94 



to those of Santa Monica Bay„ suggesting that the effect of 

 sewage discharge has not appreciably increased the average 

 quantity of organic matter in the bay except near the outfall. 



The distribution and quantity of organic matter in any 

 region depends to a large extent upon the movement and physico- 

 chemical nature of the overlying water, and the balance between 

 organic and inorganic deposition. For example, the main cause 

 for the offshore increase in organic carbon is the change in 

 the texture of the sediments in a seaward direction. This is 

 illustrated in Figure 30 in which per cent organic carbon is 

 plotted against median diameter. The diagram clearly illus- 

 strates that as the grain size of the sediment decreases, the 

 percentage of organic carbon rises. This relationship is so 

 well established that Trask (1939, p„ 434), knowing the type 

 of sediment, has utilized empirical constants in order to make 

 rough determinations of the percentage of organic matter in 

 the sediment, 



Detrital sediments and organic debris having the same 

 densities will accvimulate together. In the regions where 

 sands predominate, i.e., in the nearshore zone, currents and 

 turbulence usually are strong enough to wash away fine silt 

 anc clay as well as organic matter which is fine grained and 

 is relatively light, so that it is easily transported by 

 weak currents. Even if large fragments of organic debris 

 were deposited in the nearshore zone, decomposition by 

 oxidation or bacterial action would slowly break down the 

 material into finer and finer particles which would probably 

 be washed seaward and deposited in quieter water. The large 



