Table 10. — Comparison of mean monthly values of limnological data collected in 1954-55 

 (Sylvester, 1958) with data collected in 1967-68 



Type of data and year 



Month 



Mar. 



May 



June 



July 



Aug. 



Sept. 



Nov. 



Dec. 



Mean 

 value 



Water temperature (° C): 



1954-55 



1967-68 



Dissolved oxygen (p. p.m. ): 



1954-55 



1967-68 , 



Dissolved oxygen 

 (# saturation): 



1954-55 , 



1967-68 



P H: 



1954-55 



1967-68 , 



Turbidity (JTU): 



1954-55 , 



1967-68 , 



Calcium (p. p.m. ): 



1954-55 , 



1967-68 , 



Magnesium (p. p.m. ): 



1954-55 , 



1967-68 , 



Sodium (p. p.m. ): 



1954-55 



1967-68 



5.2 



7.8 



12.5 



11.6 



98 



97 



7.5 

 7.5 



12 



5.5 



17 



15 



0. 



4, 



7. 

 6, 



12. 

 13. 



10. 

 10. 



96 



100 



7.5 



7.6 



3 

 7.7 



17 

 17.5 



1.0 

 4.7 



12.0 

 6.8 



14.5 

 15.6 



11.4 

 9.4 



111 

 94 



7.4 

 7.4 



20 

 13 



20 

 14.5 



0.2 

 3.5 



6.0 

 3.3 



16, 

 19, 



11.3 

 9.7 



116 



104 



7.9 

 7.7 



14 

 7.3 



17.5 

 17.3 



18.9 

 20.8 



9.6 

 8.6 



102 

 95 



8.0 

 7.9 



6 

 4.2 



17 

 18. 



1. 

 4, 



1.0 

 3.7 



18.1 

 19.9 



9.3 

 7.7 



97 

 83 



7.9 

 7.9 



13 

 2.4 



18 

 16.2 



0.7 

 5.3 



4.0 

 6.5 



10.6 

 9.3 



10.5 

 10.8 



94 

 88 



7.9 

 7.1 



4 

 13.8 



21 

 16 



0.6 

 4.8 



16.0 

 7.8 



5.4 

 6.7 



11.7 

 11.0 



92 



89 



7.4 

 7.4 



10 

 9.6 



18 

 16 



10.0 

 6.0 



12.8 

 14.1 



10.8 

 9.9 



101 

 94 



7.7 

 7.6 



10 

 8.3 



18 

 16.3 



0.9 

 4.5 



7.3 

 5.6 



in 1967-68 was actually less saturated with 

 oxygen at any given temperature than it was 

 in 1954-55. Figure 15 shows graphically the 

 comparison of percentage saturation between 

 1954-55 and 1967-68. 



The concentration of magnesium was 

 higher in 1967-68 than that reported by 

 Sylvester (1958) for 1954-55 (table 10). The 

 U.S. Geological Survey (1959a, 1959b), how- 

 ever, did not report such a low concen- 

 tration of magnesium during 1954-55 nor 

 were like differences apparent in calcium 

 concentration, which usually parallels that 

 of magnesium. Therefore, differences in con- 

 centration of magnesium between the data 

 of Sylvester (1958) and those collected 

 in the present study are probably not 

 meaningful. 



Comparison of limnological data for 1954-55 

 with those for 1967-68 does not suggest any 

 significant differences in pH, turbidity, or 

 calcium and sodium concentrations. 



In table 11, 1967 and 1968 data are compared 

 with 1960 data of Sylvester and Carlson (1961). 

 It must be remembered that data for 1967 re- 

 flect conditions only from late July through 

 December. Thus, the maximum chlorophyll a 

 value for 1967 does not indicate alower spring 

 bloom than in 1960 or 1968. Concentration of 

 dissolved oxygen was less in 1967-68 than in 

 I960 as can be seen by comparing percentage 

 saturation of oxygen data for the 3 years. Thus, 

 the concentration of dissolved oxygen in the 

 lower Columbia River appears to be decreasing 

 with time since it was lower in 1967-68 than 

 in either 1954-55 or I960. 



12 



