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Ref. No. [UMCES] CBL 2015-013
ACT VS15-06
were omitted from statistical summaries. The original range in ambient pH measured by the
SAMI-pH (PR) was 6.606 to 9.305 compared to 8.013 to 8.526 for the reference pH
measurements. If we exclude the 51 observations that are suspect, the range was reduced to
7.658 – 8.687, which agrees much closer to that of the reference data. The bottom panel presents
the complete time series of the difference between the SAMI-pH (PR) and reference sample for
each matched pair (n=98 observations). If we exclude seven outliers in the matched dataset
during the malfunction the average difference of the SAMI-pH (PR) and reference was 0.021
±0.047 (N=92), with a total range of -0.095 to 0.177. A cross-plot of the matched observations is
given in figure 19. If we exclude the suspect data, the linear regression was highly significant
with a slope of 0.91, an intercept of 0.76 and r
2
= 0.80.
The SAMI-pH (mCP) unit operated continuously during the entire deployment and
generated 2665 observations based on its 15 minute sampling interval. No internal calibration
cycles were included in the program on this unit. Time series results of the SAMI-pH (mCP) and
corresponding reference pH results are given in figure 20. The range in ambient pH measured by
the SAMI-pH (mCP) was 7.813 to 8.405 compared to 8.013 to 8.526 for the reference pH
measurements The bottom panel presents the time series of the difference between the two
results for each matched pair (n=98 observations). The average and standard deviation of the
difference for the entire deployment was -0.162 ±0.045 with a total range of -0.333 to -0.068. A
cross-plot of the matched observations is given in figure 21. The linear regression was highly
significant (<0.001, r
2
= 0.81) with a slope of 0.816 and an intercept of 1.352.
A summary plot of the SAMI-pH versus dye reference pH for all sites is shown in figure
22. The SAMI-pH responded consistently among all test sites which covered a salinity range of
freshwater to full seawater and temperatures from 3-26
o
C. As expected based on its
characterized operational properties, there was a consistent offset in results reported within the
Great Lakes test for the SAMI-pH with MetaCresol Purple indicator dye compared with the unit
operating with the Phenol Red dye indicator. After removing the 51 outliers, the average
difference between the two SAMI-pH units used for the freshwater test was 0.177 ±0.079, with a
total range of -0.375 to 0.393.
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