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Ref. No. [UMCES] CBL 2015-010
ACT VS15-03
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 Idronaut measurement and reference pH was -0.144 ±0.174 (N=181), with a total range of -
0.502 to 0.078.
At Moss Landing Harbor the field deployment test was conducted over 28 days with a
mean temperature and salinity of 16.6
o
C and 33. The measured ambient pH range from our
discrete reference samples was 7.933 – 8.077 (N=84). No results were obtained for the Idronaut
305 Plus for this field deployment test due to a programming error by ACT personnel. It was not
possible to repeat the test since only one instrument was available and it needed to be submitted
to the next test site.
At Kaneohe Bay the field deployment test was conducted over 88 days with a mean
temperature and salinity of 24.5
o
C and 34.4. The measured ambient pH range from our discrete
reference samples was 7.814 – 8.084 (N=101). The Idronaut 305 Plus operated continuously for
the first twenty seven days (total deployment was 88 days) after which there appeared to be a
short in the battery which terminated logging. During its operational period the instrument
generated 2756 observations at 30 minute intervals with a measured range in ambient pH from
7.599 to 8.409. The average and standard deviation of the measurement differences between the
Idronaut and reference pH was 0.107 ±0.093 (N=62), with a total range of -0.030 to 0.387.
At Chesapeake Bay the field deployment test was conducted over 30 days with a mean
temperature and salinity of 5.9
o
C and 12.8. The measured pH range from our discrete reference
samples was 8.024 – 8.403 (N=107). The Idronaut 305 Plus only operated during the first four
days of the deployment and generated 372 pH measurements at 15 minute intervals with a
measured range in ambient pH of 7.798 to 8.135. The average and standard deviation of the
measurement difference between the Idronaut and reference pH was -0.366 ±0.042 (N=18), with
a total range of -0.425 to -0.247.
At Lake Michigan the field deployment test was conducted over 29 days with a mean
temperature and salinity of 21.2
o
C and 0.03. The measured ambient pH range from our discrete
reference samples was 8.013 to 8.526 (N=98). The Idronaut 305 Plus operated continuously
over the 29 days of the deployment and generated 2671 observations at 15 minute intervals with
a measured range in ambient pH of 7.523 to 8.462. The average and standard deviation of the
measurement difference between the Idronaut and reference pH was -0.184 ± 0.081 (N=98) with
a total range of -0.465 to -0.019.
A comparison of the Idronaut 305 Plus pH measurements and dye reference pH across all
sites indicated that the instrument tracked changes in ambient pH at all sites but that the response
factor (slope) and overall offset from the dye reference pH measurements was different at each
site.
Lastly although this instrument experienced several power issues during this verification,
it is worth emphasizing that the continuous 15 – 30 minute time-series provided by the test
instrument was able to resolve a significantly greater dynamic range and temporal resolution
than could be obtained from discrete reference samples. Continuous in situ monitoring or
profiling technologies, such as the Idronaut 305 Plus, provide critical research and monitoring
capabilities for helping to understand and manage important environmental processes such as
carbonate chemistry and ocean acidification, as well as numerous other environmental or
industrial applications.
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