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Ref. No. [UMCES] CBL 2016-012
ACT VS16-03
9
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.
•
Recent large weather event or other potential natural or anthropogenic disturbances.
•
Tidal state and distance from bottom of sensor rack at time of water sample collection.
•
Any obvious problems or failures with instruments.
ACT was responsible for accurately characterizing temperature and salinity surrounding the
mooring with the goal of characterizing micro-stratification or heterogeneity surrounding the
mooring. Four RBR Solo temperature loggers and two SeaBird CTDs were deployed at each
mooring site. Sensors were mounted both at the instrument sampling depth and approximately 0.5
m above the sampling depth.
At the end of each mooring deployment a pre- and post-cleaned comparison of sensor response
to a 100 % saturated water bath was conducted. Upon retrieval the sensor was wrapped in a damp
towel and returned to the lab as quickly as possible. Prior to any cleaning, the sensor was
submerged in a 100 % DO water bath (via bubbling with air) and DO recorded for a minimum of
three readings after an initial 30 minute equilibration period. Then the sensor was removed from
the bath and cleaned of any visible biofouling according to recommended manufacturer
procedures. Following cleaning the sensor was submerged in a second 100% DO water bath to
avoid any biofouling debris carryover and DO recorded for a minimum of three readings after an
initial 30 minute equilibration period. Temperature of both water baths was monitored
continuously and maintained at a constant condition within 0.5
o
C. DO concentration was
maintained at a constant saturated level with bubbling and confirmed by Winkler titration at the
beginning and final instrument reading timepoints.