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Ref. No. [UMCES] CBL 2016-011

ACT VS16-02


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 5s continuously for eight minutes following the

exchange. 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


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.

Moored Field Tests

Field Deployment Sites and Conditions

A four month moored deployment was conducted at Michigan Technological University’s

Great Lakes Research Center dock in Houghton, MI. Instruments were deployed in January and

kept under ice cover until April. Instruments were programmed to sample at a minimum frequency

of once per hour. ACT collected reference samples twice per day for 4 days per week during the

entire deployment. Instruments were moored at approximately 4m depth and surface access

through the ice was maintained by gentle circulation with a propeller to allow deployment of the

Van Dorn sampling bottle. The goal of this test application was to demonstrate instrument

performance (reliability, accuracy, and stability) in winter-time environmental conditions and to

demonstrate the ability to operate continuous observations under ice.

A three month moored deployment was conducted at the Chesapeake Biological Lab Pier,

Solomons, MD. Instruments were deployed between May and August during a period of warming

temperatures and high biological production. Instruments were moored at fixed depth of 1m on a

floating dock. Instruments were programmed to sample at a minimum frequency of once per hour.

ACT collected reference samples twice per day for 3 days per week and collected six samples on

one day per week during the entire deployment. The intensive sampling was spaced to capture the