TABLE 1. — Temporal changes in dissolved oxygen levels''- 

 after placing standpipes 



■'■ Temperature at each point increased about 4° F. during the period 

 of sampling. 



With regard to the second precaution, a 

 test was run to find the effect of removing 

 relatively large volumes of water from stand- 

 pipes. Two 125-nnl. water samples were ob- 

 tained in rapid sequence from each of 41 

 points. The average absolute difference be- 

 tween the sequential samples wasl0.5lmg./l. 

 (range 0.0 mg./l. to 13.21 mg./l.). Figure 

 4 shows the relationship between first and 

 second readings. Those points having no change 

 in dissolved oxygen content fell on the line 

 y = X. At points where the oxygen values were 

 high, the second sample generally gave higher 

 readings than the first, and most of these 

 points were above the line y = x. Lower 



4 6 8 



First sample 

 mg./l. of dissolved oxygen 



Figure 4.--Relationship between dissolved oxygen content of two 

 125-ml. water samples withdrawn less than 1 minute apart. 



readings were generally obtained for second 

 samples at points having low oxygen values, 

 with most readings falling below y = x. Results 

 of this nature might be expected if intragravel 

 water originated from highly oxygenated 

 stream water at points high in dissolved 

 oxygen content and frora poorly oxygenated 

 ground water at points low in dissolved oxygen 

 content. 



Obtaining Data on Spatial Differences 

 and Temporal Changes 



Two sampling procedures were used to 

 obtain data on spatial differences and tem- 

 poral changes in dissolved oxygen level of 

 intragravel water. The first procedure in- 

 volved systematic sampling of relatively small 

 spawning areas, referred to as study areas. 

 Study areas were located in Harris River and 

 Twelvemile, Indian, and Old Tom Creeks 

 (fig. 1). The second procedure involved random 

 sampling within extensive spawning areas 

 which were called sampling areas. The sam- 

 pling areas described in this report were 

 located in Twelvemile Creek. 



Systematic Sampling 



One purpose of systematic sampling was 

 to obtain detailed information on spatial dis- 

 tribution of intragravel dissolved oxygen levels 

 within a spawning bed. To accomplish this, 

 standpipes were distributed uniformly at 5- 

 to 10-foot intervals over each study area. 

 No attempt was made to stratify pipes with 

 respect to surface water depth or velocity. 

 In several study areas, standpipes were driven 

 into bars that received seepage water from 

 the stream. Efforts were made to confine 

 sampling to periods of low to moderately 

 low stream discharge. During each sannpling 

 period an oxygen reading was obtained from 

 every point sampled on two or more con- 



