Page 106 - Environmental Control in Petroleum Engineering

The Impact of Drilling and Production Operations 93

polyaromatic hydrocarbon concentrations were on the order of 1 ppm.
Reduced fauna concentrations were observed for polyaromatic hydro-
carbon concentrations on the order of 0.1 ppm.
A four-year study was conducted on the ecological effects, chemical
fate, and microbial responses of marsh systems following crude oil
spills (American Petroleum Institute, 198la). The effects of oil spills
on phytoplankton were short lived, with a recovery within seven days
to the levels found in the control area. The effects of oil on standing
marsh plants were severe during the first year following exposure.
Growth during the third year was, on the average, as great as in the
control area, although growth in the high plant concentration areas was
still lower.
The impact of chronic exposure to tar balls on intertidal biota in a
rocky shore community in Bermuda have also been studied (American
Petroleum Institute, 1984a). There was no correlation between the
presence or amount of tar on the shore and the reproductive status of
the six intertidal species studied. Snail size was correlated with the
presence of tar, however. Little accumulation of hydrocarbons in
tissues of intertidal animals was found. Tar balls are believed to come
from discharged tanker ballast tanks, with the level of tar on a beach
being controlled by the amount of direct exposure to constant wave
action, topography, and configuration of the shoreline. Tar balls are
accumulated almost exclusively in the upper intertidal and splash zone.
One important way to gain information about the effects of chronic
exposure of ecosystems to crude oil is to study areas having natural
oil seeps. Studies at natural seeps at Coal Oil Point in the Santa
Barbara Channel, California, have shown that the level of macrofauna
is reduced when the hydrocarbon content in the sediments is high
(National Research Council, 1985; American Petroleum Institute,
1980). The reason for the lower faunal level is the reduced amount
of oxygen, high sulfide content, and high level of dissolved hydro-
carbons (mostly aromatics) in the surrounding water. Aromatic concen-
trations in water have been measured as high as 1.3 mg/1. Areas with
lower seepage (less than 0.1 mg/1) show little or no impact.
A separate study of a major natural seep area near Santa Barbara,
California, that leaks 50-70 barrels of oil per day revealed little
impact. The growth rate of resident marine organisms near the seeps
was not affected, the total biomass (plant and animal life) and biomass
of individual species groups were not related to the presence of