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Ref. No. [UMCES] CBL 2015-014
ACT VS15-07
11
20.0
o
C (except at HI which was done at 25°C). Any deviation from this temperature was noted
and used to adjust the stated pH values of the buffers as defined on the bottles.
After calibration and prior to deployment (again where appropriate for each instrument)
instruments were exposed to additional certified reference solutions. At Moss Landing, CBL and
Hawaii, 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