4 / 48
Ref. No. [UMCES] CBL 2015-012
ACT VS15-05
to 8.409. The average and standard deviation of the measurement difference between the SeaFET
and reference pH was -0.001 ±0.007 (N=107), with a total range of -0.024 to 0.018
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 98
discrete reference samples was 8.013 to 8.526. The SeaFET operated successfully throughout
the entire deployment and generated 2673 observations with a measured range in ambient pH
from 7.770 to 8.594. The average and standard deviation of the difference between the SeaFET
and reference pH for the deployment was -0.183 ± 0.040 (N=98), with a total range of -0.347 to -
0.090. For this deployment test, the SeaFET results are from the internal pH sensor since the
freshwater media does not allow the external reference electrode to function properly.
A summary plot of the SeaFET versus reference pH for all sites shows that the SeaFET
responded consistently among the brackish and saltwater test sites but with a larger offset for the
freshwater test. The SeaFET was calibrated with commercial NBS buffers by Satlantic prior to
the freshwater test and there was no identified reason for the larger offset. However, it should be
noted that the offset was observed during the initial pre-deployment check so likely was a
function of the initial calibration.
Lastly, 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. There were no obvious
changes in the differences between instrument and reference measurements during the duration
of the mooring test, indicating that biofouling and instrument drift had not significantly affected
measurement performance. Continuous in situ monitoring technologies, such as the Satlantic
SeaFET, 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.