MAN'S IMPACT ON THE COASTAL ENVIRONMENT: 

 NUTRIENTS IN THE MARINE ENVIRONMENT 



by 



Bostwick H. Ketchum 



Woods Hole Oceanographic Institute 

 Woods Hole, Massachusetts 02543 



INTRODUCTION 



The waste of human metabolism is rich in organic matter and in the fertilizing 

 nutrients essential for plant growth. Civilized people dilute this potentially valuable 

 natural resource with excessive volumes of carefully purified drinking water, add a 

 witch's brew of toxic chemicals, collect the resultant mixture from large areas of 

 densely populated land to concentrate it in one small location for disposal, and then 

 complain bitterly that it is expensive, if not impossible, to discharge the product into 

 the environment without damage to the ecosystem. For over a century the hazards 

 posed to public health by sewage have been recognized, and it is sterilized to prevent 

 the spread of waterborne disease. It was also early recognized that this mixture con- 

 tained large amounts of organic matter and that excessive discharge into an isolated 

 part of the aquatic environment would remove all available oxygen from the water 

 and lead to putrefaction and the production of hydrogen sulfide with its obnoxious 

 odor. Treatment plants were built to solve these two problems. The sewage was sep- 

 arated into a relatively clear though not drinkable effluent and a watery quasi-solid 

 containing much of the particulate organic material and a major share of the toxic 

 materials that were added in the collection system. In this way, two disposal prob- 

 lems were created in place of one. 



In retrospect, it appears that little has been accomplished that is admirable or 

 desirable, though it is obvious that modern cities could not exist without their sewers. 

 Today it is known that the apparently clear and innocuous effluent contains most of 

 the elements essential for plant growth that were in the original mixture. This ef- 

 fluent is a biostimulant or fertilizer, and when this is added to the aquatic environ- 

 ment, the natural plant populations quickly produce about the same amount of 

 organic material as that which was removed at great expense in the treatment plant. 

 The semisolid sludge, which contains most of the organic material present in the 

 original mixture, could be used as a soil conditioner and fertilizer except that the 

 excessive toxics it contains make this disposal option impractical. 



Thus the human population finds itself in a dilemma. Efforts to solve one set of 

 problems have created other problems that are at least as serious. These problems are 

 not confined to any one country; they are global in extent and are found wherever 

 people gather together into densely populated urban areas. If the human popula- 

 tion were spread uniformly over the entire habitable area of earth, there would be 

 little problem. For large areas, the "night-soil" would increase agricultural produc- 

 tion, albeit with the hazard of disease propagation. For more fastidious people, on- 

 site disposal is practical so long as each family unit is far enough removed from its 

 neighbors. Obviously, demands of modern civilization make this option impractical. 



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