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Ref. No. [UMCES] CBL 2016-015
ACT VS16-06
8
at the depth of the sensor heads (ca. -0.5m). All reference samples were collected while the gas
sparging was off and took approximately 1 minute to complete. Reference samples were processed
and analyzed as defined below.
The order of the test conditions were 15 then 5 then 30
o
C, going
from 0 then 10 then 34 salinity at each temperature.
Precision Test at various DO concentrations
Instrument precision was evaluated under stable conditions generally achieved at the start
of each trial’s day. Instruments were equilibrated to each test condition for a minimum of one hour
prior to testing. The sampling frequency for test instruments was 1 minute with reference samples
matching instrument sampling to monitor for drift in tank DO. At least 6 reference samples were
collected over a 30 minute instrument precision evaluation trial. Reference samples were processed
and analyzed as defined below.
Functional Response Time Test
A functional response time test was conducted by examining measurements during a rapid
exchange across a large gradient in dissolved oxygen for a fixed temperature (15
o
C) in deionized
water, following the approach described in Bittig et al. 2014. The reservoirs of the thermostat baths
were constantly bubbled with either N
2
gas or air to maintain discrete DO levels. A submersible
pump was added to each bath to ensure uniform flow and oxygen conditions and instruments were
mounted at a fixed position within the baths to minimize variance due to instrument manipulation.
Instruments were programmed to measure every 10s continuously for eight minutes following the
exchange. (Note: instruments were mistakenly not programmed to measure at their highest
frequency and sampling rate will affect the calculated response time). For instruments with the
capability, real-time monitoring of instrument output was monitored to verify a steady state reading
had been obtained. Instruments were moved from the high DO concentration to the low DO
concentration and subsequently reversed to check for response hysteresis. During transitions, care
was taken to minimize carryover by shaking off residual water. The sensor was then carefully
inserting into the new bucket and mixed by hand to ensure no bubble entrapment and full exposure
to the new solution. Reference samples from each reservoir were taken at the beginning and end of
the exposure. The test instrument was equilibrated in the high DO reservoir for at least 30 min
prior to the exchange to ensure temperature equilibration.
Lab-based Stability Test
A laboratory stability test was conducted to examine potential instrument drift in a non-
biofouling environment. These results are contrasted to the stability of measurement accuracy
observed in the long-term field mooring deployments. The test occurred over 56 days, with daily
temperature fluctuations of approximately 10
o
C, achieved by alternating the set point of the
recirculation chiller. Reference samples were collected at minimum and maximum temperatures at
least 3 times per week. The test was conducted in deionized water at saturated air conditions.
Tanks were well circulated and open to the atmosphere. Water in the test tank was exchanged as
needed if there was any indication of biological growth. Instruments stayed continuously
submerged and were not exposed to air during any water exchange. The goal of
comparisons of
accuracy over time between the field and a sensor deployed similarly in the laboratory is intended
to provide insight into drift and reliability intrinsic to the instrument relative to changes that may
result from biofouling.