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Ref. No. [UMCES] CBL 2017-050
ACT VS17-05
4
regression of the measurement differences versus DOC concentration was significant (p=0.008;
r
2
=0.43), with a slope of 0.013 and intercept of 0.118.
A 32 day field deployment occurred from May 26 through June 27 in the Maumee River, at
the facilities of the Bowling Green, Ohio Water Treatment Plant. The Real-NO3 operated
successfully during 31 of the total 32 day deployment, sampling at 5 minute intervals. The
instrument shut down on 5/31 and was rebooted on 6/1 per manufacturer’s instructions resulting in
the loss of one day of data. The Real-NO3 generated 8827 accepted observations out of a possible
9156 for a data completion result of 96.4%. In total, 11 were omitted as outliers due to extreme
range (<-0.01 or >25 mgN/L) and 318 values were missing from the inoperable period. The
average and standard deviation of the measurement difference between instrument and reference
NO
3
measurements for each matched pair (n=47 of a possible 51 observations) over the total
deployment was 0.312 ± 1.029 mgN/L with a total range of -3.35 to 1.15 mgN/L. There was no
significant trend in measurement difference over time as estimated by linear regression (p= 0.28;
r
2
=0.026). A linear regression of instrument versus reference measurement was highly significant
(p<0.0001; r
2
= 0.75) with a slope of 0.96 and intercept of 0.38.
An 84 day moored field test was conducted in Chesapeake Bay from July 18 to October 10,
2016. The Real-NO3 operated continuously for 69 days until 9/24 when air purge system
malfunctioned. The system was bypassed per manufacturer’s instructions and the instrument
restarted on 9/30. The instrument returned 22,345 observations out of a possible 24,144 based on
approximate 5 minute sampling intervals for a data completion rate of 93%. The average and
standard deviation of the measurement difference between instrument and reference NO
3
measurements for each matched pair (n=100 of a possible 103 observations) over the total
deployment was 0.083 ±0.022 mgN/L, with the total range of differences between 0.018 to 0.166
mgN/L. There no significant trend in measurement difference over time during the deployment
(p=0.681; r
2
=0.002). A linear regression of the data was significant (p=0.0002; r
2
= 0.132), with a
slope of 0.680 and intercept of 0.085. For the calibration set-up at this field test, the Real-NO3
significantly over-predicted concentrations.
A one month long moored field test was conducted in Kaneohe Bay from October 3, 2016
to November 2, 2016. The Real-NO3 was not deployed at HIMB at the manufacturer’s decision.