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Ref. No. [UMCES] CBL 2016-013
ACT VS16-04
39
Moored Deployment off Coconut Island in Kaneohe Bay, Hawaii
An 18 week long moored field test was conducted in Kaneohe Bay from September 22,
2015 to January 20, 2016. The deployment site was located at 21.43° N x 157.79° W, on the
fringing reef flat surrounding Coconut Island (HIMB) in a depth of 3 meters (Photo 5). Kaneohe
Bay, located on the eastern side of Oahu, Hawaii, is a complex estuarine system with a large
barrier coral reef, numerous patch reefs, fringing reefs, and several riverine inputs. Tides in
Kaneohe Bay are semi-diurnal with mean tidal amplitude of approximately 68 cm day.
Photo 5.
Aerial view of HIMB deployment site (left) and instrument rack in-situ (right).
Time series results of ambient conditions for tidal height, temperature, and salinity are
given in figure 7. Temperature at the sensor level ranged from 23.1 to 29.1
o
C and salinity from
27.3 to 34.7 over the duration of the field test. The bottom panel displays the maximum difference
recorded between all reference thermistors mounted at the same depth but located across the
mooring rack. The average temperature difference observed across the space of the mooring rack
was 0.15 ±0.17
o
C, with a maximum of 1.23
o
C. Differences between instrument and reference
readings resulting from this variability should be minimized as the sampling bottle integrates
across the mooring space.
The HOBO U26 reported data throughout the entire deployment and generated 11296
observations based on its 15 minute sampling interval over the 17 week deployment. However,
only 11179 of the measurements were considered acceptable based on excluded values that were
more than 2 mg/L from reference samples over a similar timeframe. The accepted data resulted in
a data completion rate for this deployment of 99%. Time series results of the HOBO and
corresponding reference DO results are given in figure 8. Ambient DO measured by the HOBO
ranged from 2.07 to 15.92 mg/L while the range captured by reference samples was 3.630 to 9.851
mg/L. The average and standard deviation of the differences between instrument and reference
readings (limited to ± 2.0 mg/L DO; n=107 of 129 potential observations) were 0.090 ± .576 mg/L,
with a total range in the differences of -1.195 to 1.808 mg/L.
There was a small, but statistically
significant, drift in instrument offset (slope = 0.009 mg/L/d; r
2
= 0.18; p=0.009) throughout the