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Ref. No. [UMCES] CBL 2016-011
ACT VS16-02
9
maximum range of expected diurnal variation in dissolved oxygen concentrations. The goal of this
test application was to demonstrate instrument performance (reliability, accuracy, and stability)
under high biofouling conditions and over a range of salinity and temperature conditions in a
coastal estuarine environment.
A four month moored deployment was conducted in a shore patch reef at the Hawaii
Institute of Marine Biology (HIMB), Coconut Island, Kaneohe, HI. Instruments were deployed
between September and January. Instruments were moored at approximately 1m depth on a
bottom mounted PVC rack and were programmed to sample at a minimum frequency of once per
hour. Some manufacturers chose to sample more frequently to demonstrate that capability. 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
maximum range of expected diurnal variation in dissolved oxygen concentrations. The goal of this
test application was to demonstrate instrument performance (reliability, accuracy, and stability)
under high biofouling conditions in warm, full salinity coastal ocean conditions.
Field Testing Procedures
The moored deployments were run sequentially, and instrument packages were returned to
manufacturers for reconditioning and calibration in between each successive field test.
Prior to each deployment, instruments were set-up and calibrated if required, as directed by the
manufacturer and demonstrated at a prior training workshop. Sensors were programmed to record
dissolved oxygen data at a minimum of once per hour at the top of the hour for the duration of the
planned deployment. All instrument internal clocks were set to local time and updated before
programming using www.time.gov as the time standard. A photograph of each individual sensor
and the entire sensor rack was taken just prior to deployment and just after recovery to provide a
qualitative estimate of biofouling during the field tests. In the final step before deployment,
instruments were placed in a well aerated fresh water bath, with a known temperature, for 45
minutes and allowed to record three data points as a baseline reference. Reference samples were
drawn at the corresponding sampling times and analyzed for dissolved oxygen using Winkler
titration method described below.
All instrument packages were deployed on a single box shaped rack that allowed all sensor
heads to be at the same depth, with instruments side by side and all sensor heads deployed at the
closest proximity feasible. The rack was deployed so that all sensor heads remained at a fixed
depth of 1 m below the water surface, except as noted above. A standard and calibrated CTD
package was deployed at each test site and programmed to provide an independent record of
conductivity and temperature at the sensor rack during each instrument sampling event. At least
four additional RBR temperature loggers were placed on the rack to capture any spatial variation in
the temperature across the rack.
A standard 4 L Van Dorn bottle was used at each test site to collect water samples for
Winkler titrations. The bottles were lowered into the center of the sensor rack, at the same depth
and as close as physically and safely possible to the sensor heads. The bottle was triggered to close
at the same time as the instruments were measuring to ensure that the same water mass was
compared for DO content. Three replicate 125 ml BOD bottles were filled from each reference
sample and immediately fixed in the field for subsequent Winkler titration analysis as described
below. The order of each sub-sample was recorded and tracked to examine any variation that arose