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Ref. No. [UMCES] CBL 2016-015

ACT VS16-06


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


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


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


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


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.