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Ref. No. [UMCES] CBL 2016-014
ACT VS16-05
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mostly equilibrated by the third timepoint after transition but was somewhat variable in response.
For cast 3, the HL4 exhibited a slight initial positive offset during equilibration at the surface and
then showed an initial negative offset of -0.38 mg/L when rapidly transitioned to the colder, low
DO hypolimnion. The HL4 was again mostly equilibrated by the third sample after the transition.
The range in measurement differences between instrument and reference was -0.07 to 0.16 mg/L
for cast 2 and -0.38 to 0.11 mg/L for cast 3.
Results for the HACH HL4 for the two Lake Michigan trials are shown in figure 16. For
cast 1, the HL4 reached equilibration to surface DO concentrations and then showed an initial
positive offset (0.54mg/L) when rapidly transitioned to the cold high DO hypolimnion. The sensor
appeared to equilibrate after the third sample but continued to report a positive offset of
approximately 0.35 mg/L. For cast 2, there was a positive offset of 0.3 mg/L when equilibrated in
the hypolimnion and an initial negative offset when rapidly transitioned into the warm, normoxic
surface water. However, the sensor appeared to reach equilibration with surface concentration by
the final sample, 7 minutes after reaching the surface. The range in measurement differences
between instrument and reference was -0.05 to 0.54 mg/L for cast 1 and -0.14 to 0.32 mg/L for cast
2.
Figure 11
. Time series of the rosette profiling and Niskin bottle sampling for the two profiling trials in
Muskegon Lake.