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Ref. No. [UMCES] CBL 2015-008
ACT VS15-01
18
Table 1.
Results of burst sample analysis for the Lab Test to demonstrate consistency of test tank
conditions and repeatability of dye pH measurements.
Date
Measurement
Temperature
(
o
C)
Salinity
Time Interval
(min)
(# Obs)
Mean
Std Dev
CV
12/11/12
20.4
35
24 (n=5)
7.783
0.0021
0.026
12/15/12
20.7
35
10 (n=3)
7.762
0.0035
0.045
12/18/12
11.0
35
16 (n=4)
7.867
0.0017
0.022
1/4/13
29.8
22
8 (n=2)
7.973
0.0018
0.023
1/8/13
12.0
22
30 (n=5)
8.141
0.0055
0.068
1/15/13
20.5
22
29 (n=5)
7.860
0.0005
0.001
1/31/13
12.5
0.3
35 (n=5)
8.277
0.0054
0.065
2/6/13
20.4
0.3
65 (n=5)
7.881
0.0024
0.030
2/8/13
30.4
0.3
60 (n=5)
7.644
0.0013
0.018
2/12/13
25.5
34
39 (n=5)
7.934
0.0010
0.013
Overall Average
0.0025
0.032
The complete ten week time series for the CSI pH sensor and corresponding reference pH
results are shown in Fig. 3. Although temperature and salinity were tightly controlled and the
test tank received a single batch of continuously circulated source water, the pH varied
considerably during each of the trials due to biological activity. These time series results also
include the rapid pH shifts that were conducted once a week under each of the test T/S
conditions using acid/base additions. Detailed plots of each pH transitions are provided in
Appendix I. In general, pH was varied by around 1.2 pH units during the acid/base additions and
conditions maintained at each new value for approximately an hour.
The CSI sensor operated continuously throughout the entire lab test and generated 6294
pH measurements at 15 minute intervals. The total range of pH measured by the CSI was 6.805
to 8.560, compared to the range of our reference pH of 6.943 to 8.502. The CSI measurements
tracked changing pH conditions among all water sources and temperature ranges including the
rapid pH shifts from acid/base additions, but the magnitude and direction of the offset changed
for each water type (Fig.3). The mean of the differences between the CSI pH measurement and
reference pH was -0.019 ±0.319 (N=265), with a total range of -0.668 to 0.624. Instrument
measurements conducted after ten weeks with the second seawater trial showed an increase
offset (mean difference = 0.345 ±0.020; N=9) compared to measurements from the first week
(mean difference = 0.084 ± 0.055; N=27) (data not shown).