetation covering a frozen soil can precipitate
catastrophic meeting of the underlying ice and
result in extensive thermokarst erosion. Tundra
environments are particularly susceptible to disturbance,
and effects remain visible for many years. Many
of the Arctic plants are very susceptible to pollutants,
especially lichens which are the main food of
reindeer.
RECOVERY
The negative effects of on oil spill may eventually
fade away, but in many cases it will be matter
of several years, even decades, before an area
or ecosystem has fully recovered from a spill
that caused extensive damages. Every situation
is unique and depending on the particular conditions
and circumstances in that area, and on the characteristics
of the spill. Some areas might recover in a matter
of weeks, others will need up to 20 years.
The recovery of the affected habitats and species
following an oil spill will to a large extent
depend on the type of ecosystem , the vulnerability
of the species and not least the climate of the
region where the oil spill occurs. Generally,
recovery will proceed faster in warmer climates
and on rocky shores compared to cold climates
and, for example, marshes. The long-term effects
on deeper bottoms (i.e., if oil sinks and is absorbed
in bottom sediments) is also a matter of concern.
The best documented evidence concerning the recovery
of ecosystems affected by massive oil pollution
are from the Persian Gulf and resulting from the
discharges associated with the Gulf War in 1991.
Studies (GESAMP) suggest
that the chronic and acute releases that took
place were rather rapidly accommodated by the
system. Already at the end of 1992, researchers
reported that many of the worst hit beaches in
Saudi Arabia were almost clean of oil. It is believed
that this may have been the result of the warm
water of the Gulf and the fact that its bacterial
populations were able to degrade and weather the
oil much more quickly than previously believed
to be possible.
The experience gained from the Exxon Valdez
spill has been documented, and could serve as
one example of what happens in the aftermath of
a major spill in a sensitive area. See, for example,
the web site of the Exxon
Valdez Oil Spill Trustee Council, and NOAA
Office of Response and Restoration ("NOAA
biologists have been monitoring the long-term
effects of the spill and cleanup efforts. Here
are some of their reports, along with links to
more information elsewhere").
The economic recovery of an area will depend on
the possibilities to regain the confidence of
the consumers for marine products from the region
and convince the tourists that the area is once
more clean and as attractive as ever before. Intense
marketing campaigns (possibly financed by some
of the money paid as compensation) might be important
in such endeavours.
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