7 / 73
Ref. No. [UMCES] CBL 2016-010
ACT VS16-01
7
Tests were run such that all 4-6 DO concentrations were tested for a fixed temperature and salinity
on the same day.
The tests began at ambient, near air saturation, conditions following overnight
equilibration of tank water to the test salinity and temperature. Subsequently DO were dropped to near
0 mg/L and increased stepwise to the highest concentration
. Instruments were allowed to equilibrate at
the fixed temperature and salinity for 1 h before the start of that day’s trial. Sparging with each DO gas
concentration was conducted for a minimum of 60 minutes prior to the start of data collection and
reference sampling. For each test condition, the test instruments were programmed to sample at no
slower than 1 minute intervals and reference samples were collected at 6 timepoints spaced 5 minutes
apart for each of the fixed conditions. For three of the timepoints duplicate samples were collected
from two different sampling ports mounted at opposite ends of the tank to access heterogeneity within
the tank. Inlets of sampling ports were positioned at the depth of the sensor heads (ca. -0.5m). All
reference samples were collected while the gas sparging was off and took approximately 1 minute to
complete. Reference samples were processed and analyzed as defined below.
The order of the test
conditions were 15 then 5 then 30
o
C, going from 0 then 10 then 34 salinity at each temperature.
Precision Test at various DO concentrations
Instrument precision was evaluated under stable conditions generally achieved at the start of each
trial’s day. Instruments were equilibrated to each test condition for a minimum of one hour prior to
testing. The sampling frequency for test instruments was 1 minute with reference samples matching
instrument sampling to monitor for drift in tank DO. At least 6 reference samples were collected over a
30 minute instrument precision evaluation trial. Reference samples were processed and analyzed as
defined below.
Functional Response Time Test
A response time test was conducted by examining measurements during a rapid exchange across a
large gradient in dissolved oxygen for a fixed temperature (15
o
C) in deionized water, following the
approach described in Bittig et al. 2014. The reservoirs of the thermostat baths were constantly
bubbled with either N
2
gas or air to maintain discrete DO levels. A submersible pump was added to
each bath to ensure uniform flow and oxygen conditions and instruments were mounted at a fixed
position within the baths to minimize variance due to instrument manipulation. Instruments were
programmed to measure every 10s continuously for minutes following the exchange (Note:
instruments were mistakenly not programmed to measure at their highest frequency and sampling rate
will affect the calculated response time). For instruments with the capability, real-time monitoring of
instrument output was monitored to verify a steady state reading had been obtained. Instruments were
moved from the high DO concentration to the low DO concentration and subsequently reversed to
check for response hysteresis. During transitions, care was taken to minimize carryover by shaking off
residual water. The sensor was then carefully inserted into the new bucket and mixed by hand to
ensure no bubble entrapment and full exposure to the new solution. Reference samples from each
reservoir were taken at the beginning and end of the exposure. The test instrument was equilibrated in
the high DO reservoir for at least 30 min prior to the exchange to ensure temperature equilibration.