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Ref. No. [UMCES] CBL 2016-010
ACT VS16-01
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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. 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 from sample handling. Approximately
10 - 12 independent sampling events were conducted each week. At least once per week an intensive
sampling event was conducted to capture the maximum diurnal range of dissolved oxygen
concentrations. Once per week field duplicates were collected to examine fine-scale variability around
the mooring site. Approximately 120 comparative reference samples were collected over the 3 - 4
month-long deployments.
In conjunction with each water sample collection, each deployment site also recorded site-
specific conditions. The following information, logged on standardized datasheets were transmitted
electronically on a weekly basis to the ACT Chief Scientist, for data archiving and site performance
review:
•
Date, time (local) of water sample collection.
•
Barometric pressure from nearest weather station at time of water sample collection.
•
Weather conditions (e.g., haze, % cloud cover, rain, wind speed/direction) and air temperature at
time of water sample collection.