August 1958 



GRAVEL BAR I 



G 



August 1958 



^ 



k. 



k- 9 . ' P 



Figure 10. --Dissolved oxygen levels at study area F (14-foot tide 

 level of Twelvemile Creek). Samples were obtained 7 to 10 inches 

 beneath gravel surface at points shown. 



Figure 11. --Dissolved oxygen levels at study area G (17-foot tide 

 level of Twelvemile Creek). Samples were obtained 7 to 10 inches 

 beneath gravel surface at points shown. 



TABLE 5. — Estimates of the mean dissolved oxygen levels of intragravel water in Twelvemile Creek 



September 1958 



November 1958 



Sampling area 



Sample 

 size 



95 -percent 

 confidence interval 

 estimates of mean 



Sample 

 size 



95 -percent 

 confidence interval 

 estimates of mean 



Intertidal 

 Upstream 



93 6.3 mg./l.<|j.< 7.4 mg./l. 

 100 -i.S mg./l. <|.i< 6.1 mg./l. 



50 8.3 mg./l.<fx< 9.5 mg./l. 

 50 8.0 mg./l. <|x< 9.6 mg./l. 



SUMMARY 



1. Evidence is presented that mortality of 

 pink and chum salmon embryos is high. One 

 factor thought to contribute to high mortality 

 is low streamflow which may be accompanied 

 by a -eduction of dissolved oxygen content 

 of intragravel water. 



2. Equipment and techniques employed to 

 sample dissolved oxygen content of intra- 

 gravel water are described. An important 

 component of this equipment is a lightweight, 

 inexpensive plastic standpipe. 



3. Two precautions necessary to insure the 

 procurement of reliable water samples are 

 discussed. They are (1) standpipes which 

 should be left in the streambed for 24 hours 

 or longer before sampling and (2) only small 

 water samples (about 30 ml.) which should be 

 removed. 



4. Temporal changes in dissolved oxygen 

 content of intragravel water are reported. 

 Observed temporal changes are discussed 

 under three categories--daily, seasonal, and 

 yearly. It was found that dissolved oxygen 

 content of intragravel water fluctuated daily 



12 



