inorganic nitrogen in Silver Bow Creek were an order of 

 magnitude higher than any other stream monitoring station in 

 the Clark Fork Basin. The EPA nitrogen (1,000 ug/1) and 

 phosphorous (50 ug/1) criteria were routinely exceeded by a 

 large margin — up to 32 times for phosphorus and up to four 

 times for nitrogen — at most monitoring locations on the 

 creek. 



The highest nutrient concentrations in Silver Bow Creek 

 occurred at monitoring station 1, Silver Bow Creek below the 

 Colorado Tailings. The station is located a short distance 

 downstream of the Butte municipal wastewater discharge, which 

 is the principal source of nutrients in the creek. During 

 periods of low streamflow, more than half the Silver Bow 

 Creek flow consists of sewage effluent. From monitoring 

 station 1 downstream to the Warm Springs Ponds, nutrient 

 concentrations (Figure 3-27) and loads declined somewhat, 

 presumably as a result of dilution from cleaner tributaries 

 or ground water inflows, or both, and probably to a lesser 

 extent from biological uptake. However, concentrations 

 remained sufficiently high to categorize the stream as 

 grossly polluted. Silver Bow Creek does not harbor extensive 

 developments of algae despite its excessive nutrient 

 concentrations. Algal bioassays conducted several years ago 

 for DHES (Greene et al. 1986) indicated that the potential 

 for algal growth in Silver Bow Creek was limited by toxic 

 metals, most likely copper. Copper is phytotoxic at 

 relatively low concentrations and is widely used as an 

 algicide, e.g., copper sulfate. 



Warm Springs Ponds 



The Warm Springs Ponds were very effective at decreasing 

 Silver Bow Creek phosphorus concentrations (Figure 3-27, 

 monitoring station 3 versus 4) and loads during FY 86-87. 

 Reductions in both nitrogen and phosphorus concentrations and 

 loads were comparable and averaged about 3 . 5-fold less in the 

 pond outlet as compared with Silver Bow Creek above the 

 ponds. Biological assimilation, denitrification, and 

 settling of suspended solids with adsorbed nutrients were 

 presumably the responsible factors. 



The ponds effectively reduced nitrogen concentrations to 

 levels below the EPA criterion, on the average. Only 

 infrequent, small-scale exceedences of the nitrogen criterion 

 in the pond discharge were documented in FY 86, and no 

 exceedences were measured in FY 87. Although phosphorus 

 concentrations were significantly reduced, they rarely fell 

 below the problem level. Measurements of total phosphorus in 

 the pond discharge exceeded the EPA criterion in 80 to 90 



3-87 



