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Ref. No. [UMCES] CBL 2016-013
ACT VS16-04
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below. The order of each sub-sample was recorded and tracked to examine any variation that arose
from sample handling. Approximately 10 - 12 independent sampling events were conducted each
week. At least once per week an intensive sampling event was conducted to capture the maximum
diurnal range of dissolved oxygen concentrations. Once per week field duplicates were collected
to examine fine-scale variability around the mooring site. Approximately 120 comparative
reference samples were collected over the 3 - 4 month-long deployments.
In conjunction with each water sample collection, each deployment site also recorded site-
specific conditions. The following information, logged on standardized datasheets were
transmitted electronically on a weekly basis to the ACT Chief Scientist, for data archiving and site
performance review:
•
Date, time (local) of water sample collection.
•
Barometric pressure from nearest weather station at time of water sample collection.
•
Weather conditions (e.g., haze, % cloud cover, rain, wind speed/direction) and air
temperature at time of water sample collection.
•
Recent large weather event or other potential natural or anthropogenic disturbances.
•
Tidal state and distance from bottom of sensor rack at time of water sample collection.
•
Any obvious problems or failures with instruments.
ACT was responsible for accurately characterizing temperature and salinity surrounding the
mooring with the goal of characterizing micro-stratification or heterogeneity surrounding the
mooring. Four RBR Solo temperature loggers and two SeaBird CTDs were deployed at each
mooring site. Sensors were mounted both at the instrument sampling depth and approximately 0.5
m above the sampling depth
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.