The quality of the phytoplankton population developed under different environ- 

 mental conditions is, however, not yet well understood. Even under natural condi- 

 tions, the species composition changes seasonally. Temperature is an important 

 determinant of these changes. The addition of pollution can also change the normal 

 species distribution of the phytoplankton population. This is commonly observed in 

 heavily polluted inshore waters. Frequently, the species that grow best under pol- 

 luted conditions, and consequently dominate the population, are not desirable as 

 food for higher trophic levels. Pollution is not a"balanced"fertilizerfor phytoplank- 

 ton requirements since it is generally deficient in nitrogen relative to phosphorus. The 

 effect of variable ratios of essential elements on the species composition of natural 

 phytoplankton populations is just beginning to be understood, and much more study 

 will be required before definite conclusions concerning the effect can be reached. 



The distribution of a conservative element within an estuary can be evaluated or 

 predicted readily for steady-state conditions as illustrated for the Hudson Estuary. 

 The details of the distribution, and particularly the mechanisms that control and 

 produce the observed distributions, are more difficult to understand and predict. 

 More sophisticated models are necessary for this purpose. They are particularly 

 valuable to evaluate transient events and to assess the effects of biological or other 

 time-variable processes in producing the observed distributions. It is gratifying that 

 progress is being made to achieve an understanding of these problems, but much 

 remains to be done. 



In conclusion, it seems appropriate to make use of the assimilative capacity of 

 marine coastal waters for the disposal of the wastes of human metabolism. This can 

 be done properly only by making the best use of scientific understanding of the entire 

 system, including the biological, physical, and chemical characteristics. Mistakes 

 have been made in the past, partly because the system as a whole was not adequately 

 understood. Today, there is no excuse to repeat the mistakes of the past, and it 

 should be possible to design disposal operations to achieve the maximum benefit 

 without detrimental effects. 



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