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Ref. No. [UMCES] CBL 2015-014
ACT VS15-07
30
RESULTS of MOORED FIELD TESTS
Moored field tests were conducted to examine the performance of the Xylem EXO pH
sensor to consistently track natural changes in pH over extended deployment durations of 4-8
weeks. In addition, the field tests examined the reliability of the instrument, i.e., the ability to
maintain integrity or stability of the instrument and data collections over time. Reliability was
determined by quantifying the percent of expected data that was recovered and useable. The
performance of the EXO was examined in four separate field deployment tests at various ACT
Partner test sites to include a range of biogeochemical conditions. The range and mean for
temperature and salinity for each test site is presented in Table 2. The final reference
temperature data was computed from the mean of two RBR thermistors and the SeaBird SBE
that were mounted at the same sampling depth as the test instrument. The reference temperature
data and salinity were used to compute ambient pH results from the laboratory results using a
CO2-Sys program (Pierrot et.al., 2006).
Immediately before each deployment the test instrument
was exposed to a certified or internal reference sample for 3-4 measurements to confirm good
working status and provide an initial offset against its latest calibration (Table 3).
Table 2
. Range and average for temperature, and salinity at each of the test sites during the sensor field
deployment. Temperature and salinity were measured by two RBR temperature loggers and a SeaBird
SBE 26 (or SBE26plus) mounted on the instrument rack and the duration of the deployment.
SITE
(deployment period/duration)
Temperature
(
0
C )
Salinity
Moss Landing Harbor
Min.
14.9
30.7
26Aug – 22Sept
Max.
18.6
33.7
(n = 28 days)
Mean
16.6
33.0
Kaneohe Bay
Min.
22.3
32.8
15Nov – 10Feb
Max.
26.5
35.2
(n = 88 days)
Mean
24.5
34.4
Chesapeake Bay
Min.
3.4
9.3
12Mar – 10Apr
Max.
10.1
14.0
(n = 30 days)
Mean
5.9
12.8
Lake Michigan
Min.
11.6
0.024
21Jun – 19Jul
Max.
24.9
0.035
(n = 29 days)
Mean
21.2
0.031
Table 3.
Values for the reference pretest for the Xylem EXO at each deployment site. After calibration
and prior to deployment the EXO was pre-checked in either a CRM or NIST buffer prepared from salts
supplied by Kenneth Pratt (NIST) and characterized by spectrophotometric analysis by ACT personnel.
Deployment Site
Reference
Solution
Measurement
Temperature
Reference
Solution pH
EXO pH 1
EXO pH 2
MLML
Seawater CRM
20
°C
7.97
8.29
8.32
HIMB
Seawater CRM
25
°
C
7.86
9.13
8.81
CBL
Seawater CRM
20
°C
8.00
8.10
N/A
GLERL
NIST Buffer
20
°C
9.23
9.11
9.14