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Ref. No. [UMCES] CBL 2016-015
ACT VS16-06
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At the end of each mooring deployment a pre- and post-cleaned comparison of sensor
response to a 100 % saturated water bath was conducted. Upon retrieval the sensor was wrapped
in a damp towel and returned to the lab as quickly as possible. Prior to any cleaning, the sensor
was submerged in a 100 % DO water bath (via bubbling with air) and DO recorded for a minimum
of three readings after an initial 30 minute equilibration period. Then the sensor was removed
from the bath and cleaned of any visible biofouling according to recommended manufacturer
procedures. Following cleaning the sensor was submerged in a second 100% DO water bath to
avoid any biofouling debris carryover and DO recorded for a minimum of three readings after an
initial 30 minute equilibration period. Temperature of the both water baths was monitored
continuously and maintained at a constant condition within 0.5
o
C. DO concentration was
maintained at a constant saturated level with bubbling and confirmed by Winkler titration at the
beginning and final instrument reading timepoints.
Water-Column Profiling Test Procedures
Instruments were tested in a profiling application on a CTD rosette aboard the R/V
Laurentian in the Great Lakes. Profiling tests were conducted during strong thermal stratification
(late August, thermal gradient of >15 °C) and in two different regions including a normoxic and
hypoxic hypolimnion. The normoxic hypolimnion site was in Lake Michigan within a 100m deep
water column approximately 15 km offshore of Muskegon, MI. The hypoxic site profiling was
conducted in Muskegon Lake, a drowned river mouth lake adjacent to Lake Michigan.
Two full water-column CTD casts were conducted at each test site. The first trial involved
equilibrating test instruments at the surface (3m) for ten minutes and then collecting three Niskin
bottle samples at one minute intervals. Following the third sample, the rosette was quickly profiled
into the hypolimnion where samples were collected immediately upon arrival and then each minute
for the next 6 minutes. The second trial was performed in the reverse direction where instruments
were equilibrated for 10 minutes within the hypolimnion, three samples collected, and then
profiled into the surface and sampled at one minute intervals over the next 7 minutes
.
The CTD
was then immediately returned to the ship for sample processing. Triplicate BOD bottles were
filled from each Niskin and immediately fixed for Winkler titrations.
Reference Sample Analysis
The Winkler titration for quantifying dissolved oxygen was used as the standard for
comparison. The specific method is described in detail below and is based on the procedures
described in,
Measurement of primary production and community respiration in oligotrophic lakes
using the Winkler method
(Carignan et. al. 1998). All Winkler titrations were done at the
individual laboratory and field sites by trained ACT staff using standardized techniques and
equipment.
Initial Preparation
The volumes of each BOD bottles (≈ 125 mL) were determined with a precision better than
0.005%. The volume of each bottle was measured gravimetrically (± 0.01 mL) near 20
°
C, after
filling with degassed (boiled 10 min and cooled) distilled water. Since the procedure’s precision
approaches 1 µg O
2
·
L
-1
, particular care was taken to avoid contamination of the glassware and
working space from any trace amounts of thiosulfate, iodate, I
2
, and manganese. Reagents