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Ref. No. [UMCES] CBL 2016-016
ACT VS16-07
4
maintained commonly at 15
o
C. The calculated τ
90
was 52 s during high to low transitions and 48 s
for low to high transitions covering the 8 mg/L DO range.
At Houghton, MI a field deployment test was conducted under the ice over 104 days with a
mean temperature and salinity of 0.7
o
C and 0.01. The Troll 9000 RDO operated successfully
throughout the entire 15week deployment and generated 9859 observations based on its 15 minute
sampling interval for a data completion result of 100%. The ambient DO range captured by the
reference samples was 10.249 to 14.007 mg/L compared to the slightly broader dynamic range of
9.33 to 14.71 mg/L recorded by the Troll 9000. The average and standard deviation of the
measurement difference over the total deployment was 0.680 ± 0.072 mg/L with a total range of
0.422 to 0.940 mg/L. The drift rate of instrument offset, estimated by linear regression (r
2
=0.29;
p<0.001), was -0.001 mg/L/d. This rate would include any biofouling effects as well as any
electronic or calibration drift. A linear regression of the instrument versus reference measurements
over the first month (r
2
= 0.98; p<0.0001) produced a slope of 0.93 and intercept of 1.61, indicating
an initial calibration offset.
At Chesapeake Biological Lab, a field deployment test was conducted over 78 days with a
mean temperature and salinity of 25.6
o
C and 10.9. The Troll 9000 generated 1879 acceptable
measurements (based on ± 2 mg/L from nearest reference sample) from a possible 3639
observations based on its 30 minute sampling interval for a data completion result of 52%. The
ambient DO reported by reference samples was 4.370 to 10.858 mg/L compared to the broader
dynamic range of 2.01 to 12.18 mg/L measured by the Troll 9000. The average and standard
deviation of the difference between instrument and reference measurements for the deployment
was 0.550 ±0.409 mg/L, with the total range of differences between -0.420 to 1.068 mg/L. The
drift rate of instrument offset for the subset of data was -0.146 mg/L/d (r
2
=0.814). This rate would
include any biofouling effects as well as any electronic or calibration drift. However it is likely
that data included after 6/20 reflect a failing instrument and not a normal drift response. A linear
regression of the instrument versus reference measurements for the first month of the deployment
(r
2
= 0.699, p<0.001) produced a slope of 1.234 and intercept of -1.384.
At Kaneohe Bay, HI a field deployment test was conducted over 121 days with a mean
temperature and salinity of 25.8
and 33.4
o
C. The Troll quit operating on after 26 days and
generated 579 out of 2826 possible observations based on its hourly sampling interval for a data
completion result of 21%. The average and standard deviation of the differences between accepted
instrument measurements and reference readings (n=33 of possible n=129) were -0.032 ±
0.402mg/L, with a total range in the differences of -1.458 to 0.482 mg/L. No calculation of a drift
rate is included given the short operating interval and high variability which suggested an
immediate problem within the instrument. A linear regression of instrument versus reference
measurements for the subset data (r
2
= 0.96, p<0.001) had a slope of 1.117 and intercept of -0.692.
Overall, the Troll 9000 showed good linearity across all three salinity ranges including
fresh, brackish, and oceanic water, covering a dissolved oxygen range if between 4 to 14 mg/L. A
global linear regression of the composited data (r
2
= 0.963; p<0.001)) had a slope of 1.086 and
intercept of -0.351.
The Troll 9000 was evaluated in a profiling field test in the Great Lakes at two separate
locations in order to experience transitions from surface waters into both normoxic and hypoxic
hypolimnion. In Muskegon Lake, the temperature ranged from 21.0
o
C at the surface to 13.5
o
C in
the hypolimnion, with corresponding DO concentrations of 7.8 and 2.8 mg/L, respectively. In