Ammonia . Ammonia is a form of nitrogen that is 

 frequently associated with wastewater discharges. Ammonia 

 or its degradation products are readily available for algal 

 uptake and can contribute to nutrient enrichment problems . 

 However, the primary concern with ammonia is that it can be 

 extremely toxic to aquatic life under certain conditions of 

 stream pH and temperature (EPA chronic ammonia toxicity 

 criterion varies depending on pH and temperature) . The 

 potential for ammonia toxicity downstream of wastewater dis- 

 charges in the Clark Fork Basin has been closely monitored in 

 the past and will require continued scrutiny. 



The Butte WWTP effluent is a source of ammonia to 

 Silver Bow Creek. During WQB FY 85-87 sampling, the EPA 

 chronic toxicity criterion for salmonid species (trout) was 

 exceeded in one-third to two-thirds of the samples during the 

 monitoring period for several miles below the outfall. 



Ammonia toxicity was not documented at any of the upper 

 or lower Clark Fork stations during the monitoring period. 

 The effluent from the Missoula WWTP is the largest source of 

 ammonia in the middle river. Ammonia toxicity was not 

 documented below the wastewater mixing zone during FY 85-87 

 WQB sampling. However, because of high levels of ammonia in 

 the discharge and documented exceedences of the ammonia 

 criterion within the mixing zone, further evaluation is being 

 done by WWTP staff. The Frenchtown Mill wastewater also 

 contains relatively high levels of ammonia. To date, 

 exceedences of the criteria have not been documented. 

 However, installation of the color-removal facilities has 

 necessitated daily ammonia monitoring because wastewater 

 dilution rates are lower when color-treated wastewater is 

 being discharged. 



Temperature and Dissolved Oxygen . Stream temperature 

 and concentration of dissolved oxygen affect the survival of 

 aquatic life, particularly salmonids. If a fish is exposed 

 to increased temperatures, more energy is required for basic 

 metabolism, and less energy is available for food acquisi- 

 tion, growth, and reproduction. Stream temperature is 

 affected by many factors, including streamflow, air tempera- 

 ture, exposure to sunlight, the ratio of surface area to 

 volume, ground water inflow, and topography (Braico 1973) . 

 Trout generally prefer temperatures between 52 °F and 64° F, 

 while long-term exposure to temperatures above 75° F may be 

 lethal . 



The amount of dissolved oxygen in streams is an 

 important measure of water quality. Sufficient levels of 

 oxygen are necessary to support a healthy and diverse 

 community of organisms, including fish, aquatic insects, 



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