Temperature 



The relationships of temperature and aquatic 

 life have been well studied. Extensive bibliogra- 

 phies and detailed surveys of the subject have been 

 published by the American Society of Civil Engi- 

 neers (1967), Brett (1960), Mlhursky and Ken- 

 nedy (1967), Raney (1966), U.S. Department of 

 Interior, Federal Water Pollution Control Admin- 

 istration (1967), and Wurtz and Renn (1965). 



The temperatures of the surface waters of the 

 United States vary from 32 to over 100 F as a 

 function of latitude, altitude, season, time of day, 

 duration of flow, depth, and many other variables. 

 The agents that may affect the natural temperature 

 are so numerous that it seems unlikely that two 

 bodies of water, even in the same latitude, would 

 have exacrty the same thermal characteristics. The 

 fish and other aquatic life occurring naturally in 

 each body of water are species or varieties that are 

 competing there with various degrees of success 

 depending on the temperature and various other 

 conditions existing in that habitat. This adaptation 

 extends not only to temperature and the range over 

 which it can vary, but also to such factors as day 

 length and the other species of animals and plants 

 in the same habitat. The interrelationships of spe- 

 cies, day length, and water temperature are so inti- 

 mate that even a small change in temperature may 

 have far-reaching effects. An insect nymph in an 

 artificially warmed stream, for example, might 

 emerge for its mating flight too early in the spring 

 and be immobilized by the air temperature. Simi- 

 larly, a fish might hatch too early in the spring to 

 find an adequate amount of its natural food orga- 

 nisms because the food chain depends ultimately 

 on plants whose abundance in turn, is a function of 

 day length and temperature. The inhabitants of a 

 water body that seldom becomes warmer than 70 F 

 are placed under stress, if not killed outright, by 

 90 F water. Even at 75 to 80 F, they may be un- 

 able to compete successfully with organisms for 

 which 75 to 80 F is a favorable temperature. Simi- 

 larly, the inhabitants of warmer waters are at a 

 competitive disadvantage in cool water. 



Although in a rigorous climate, an animal can 

 endure the extremes of temperature at appropriate 

 seasons; it must be cooled gradually in the fall if it 

 is to become acclimatized to the cold water of 

 winter and warmed gradually in the spring if it is to 

 withstand summer heat. Further, an organism 

 might be able to endure a high temperature of 92 

 or 95 F for a few hours, but it could not do so for 

 a period of days. Having the water change gradu- 

 ally with the season is important for other reasons: 



an increasing or decreasing temperature often 

 serves as the trigger for spawning activities, meta- 

 morphosis, and migration. Some fresh water orga- 

 nisms require that their eggs be chilled before they 

 will hatch properly. 



In arriving at suitable temperature criteria, the 

 problem is to estimate how far the natural tem- 

 perature may be exceeded without adverse effects. 

 Whatever requirements are suggested, a seasonal 

 cycle must be retained, the changes in temperature 

 must be gradual and the temperature reached must 

 not be so high or so low as to damage or alter the 

 composition of the desired population. In view of 

 the many variables, it seems obvious that no single 

 temperature requirement can be applied to the 

 United States as a whole, or even to one State; the 

 requirements must be closely related to each body 

 of water and its population. To do this a tempera- 

 ture increment based on the natural water tempera- 

 ture is more appropriate than an unvarying num- 

 ber. Using an increment requires, however, that 

 we have information on the natural temperature 

 conditions of the water in question, and the size of 

 the increment that can be tolerated by the desired 

 species. 



If any appreciable heat load is introduced into a 

 stream, it must be recognized that the species' 

 equilibrium will likely be shifted towards that char- 

 acteristic of a more southerly water. 



The seasonal temperature fluctuation normal to 

 the desired biota of a particular water must be 

 maintained. Further, the sum of any increase in 

 temperature plus the natural peak temperature 

 should be of short duration and below the maxi- 

 mum temperature that is detrimental for such 

 periods. 



Recommendation for Warm Waters: To maintain a 

 well-rounded population of warm-water fishes, the fol- 

 lowing restrictions on temperature extremes and tem- 

 perature increases are recommended: 



( 1 ) During any month of the year, heat should not 

 be added to a stream in excess of the amount that will 

 raise the temperature of the water (at the expected 

 minimum daily flow for that month) more than 5 F. 

 In lakes and reservoirs, the temperatures of the epi- 

 limnion, in those areas where important organisms are 

 most likely to be adversely affected, should not be 

 raised more than 3 F above that which existed before 

 the addition of heat of artificial origin. The increase 

 should be based on the monthly average of the maxi- 

 mum daily temperature. Unless a special study shows 

 that a discharge of a heated eflluent into the hypolim- 

 nion or pumping water from the hypolimnion (for dis- 

 charging back into the same water body) will be desir- 

 able, such practice is not recommended. 



(2) The normal daily and seasonal temperature 

 variations that were present before the addition of heat, 

 due to other than natural causes, should be maintained. 



(3) The recommended maximum temperatures that 

 are not to be exceeded for various species of warm- 

 water fish are given in table III-l. 



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