vary accordingly. Collection of samples of a heavy 

 oil slick near the origin of spillage presents no par- 

 ticular difficulty because an adequate quantity may 

 be scooped easily and placed in a proper container. 

 Serious difficulty arises, however, in case of an 

 irridescent film of oil approaching the thickness of 

 a monomolecular layer. Garrett (1964), made a 

 special study of slick-forming materials naturally 

 occurring on sea surfaces and demonstrated their 

 highly complex composition. The collection of 

 very thin layers of surface water was made by 

 means of a specially constructed plastic screen. 

 The entrapped compounds were washed off into 

 a large container (Garrett, 1962). He found sur- 

 face-acting substances in all areas where the sea 

 surface was altered by monomolecular films and 

 concluded that "a chemical potential exists 

 whereby such surface alterations can occur when 

 conditions are suitable for the adsorption and 

 compression of the surface-active molecules at 

 the air/water boundary." The oil film at the 

 air/water boundary may be composed of several 

 interacting organic compounds. This complexity 

 must be kept in mind in studies of oil pollution in 

 sea water. 



If a relatively thick layer of contaminated water 

 is needed, the sample may be scooped or sucked 

 from an area of sea surface enclosed by a floating 

 frame. Interference due to wave ripples is mini- 

 mized in this way. 



For analysis of an oil emulsion in sea water, a 

 sample of a desired volume may be collected by 

 pump or by any type of self-closing water bottle 

 lowered within the surf area. 



For obtaining water soluble substances leached 

 from oil sludge, sampling should be made by 

 pumping or by using a water sampler lowered as 

 close as possible to the oil-covered bottom. 



Samples of oil adsorbed on sediments can be 

 obtained by using bottom samplers designed to 

 take quantitative samples. 



Contamination of beaches by floating tar ballast 

 and cleaning water discharged by ships sailing 

 along our coast is of such common occurrence that 

 at present it is almost impossible to find a pubhc 

 beach free from this nuisance. Cakes of solidified 

 oil tar can be picked by hand from the tidal zone 

 of any beach along the Atlantic and Gulf coasts. 



Recommendation: Until more information on the 

 chemistry and toxicology of oil in sea water becomes 

 available, the following requirements are recommended 

 for the protection of marine life. No oil or petroleum 

 products should be discharged into estuarine or coastal 

 waters in quantities that (1) can be detected as a 

 visible film or sheen, or by odor, (2) cause tainting 

 of fish and/or edible invertebrates, (3) form an oil- 

 sludge deposit on the shores or bottom of the receiving 



body of water, or (4) become effective toxicants ac- 

 cording to the criteria recommended in the "Toxicity" 

 section. 



Turbidity and color 



Turbidity, color, and transparency are closely 

 interrelated phenomena in water. They must be 

 observed simultaneously because transparency is 

 a function of turbidity, water color, and spectral 

 quality of transmitted light. For practical pur- 

 poses, however, it is more convenient to discuss 

 them separately. 



Turbidity 



By observing the turbidity of sea water it is pos- 

 sible to determine the depth of the euphotic zone; 

 i.e., the depth in which organic carbon is produced. 

 Various particles suspended in water reduce the 

 intensity of light by absorption and scattering. In 

 the sea, the maximum depth of growth of attached 

 plants varies. It is 160 m in the Mediterranean, 

 30 m in Puget Sound, and 10 m off Cape Cod. In 

 general, benthic plants will not grow at a depth at 

 which the light intensity is less than 0.3 percent of 

 its surface value (Clarke, 1954). In any environ- 

 ment, the rate of photosynthesis decreases with the 

 attenuation of light but the respiration rate remains 

 approximately the same. Because the role of 

 phytoplankton in organic production is far more 

 important quantitatively than that of benthic 

 plants, an increase in the turbidity of water di- 

 minishes primary productivity of the ocean bio- 

 mass as indicated by the rate of growth of various 

 planktonic algae. 



For each species of plant, a level of light inten- 

 sity may be reached at which the rate of photo- 

 synthesis becomes equal to the rate of respiration. 

 This level is designated as compensation intensity 

 and the depth at which this value is found is called 

 the compensation depth. For marine phytoplank- 

 ton, it has been determined that compensation in- 

 tensity is about 100 ft-candles, or 1 percent of the 

 value of full sunlight (Clarke, 1954). In natural 

 waters, the compensation depth varies; e.g., in the 

 Gulf of Maine it was found to be 30 m while at 

 Woods Hole only 7 m. 



In many coastal waters, the principal cause of 

 turbidity is the discharge of silt carried out by the 

 principal rivers. Secchi disc readings show that the 

 transparency of water at the mouths of large rivers 

 during flood stage may be reduced to a few centi- 

 meters. At normal river stages, the disc may be 

 visible at several meters below the surface. Ob- 

 servations from an airplane are useful in recording 



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