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Ref. No. [UMCES] CBL 2015-010
ACT VS15-03
for a period of 12 weeks. Instruments were removed from the water only after the test period
was complete.
Instrument Setup
– Prior to deployment, all instruments were set up at the field site by a trained
ACT staff member following established protocols that had been developed in collaboration with
the manufacturers at the training session that occurred in December, 2012 (at the beginning of
the ACT laboratory test). Manufacturers that did not conduct an in-person training session sent
written protocols and video demonstration of desired handling procedures. As appropriate, and
where requested by the manufacturer, submitted test instruments were initially calibrated by
ACT staff using a common batch of commercial, non-dyed, NIST traceable buffers at a pH of
7.02 and 10.06. (Each sensor was calibrated with buffer from its own bottle, but they were all
from the same LOT and shipment). All calibrations occurred in a constant temperature bath at
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, Hawaii,
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 NIST buffers prepared by ACT personnel using salts obtained from
Kenneth Pratt (NIST) or lake water CRMs as appropriate for the instrument. Both the buffers
and the CRMs were characterized by spectrophotometric analysis by ACT personnel. 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.
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