242 P. L. Gersper et al 



600 



o 

 ■o 



E 

 o 



o 



c 



3 



FIGURE 7-11. Daily runoff and its concentration of 

 NOi-N, NH4-N, and organic nitrogen during June 1973. 

 (Data from Miller and Alexander, unpubl. and Barsdate 

 and Alexander 1975.) 



The relatively low concentrations of nitrate at the start of snowmelt 

 suggest that the high ammonium levels observed at this time are pro- 

 duced by leaching of animal excreta and plant material, rather than being 

 the result of the concentration in the early meltwater of the ions already 

 present in the snowpack. Leaching of biological material is also sug- 

 gested by the high levels of organic nitrogen, since little or no organic 

 matter is contributed by snowfall. During the summer, only an estimated 

 3 mm of the 64 mm of precipitation is lost in runoff. The loss to summer 

 runoff is 7.5 mg N m"^ — approximately 20% of the loss during snow- 

 melt, or one-third of the input from precipitation during the summer. 



The dynamics of phosphorus loss by runoff are somewhat different 

 from those described above for nitrogen (Table 7-5). A phosphorus loss 



