fish) by increasing their metabolic rates and by reducing the solubility of 

 oxygen. The accelerated biological activity demands increased oxygen, which 

 may result in low levels of dissolved oxygen. In general, water temperature 

 controls spawning and hatching of fish and aquatic invertebrates, regulates 

 their activity, and stimulates or suppresses growth and development (Jaine et 

 al. 1977). In addition, rapid changes in temperature can kill organisms. 

 Winter shutdown of a power plant is particularly likely to result in severe 

 thermal stress and possible mortality in organisms that have become acclimated 

 to warm conditions created by thermal discharge. 



High volumes of thermal waste discharged into small bodies of water with 

 relatively little current may become the primary mixing force and increase 

 flushing rates, which could induce higher sedimentation. The effects of 

 increased sedimentation in estuarine systems are discussed under "Dredging" 

 above . 



Small changes in water temperature changes (<5°C) probably have little or no 

 effect on phytoplankton populations, since temperature change is relatively 

 small after the heated water is mixed with riverine, estuarine, and marine 

 water. Mortality to phytoplankton due to entrainment was insignificant at 

 Maine Yankee Atomic Power Plant in Montsweag Bay (McAlice et al. 1978). 



In recent years, Vadas and coworkers (1976) have produced a long-term data 

 base on growth and reproduction of Maine macroalgal populations before and 

 during exposure to heated discharges and in unexposed control areas. They 

 examined the effects of thermal discharges from Maine Yankee Atomic Power 

 Plant in Wiscasset (region 2). Compression of the intertidal macroalgae into 

 narrower and less dense bands was found in areas of heated discharge; this did 

 not take place in control areas (Vadas et al. 1976). The dominant intertidal 

 algae ( Ascophyllum nodosum and Fucus vesiculosus ) showed some rearrangements 

 and the growth of A. nodosum sometimes was stimulated in areas receiving 

 heated effluent. While floral composition may be altered extensively on some 

 coasts (North 1969; and Wood and Zieman 1969), no loss of macroalgal species 

 due to thermal loading was found in Maine. 



The effects of thermal loading on eelgrass are poorly understood. Within 

 areas with restricted temperature limits, higher temperatures could stimulate 

 growth (Thayer et al. 1975). At higher temperatures, however, plants may 

 undergo heat stress. Available data suggest that in areas farther south than 

 Maine (Dillon 1971) eelgrass has a higher temperature tolerance (30°C; 86°F) , 

 while populations on Mt. Desert Island (region 5) may undergo heat stress at 

 temperatures above 20°C (68°F; Setchell 1929). 



The effects of power plants on zooplankton, including fish and shellfish 

 larvae, have been studied intensively. Planktonic organisms carried into 

 cooling systems by water intake mechanisms pass through the intake screens and 

 the condensers and are discharged into the plume. These organisms are not 

 only subjected to short-term elevated temperatures, but they may be killed by 

 mechanical devices, pressure changes, and exposure to chemicals as they pass 

 through the power plant. Studies have shown that zooplankton mortality from 

 passing through the cooling system varies considerably, from as low as 8% to 

 as high as 95% (e.g., Heinle 1969; Barnett and Hardy 1969; Brooks 1970; Johns 

 Hopkins University 1970; Hair 1971; Kelly 1971; Ryther et al. 1973; Carpenter 

 et al. 1974; Normandeau Associates 1974; and Nelson et al. 1976). Under some 



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