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Ref. No. [UMCES] CBL 2015-009
ACT VS15-02
10
and CBL, instruments were exposed to batches of Seawater CRMs produced by the CO2-QC
facility at Scripps Institution of Oceanography. (CRMs were batched into a single container
before distributing into individual calibration cups for each sensor. Three cuvettes were filled
immediately upon mixing the batch and again at the end of pouring out the solution to measure
pH and ensure consistency of each aliquot.) For the freshwater test in Lake Michigan
instruments were exposed to the NIST buffers or lake water characterized by spectrophotometric
analysis by ACT personnel as appropriate for the instrument. All pre-deployment instrument
measurements of the reference buffers were in a water bath at a constant temperature (20
o
C,
except at HIMB which were at 25
o
C) and all solutions and instruments were pre-equilibrated at
this temperature.
For the deployment, instruments were programmed to record data based on a time
interval that allowed for a 30 day (or 90 day for HI) deployment. Intervals were selected such
that there was a common 30 (or 60) minute interval achieved by all instruments. This schedule
allowed us to coordinate our reference sampling for all instruments. Internal clocks were set to
local time and synchronized against the time standard provided b
y www.time.gov .In high flow
coastal environments, clock drift could lead to significant bias.
Instrument Deployment
– A photograph of each individual instrument and the entire
instrument rack was taken just prior to deployment and just after recovery to provide a
qualitative estimate of biofouling during the field tests. Instruments were set-up as self-
recording on a deployment rack and arranged so that a single representative field sample could
be collected within 1 meter of any individual sampling inlet. The deployment frames were
arranged so that all of the instruments remain at a fixed depth of 1 m below the water surface
(using a float system or fixed dock in environments not affected by tidal changes or strong wave
action). Two calibrated SeaBird CTD packages and four RBR Solo thermistors were attached to
the mooring at each test site in order to accurately characterize the temperature and salinity
heterogeneity surrounding the mooring. In these dynamic coastal regions it was critical to
understand the spatial and temporal dynamics of the water column in order to interpret pH
measurements appropriately.
Instrument Retrieval –
After the instruments were retrieved and cleaned of all removable
fouling according to written procedures provided by the manufacturer, a final exposure test was
conducted in the CRM buffers as defined above. For instruments that pumped samples through
an inlet, the inlet was connected to the manufacturer’s supplied storage bag to ensure that no air
was introduced prior to exposure in the buffers.
Reference Water Sampling Schedule
– The sampling frequency was structured to
examine changes in pH over daily and weekly time scales. Specifically, an intensive sampling
event was conducted once a week that consisted of 5 sample collections within a day. During
four additional days of each week, there was a minimum of twice per day sampling, scheduled in
a manner to capture as much diurnal variation as possible. The initial intensive sampling event
occurred within the first two days of the deployment after all instruments had been deployed, and
the final intensive sampling event occurred during the last two days of the deployment. The
schedule provided a higher density of comparative data at the beginning when instruments
should have been functioning at optimum performance and again after the challenge of a four or
twelve week deployment. The sampling schedule resulted in at least 60 reference samples paired
with instrument measurements. For the 12 week deployment test at HIMB, the sampling scheme
was modified to spread out a similar number of samples over the extended time period. All