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Ref. No. [UMCES] CBL 2016-014
ACT VS16-05
4
At Houghton, MI the field test was conducted under the ice over 104 days with a mean
temperature and salinity of 0.7
o
C and 0.01. During the pre-tank test the HL4 started reporting
errors; the manufacturer was notified but could not get another sensor to Houghton in time for
deployment. It was decided to try the malfunctioning instrument, but it returned no data. The
DS5X was also not supplied to this site for testing so no instrument results are available for this
field test.
At Chesapeake Biological Lab, the field test was conducted over 78 days with a mean
temperature and salinity of 25.6
o
C and 10.9. The HL4 was deployed on shore power due to the
length of the deployment. Over the 4
th
of July weekend, the cable was severed underwater,
shorting the instrument. Upon return to the manufacturer, only 5 days of data was recovered from
the instrument, however, it is not certain whether the instrument stopped functioning on 5/25 or
whether data was lost due to the impact of the cord being severed and shorting out the instrument.
The DS5X sonde was also deployed at this field sit but a programming error by ACT personnel
resulted in the instrument not being fully enabled for the deployment. The average and standard
deviation of the measurement difference over the abbreviated deployment range was 0.685 ± 0.322
mg/L with a total range of -0.12 to 1.06 mg/L. The higher than expected offset may indicate the
instrument was malfunctioning even at the onset of the deployment.
At Kaneohe Bay, HI the field test was conducted over 121 days with a mean temperature
and salinity of 25.8
and 33.4
o
C. The HACH HL4 stopped functioning on 10/25/15, 33 days into
the deployment resulting in a 26% data completion rate. The measured DO range from our 129
discrete reference samples was 3.63 – 9.85 mg/L compared to a range of 2.02 to 10.88 mg/L
reported by the HL4. The average and standard deviation of the differences between instrument
and reference readings (n=39 of 129 potential observations) were 0.217± .322 mg/L, with a total
range in the differences of -0.725 to 0.769 mg/L. The drift in instrument response showed no
statistically significant trend over time based on a linear regression of the data (slope = 0.0007
mg/L/d; r
2
= 0.0004; p=0.91). A linear regression of the instrument versus reference data (r
2
=
0.95; p<0.0001)) had a slope of 1.115 and intercept of -0.514. The HACH DS5X reported data
throughout the entire deployment and generated 2827 observations based on its 60 minute
sampling interval over the 17 week deployment. However, only 2434of the measurements were
considered acceptable based on our approach of excluding values that were more than 2 mg/L from
reference sample over a similar timeframe. The accepted data resulted in a data completion rate
for this deployment of 86%. Accepted DO measurements by the DS5X ranged from 1.88 to 10.97
mg/L. The average and standard deviation of the differences between instrument and reference
readings (limited to ± 2.0 mg/L DO; n=53 of 129 potential observations) were 0.62 ± 0.744 mg/L,
with a total range in the differences of -1.923 to 1.970 mg/L.
There was a small, but statistically
significant, drift in instrument offset over time (slope = 0.019 mg/L/d; r
2
= 0.52; p<0.0001). A
linear regression of the instrument versus reference data (r
2
= 0.872; p<0.0001)) had a slope of
1.143 and intercept of -0.727.
Overall, the response of the Hach LDO sensors during field testing were generally
consistent across the concentration range within a given test site, as well as over the wide range of
DO conditions (4 - 14 mg/L) across sites, regardless of temperature or salinity. A linear regression
of the accepted instrument versus reference data (r
2
= 0.91 p<0.0001) for the field tests had a slope
of 1.151 and intercept of -0.725.
The HL4 was evaluated in a profiling field test in the Great Lakes at two separate locations
in order to experience both normoxic and hypoxic hypolimnion. In Muskegon Lake, the