THE PROBLEM OF OIL POLLUTION O F THE SEA
239
clean is one of large pebbles, between which oil may sink to a depth
of 0.5-1 m (see Wardley Smith, 1968a). Oil does not sink so readily
into wet sand, but breakers may throw fresh sand over it, burying it
in layers like geological strata (Fig. 13, p. 276). I n this way a badlypolluted beach may appear clean shortly after the stranding of the oil,
which is revealed later by the removal of surface layers during storms
or in seasonal sand-movements (ZoBell, 1959, 1964; Smith, 1968;
Kolpack, 1969).
Oil may also persist on dry rock surfaces or amongst weed, barnacles
and mussels, where in addition to the biological agencies discussed
below it is slowly removed by drying, hardening and the incorporation
of sand particles, finally eroding or flaking off. Although they fail to
wet the mucous body surfaces of animals or the mucilaginous surface of
lower-shore algae, some oils cling to the byssus-threads of mussels, the
horny outer layer of shells and upper-shore weeds which have a naturally
oily surface. At the head of the shore, oil also has an affinity for some
maritime grasses and flowering plants, which have been used in the
mopping-up of localized spills.
Tide-pools become covered with a thick film of oil, but this has a
surprisingly small influence on gas-exchange across the surface.
Roberts (1926) showed that during a 24-h test period, water depleted
of oxygen by boiling reached 99% saturation below a film of diesel
oil 0.002 mm thick and 60% saturation below an 0.03 mm layer.
Boswell (1950) found that a layer of crude oil 0.5 mm thick reduced
the rate at which boiled sea water absorbed oxygen to 85% of his
uncovered control during a six-day test. Brown and Reid (1951), in
similar experiments over a two-day period, found that in some tests
a 1.4mm layer had no detectable effect; at worst, the amount of
oxygen absorbed through the oil was 75% of that taken up by the control sample. Water beneath a 17 mm layer absorbed 73% as much as
the control. During the pollution of the Santa Barbara Channel by a
ieaking off-shore oil-well, the oxygen saturation beneath a " heavy
slick " (thickness not specified) was 98.5% of that in clear water nearby.
However, light intensities beneath the oil, measured on two occasions,
were generally 1% of surface intensity and at best 5-10% (Smithsonian
Institution, 1969b). This attenuation is likely to be unimportant beneath a moving oil-slick at sea but may have greater effects in rockpools which, on a sunny day, are normally supersaturated with oxygen
from the photosynthetic activity of the algae growing in them. It
seems probable that a layer of dark-coloured oil would also raise the
water temperature by its absorption of solar energy and by blanketing
the surface of the pool, but measurements or estimates of the magnitude
239
clean is one of large pebbles, between which oil may sink to a depth
of 0.5-1 m (see Wardley Smith, 1968a). Oil does not sink so readily
into wet sand, but breakers may throw fresh sand over it, burying it
in layers like geological strata (Fig. 13, p. 276). I n this way a badlypolluted beach may appear clean shortly after the stranding of the oil,
which is revealed later by the removal of surface layers during storms
or in seasonal sand-movements (ZoBell, 1959, 1964; Smith, 1968;
Kolpack, 1969).
Oil may also persist on dry rock surfaces or amongst weed, barnacles
and mussels, where in addition to the biological agencies discussed
below it is slowly removed by drying, hardening and the incorporation
of sand particles, finally eroding or flaking off. Although they fail to
wet the mucous body surfaces of animals or the mucilaginous surface of
lower-shore algae, some oils cling to the byssus-threads of mussels, the
horny outer layer of shells and upper-shore weeds which have a naturally
oily surface. At the head of the shore, oil also has an affinity for some
maritime grasses and flowering plants, which have been used in the
mopping-up of localized spills.
Tide-pools become covered with a thick film of oil, but this has a
surprisingly small influence on gas-exchange across the surface.
Roberts (1926) showed that during a 24-h test period, water depleted
of oxygen by boiling reached 99% saturation below a film of diesel
oil 0.002 mm thick and 60% saturation below an 0.03 mm layer.
Boswell (1950) found that a layer of crude oil 0.5 mm thick reduced
the rate at which boiled sea water absorbed oxygen to 85% of his
uncovered control during a six-day test. Brown and Reid (1951), in
similar experiments over a two-day period, found that in some tests
a 1.4mm layer had no detectable effect; at worst, the amount of
oxygen absorbed through the oil was 75% of that taken up by the control sample. Water beneath a 17 mm layer absorbed 73% as much as
the control. During the pollution of the Santa Barbara Channel by a
ieaking off-shore oil-well, the oxygen saturation beneath a " heavy
slick " (thickness not specified) was 98.5% of that in clear water nearby.
However, light intensities beneath the oil, measured on two occasions,
were generally 1% of surface intensity and at best 5-10% (Smithsonian
Institution, 1969b). This attenuation is likely to be unimportant beneath a moving oil-slick at sea but may have greater effects in rockpools which, on a sunny day, are normally supersaturated with oxygen
from the photosynthetic activity of the algae growing in them. It
seems probable that a layer of dark-coloured oil would also raise the
water temperature by its absorption of solar energy and by blanketing
the surface of the pool, but measurements or estimates of the magnitude