4 / 47
Ref. No. [UMCES] CBL 2015-009
ACT VS15-02
4
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 ambient pH range from our 107
discrete reference samples was 8.024 – 8.403. The Manta2 operated successfully over the entire
deployment and generated 2756 observations based on its 15 minute sampling interval. Ambient
pH measured by the Manta2 ranged from 8.14 to 8.54. The average and standard deviation of
the measurement difference between instrument and reference pH was 0.12 ±0.02, with the total
range of differences from 0.09 to 0.16 (N=107).
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 pH range from our 98 discrete
reference samples was 8.013 - 8.526. The Manta2 operated continuously over the entire
deployment and generated 2680 observations based on its 15 minute sampling interval. Ambient
pH measured by the Manta2 ranged from 7.86 to 8.51. The average and standard deviation of
the difference between instrument and reference pH was -0.07 ± 0.04 with a total range of -0.20
to -0.004 (N=98).
A summary plot of all four field tests indicates that the Manta2 responded consistently
with good agreement to reference pH measurements at three of the four test sites. No
explanation or observed failure was discovered to explain the performance at the Moss Landing
test site. Results for the brackish and saline test sites show an expected offset due to calibration
and scale differences between NBS buffers and the pH
total
scale reported by the
spectrophotometric dye measurement.
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 over these deployment durations. Continuous in situ monitoring
technologies, such as the Eureka Manta 2, 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.