ply October through June. The rate of tempera- 

 ture change should not exceed 1 F per hour except 

 when due to natural phenomena. 



Suggested temperatures are to prevail outside 

 of established mixing zones as discussed in the 

 section on zones of passage. 



Dissolved Oxygen 



Oxygen levels sufficient for the survival, growth, 

 reproduction, general well-being, and production 

 of a suitable crop must be maintained. The dis- 

 solved oxygen concentrations necessary to attain 

 this objective in coastal waters, estuaries, and tidal 

 tributaries are: 



( 1 ) Dissolved oxygen concentrations in surface 

 coastal waters should be greater than 5-0 mg/1 

 except when upwellings and other natural pheno- 

 mena may cause this value to be depressed. 



(2) Dissolved oxygen concentration in estu- 

 aries and tidal tributaries should not be less than 

 4.0 mg/1 at any time or place except in naturally 

 dystrophic waters or where natural conditions 

 cause DO to be depressed. 



No oil or petroleum products should be dis- 

 charged into estuarine or coastal waters in quanti- 

 ties that: (1) Can be detected as a visible film, 

 sheen, or by odor; (2) cause tainting of fish or 

 edible invertebrates; (3) form an oil sludge de- 

 posit on the shores or bottom of the receiving body 

 of water; (4) become effective toxicants according 

 to the criteria recommended in the "Toxicity" 

 section. 



Turbidity 



No effluent that may cause changes in turbidity 

 or color should be allowed to enter estuarine or 

 coastal waters unless it can be shown to have no 

 deleterious effects on the aquatic biota. 



Settieabie and Floating Substances 



No materials that contain settieabie solids or 

 substances that may precipitate out in quantities 

 that adversely affect the biota should be introduced 

 into coastal or estuarine waters. It is especially 

 urgent that areas which serve as habitat or nursery 

 grounds for commercially important species be 

 protected from any impairment of natural 

 conditions. 



Tainting Substances 



Substances that taint or produce off-flavors in 

 fish and edible invertebrates should not be pres- 

 ent in concentrations discernible by bioassay or 

 organoleptic tests. 



Radionuclides 



The recommendations made for freshwater or- 

 ganisms apply to marine and estuarine organisms. 



Plant Nutrients and Nuisance Organisms 



(1) No changes should be made in the basin 

 geometry, current structure, salinity, or tempera- 

 ture of the estuary until studies have shown that 

 these changes will not adversely affect the biota or 

 promote the increase of nuisance organisms. 



(2) The artificial enrichment of the marine en- 

 vironment from all sources should not cause any 

 major quantitative or qualitative alteration in the 

 flora such as the production 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 attributed 

 directly to nutrient excess or imbalance. Because 

 these nutrients often are derived largely from 

 drainage from land, special attention should be 

 given to correct land management in river basins 

 and shores of embayments to control unavoidable 

 erosion. 



(3) The naturally occurring atomic ratio of 

 NO3-N to PO4-P in a body of water should be 

 maintained. Similarly, the ratio of inorganic phos- 

 phorus (orthophosphate) to total phosphorus (the 

 sum of inorganic phosphorus, dissolved organic 

 phosphorus, and particulate phosphorus) should 

 be maintained as it occurs naturally. Nutrient im- 

 balances have been shown to cause a change in the 

 natural diversity of desirable organisms and to 

 reduce productivity. 



Toxic Substances 



( 1 ) Substances of Unknown Toxicity: All efflu- 

 ents containing foreign materials should be con- 

 sidered harmful and not permissible until bioassay 

 tests have shown otherwise. It should be the obli- 

 gation of the agency producing the effluent to dem- 

 onstrate that it is harmless in the concentrations 

 that will be found in the receiving waters. All bio- 

 assays should be conducted strictly as recom- 

 mended in the body of this report and the appro- 

 priate application factor applied to determine the 

 permissible concentration of toxicant. 



(2) Pesticides for Which Limits Have Been 

 Determined: The pesticides are grouped according 

 to their relative toxicity to shrimp. Criteria are 

 based on the best estimates in the light of present 

 knowledge and it is to be expected that acceptable 

 levels of toxic materials may be changed as a result 

 of future research. 



36 



