silicate (fig. 2) than station 1 and lower in pH 

 (fig. 3), sodium (fig. 4), calcium (fig. 5), and 

 magnesium (fig. 5). Records of the U.S. 

 Geological Survey (1964) show the same dif- 

 ference between these variables in waters of 

 the Columbia at The Dalles Dam and the 



2 3 4 

 STATION 



Figure 2. — Average concentration of silicate at each 

 sampling station, July 1967 through December 1968. 



2 3 4 5 

 STATION 



Figure 3. — Average pH value at each sampling station, 

 July 1967 through December 1968. 



Willamette River at Salem, Oreg. Because 

 the Willamette enters the Columbia between 

 stations 1 and 2, this tributary is most likely 

 responsible for the higher silicate and lower 

 pH, sodium, calcium, and magnesium at station 

 2. 



2 3 4 5 

 STATION 



Figure 4. — Average concentration of sodium at each 

 sampling station, July 1967 through December 1968. 



I 2 3 4 5 6 7 



STATION 



Figure 5. — Average concentrations of calcium (a) and 

 magnesium (b) at each sampling station, July 1967 

 through December 1968. 



