the open ocean at high latitudes and in the winter 

 when phytoplankton density is low, the fraction of 

 inorganic phosphorus may increase to 0.65 or 

 thereabout. 



Recommendation: The ecological factors most often 

 associated with nuisance growths are changes in the 

 natural temperature and salinity cycles and increases 

 in nutrients. The change in any of these factors may 

 directly or indirectly affect the response of the orga- 

 nisms to other factors. Increase or decrease in current 

 and, indirectly, its effect on available nutritional ma- 

 terials have also been found to be important. 



To maintain a balance among nutrients and a bal- 

 anced biota most conducive to the production of a 

 desired crop, it is recommended that: 



(1) No changes should be made in the basin geom- 

 etry, current structure, salinity, or temperature of the 

 estuary without first studying the effects on aquatic life. 

 For example, these studies should be made before dams 

 are erected, water diversion projects are constructed, 

 or dredge and fill operations carried out. 



(2) The artificial enrichment of the marine en- 

 vironment from all sources should not cause any major 

 quantitative or qualitative alteration in the flora. Pro- 

 duction of persistant blooms of phytoplankton, whether 

 toxic or not, dense growths of attached algae or higher 

 aquatics or any other sort of nuisance that can be 

 directly attributed to nutrient excess or imbalance 

 should be avoided. Because these nutrients often are 

 derived largely from drainage from land, special atten- 

 tion should be given to correct land management in a 

 river basin and on the shores of a bay to prevent ero- 

 sion. 



(3) The naturally occurring atomic ratio of NO:i-N 

 to PO.-P in a body of water should be maintained. 

 Similarly, the ratio of inorganic phosphorus (ortho- 

 phosphate) to total phosphorus (the sum of inorganic 

 phosphorus, dissolved organic phosphorus, and par- 

 ticulate phosphorus) should be maintained as it occurs 

 naturally. Imbalances have been shown to bring about 

 a change in the natural diversity of the desirable orga- 

 nisms and to reduce productivity. 



Toxic Substances 



Relatively few of the many substances recog- 

 nized as potential toxic pollutants of the marine 

 environment have been studied sufficiently to en- 

 able us to define their maximum allowable concen- 

 trations. Specific pollutants and classes of pollu- 

 tants are discussed in terms of current knowledge. 

 In some cases, data are adequate to set definite 

 criteria, while in others, criteria are educated 

 guesses at best and can serve only as temporary 

 guidelines. 



Lethal concentrations of some persistent sub- 

 stances as determined by acute toxicity tests are 

 so low that we are not justified in allowing their 

 deliberate introduction into the natural environ- 

 ment. On the other hand, a few waste products 

 appear to offer little threat to the marine environ- 



ment because of their rapid degradation and 

 dispersal. 



Our concern is not primarily with what polluting 

 substances are present, but whether or not they are 

 present in sufficiendy large amounts to cause dele- 

 terious effects on the biota and the environment. 

 Many naturally occurring substances, including 

 clean fresh water, would be toxic if discharged into 

 the estuarine and coastal marine environment in 

 sufficiently large amounts. 



Determination of the toxicity of known and un- 

 known effluents, either simple or complex mix- 

 tures, can best be made by determining the reac- 

 tions of endemic fauna exposed to them at levels 

 that might be expected in receiving waters. Chemi- 

 cal assays may determine the presence of such pol- 

 lutants at levels as low as nanograms per liter, but 

 biological systems may be affected by even smaller 

 amounts. Many animals have the ability to accu- 

 mulate toxic residues of substances present in the 

 environment in only trace amounts until body resi- 

 dues are large enough to cause damage when re- 

 leased internally through normal metabolic proc- 

 esses. Animals differ in their sensitivity to the same 

 toxicant and it is essential that toxicity data be 

 related, in the final analysis, to animals of eco- 

 nomic importance. 



A fundamental concept in attacking the pollu- 

 tion problem is the assumption that effluents con- 

 taining foreign materials are harmful and not per- 

 missible until laboratory tests have shown the 

 reverse to be true. It is the obligation of the agency 

 producing the effluent to demonstrate that it is 

 harmless rather than require pollution abatement 

 agencies to demonstrate that the effluent is causing 

 damage. 



Specific methods are suggested here for the 

 determination of the toxicity of proposed effluents. 

 While certain procedures are desirable, they are 

 not always reasonable and certain permissible 

 alternatives are also given. 



Basic Bioassay Test: The basic bioassay test 

 shall consist of a 96-hour exposure of an appro- 

 priate organism, in numbers adequate to assure 

 statistical validity, to an array of concentrations of 

 the substance, or mixture of substances, that will 

 reveal the level of pollution that will cause ( 1 ) ir- 

 reversible damage to 50 percent of the test orga- 

 nisms, and (2) the maximum concentration caus- 

 ing no apparent effect on the test organisms in 

 96 hours. Tests should be conducted, when pos- 

 sible, in a "flow-through" system so that the or- 

 ganisms are exposed continuously to a fresh 

 solution of the test material appropriately diluted 

 with water of the same quality as that at the site 

 of the proposed discharge. Adequate safeguards 



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