the distribution of brackish, silt-laden waters along 

 the coast. Silting of the estuaries and adjacent 

 coastal water should be considered as a special 

 case of pollution resulting from deforestation, 

 overgrazing and faulty agricultural practices, road 

 construction, and other land management abuses. 



Mixed efHuents from various industrial plants 

 and domestic sewage increase the turbidity of 

 receiving water. It is difficult to distinguish be- 

 tween the effect of the attenuation of light due to 

 suspended particles and the direct effect of the 

 particles in suspension on the growth and physi- 

 ology of aquatic organisms. Natural silt taken 

 from the bottom of the sea and kaolin affect the 

 development of eggs and the growth of larvae of 

 oysters and hard shell clams {Mercenaria merce- 

 naria). In a suspension of 2 g of dry silt in a liter 

 of sea water, only 39 percent of oyster larvae com- 

 pleted development. In 3 g per liter there was no 

 development (Loosanoff, 1962). Growth of 

 Mercenaria clams was retarded in the concentra- 

 tion of 1 to 2 g/1, but appeared to be normal at 

 0.75 g/1. Development was completely suppressed 

 in the concentration of silt from 3 to 4 g/1 (Davis, 

 1960). Silt concentration of 0.1 g/1 caused a 57- 

 percent decrease in the water transport of an adult 

 oyster. In 4 g/1, the depression was 94 percent 

 (Loosanoff, 1962). The turbidity used in these 

 experiments probably is equivalent to 750 to 

 4,000 mg/1 of turbidity standards, although direct 

 comparison of figures cannot be made accurately. 



The principal significance of turbidity observa- 

 tions in a study of pollution is the determination of 

 the depth of the euphotic zone as a factor affecting 

 primary productivity of the sea (Ryther, 1963). 

 Determination of the coefficient "k" defined as the 

 natural logarithm of the fraction of incident light 

 penetrating to a given depth is of great importance 

 in studies of organic production. In the temperate 

 and northern parts of the ocean, values of "k" 

 range between 0.10 to 0.20 and correspond to 

 depths of 50 to 25 m. In more turbid coastal 

 waters, the coefficient of extinction is as high as 

 1.0 and a compensation depth of 5 m is com- 

 monly encountered. These values may be used as 

 a basis for comparing the characteristics of uncon- 

 taminated waters with those of highly turbid and 

 polluted waters of coastal and inshore areas. A 

 considerable part of the turbidity of these areas is 

 attributable to nonliving particles. 



It must remembered, also, that very high tur- 

 bidity of sea water may be due entirely to blooms 

 such as are known to occur in red tide areas 

 (Galtsoff, 1949) or as a result of unbalanced over- 

 fertilization such as is induced by organic wastes 

 from duck farms in Great South Bay, N.Y. Tur- 



bidity may be determined practically by use of a 

 Secchi disc. Turbidity may be determined more 

 accurately by using the techniques described in 

 Standard Methods for the Examination of Water 

 and Wastewater, 12th edition (1965). Any tur- 

 bidity of less than 1 m (by Secchi disc) or in cor- 

 responding Jackson units should be regarded with 

 suspicion and the nature of suspended material as 

 well as the composition of plankton determined. 



Color 



The color of sea water, expressed as dominant 

 wave length in millimicrons (m/x) covers the 

 range from violet (400 to 465 vafj.) to red-purple 

 (530 to 700 m/t). Spectrophotometric methods, as 

 described in Standard Methods for the Examina- 

 tion of Water and Wastewater, 12th edition 

 (1965), should be used if careful study is re- 

 quired, particularly for determining the exact color 

 of water contaminated with industrial wastes. 



Monitoring the color changes of sea water yields 

 information on the extent of intrusion of fresh 

 water into the sea, the intensity and extent of silt- 

 ing, the location and extent of plankton blooms, 

 the extent and distribution of pollution from indus- 

 trial waste effluents, and the presence and probable 

 thickness of oil film. 



In brackish waters, the blue hue of the open sea 

 is replaced by a greenish or yellowish color. Silting 

 areas are recognizable by brown or yellowish dis- 

 coloration. Red-brownish color is typical of the 

 red tide caused by Gymnodinium and other spe- 

 cies of dinoflageUates. Some of these are toxic to 

 fishes and benthic invertebrates (Galtsoff, 1948, 

 1949). Mass production of forms such as the blue- 

 green alga Trichodesmium gives the surface of the 

 sea an appearance of "green meadow" as described 

 for the Azov Sea by Knipowich (Galtsoff, 1949). 

 Swarming of Phaeocystis pouched, P. globosa, and 

 Rhizosolenia have been reported to extend over 

 hundreds of square miles of the open sea causing 

 a distinct brownish discoloration. 



Systematic studies have not been made yet to 

 determine the optical characteristics of discolored 

 sea water. It is reasonable to expect that such an 

 investigation would be valuable in explaining the 

 cause of discoloration and, in certain instances, 

 may indicate the presence and nature of pollution. 

 Light components specific for the contaminant 

 entering sea water may be detected by the use of 

 a spectrophotometer or with the recording SPOT 

 spectroradiometer recently developed by Alfred C. 

 Konrad of the Massachusetts Institute of Tech- 

 nology. This type of instrument is being used at 

 present at the Woods Hole Oceanographic Institu- 



75 



