Page 104 - Environmental Control in Petroleum Engineering

The Impact of Drilling and Production Operations SI

and thermal insulation. The birds then sink and drown or die of
hypothermia. Oil can also be ingested by the birds during preening
of oiled plumage. Although this oil becomes distributed throughout the
body, there is no evidence that ingested oil is a primary cause of death
among birds (National Research Council, 1985).
Nonlethal exposures of birds to crude oil significantly reduces
hatchling success and fledgling success in a dose-dependent manner
(American Petroleum Institute, 1988). Adult petrels were most sensit-
ive to contaminant exposure late in the incubation period and early
in the post-hatchling period. Pollutant-related decreases in reproductive
success were probably associated with temporary abandonment of the
nesting burrow by adults. Treated adults generally returned to normal
behavior in the second season following exposure. The primary con-
cern for marine birds appears to be the immediate effects on adult
mortality and the resulting population dynamics. The effects of sublethai
exposures may be significant only in areas where exposure is chronic,
Crude oil also impacts phytoplankton and zooplankton. The effect
of crude oil is to inhibit growth and photosynthesis (for phytoplank–
ton) at concentrations in the range of 1-10 mg/1 (National Research
Council, 1985).
The effect of oil on marine mammals is highly variable. Fur-
insulated mammals lose their ability to thermally regulate their tem-
perature as their oil-contaminated fur loses its insulating capacity. The
loss of thermal insulation creates a higher metabolic activity to regulate
body temperature, which results in fat and muscular energy reserves
being rapidly exhausted. This can result in the animal's death by
hypothermia or drowning. Many species show no avoidance response
to oiled areas. Chronic contact of marine mammals with oil may also
result in skin and eye lesions (National Research Council, 1985).

Impact of Crude Oil on Ecosystems

Only a few studies have been conducted on the chronic effects of
hydrocarbon releases on ecosystems. No apparent long-term impacts
on the productivity of ecosystems have been observed. In all cases,
the affected areas recovered after the hydrocarbon source had been
removed, although full recovery could take a number of years. One
difficulty with ecosystem studies, however, is that little is known about
ecosystems that have not been exposed to hydrocarbons. This makes