Field Sampling Using
the Rosette Sampler
Glenn J. Warren
U.S. Environmental Protection Agency
Great Lakes National Program Office
77 West Jackson Boulevard
Chicago, IL 60604
May 1996
-------
Field Sampling Using the Rosette Sampler
1.0 Rosette Sampler
The Rosette sampler is the primary sampling instrument for the collection of all Nutrient
parameters, phytoplankton, chlorophyll a, phaeophytin a, and dissolved oxygen from the
Biological Category, and temperature, total suspended solids, turbidity, specific
conductance, and pH from the Physical Category.
A 12-bottle Rosette sampler system (Sea-Bird Electronics 32 Carousel Water Sampler)
will be used to collect water samples. This equipment allows an operator to remotely
actuate a sequence of up to 12 water sampling bottles. This system consists of a CTD
(conductivity, temperature and depth sensor - Sea-Bird Electronics Model 9 Underwater
Unit) attached at the bottom of the Rosette, an A-frame, 1000 feet of multi-conductor
cable, a variable speed winch and Sea-Bird Electronics Model 11 Deck Unit with attached
computer. The CTD measures water depth and temperature, which is graphically (CRT)
displayed onboard the research vessel. The bottles can be closed in any predetermined
order, remotely from the deck of the vessel while the array is submerged at the various
sampling depths. The Rosette sampler is equipped with 8 L Niskin bottles.
The depth at which samples will be collected is detected by a pressure transducer on the
CTD. To assure that the display parameters are set to include the entire water column, the
Rosette winch operator obtains a depth sounding from the bridge and writes this on the
Rosette form, then adjusts the computer program parameters controlling the depth range to
be displayed (See "Instructions for use of the Sea-Bird 9/11+..."). The Rosette sampler
will then be lowered to the bottom at between .5 and 1 meter/second, raised at least 5
meters after contacting the bottom. The operator will wait three minutes to allow the
sampler to drift away from the disturbed area before the B-2 (2 meters up from the
bottom) sample is taken. The Rosette sampler will be lowered to B-2 and the sample
taken.
Additional time intervals of three minutes are allowed to elapse prior to taking the
thermocline sample and the lower epilimnion sample. These intervals provide time for
water equilibration within the Niskins.
The knees of the EBT temperature depth trace will be determined by trisecting the angle
between the epilimnion and mesolimnion temperature traces (upper knee) and the angle
between the mesolimnion and hypolimnion temperature traces (lower knee). The upper
knee is the upper a angle intercept, the lower knee is the lower a angle intercept. The
lower epilimnion sample is one meter above the upper knee. The upper hypolimnion
sample is one meter below the lower knee.
1-186
-------
Field Sampling Using
Volume 1, Chapter 2 the Rosette Sampler
2.0 Sequence of Sampling Events
The following is a brief summary of the sampling events. Some events may be done
simultaneously and event order will be subject to conditions.
2.1 Visual and Physical Station Observations
Air temperature, wind speed, aesthetics, wind direction, depth, and wave height.
2.2 Rosette Sampling
Run Rosette/CTD down to define the temperature profile and determine the thermocline
location during stratified situations. Examine the CTD profile. Select sampling depths
according to depth selection. Trigger sample bottle at correct depths, while verifying the
temperature profile Split Rosette Niskin samples into the required sample
bottles/preservatives. A composite 20 m sample is taken for phytoplankton, chlorophyll a,
pheophytin, and, when appropriate, primary productivity, by compositing Niskin samples
at 1, 5, 10 and 20 meters.
3.0 Sample Integrity
Concentrations of chemicals in lake water are very dilute. A small amount of sample
contamination can have a large effect on the results. Avoiding contamination is, therefore,
a major quality control goal. Each Niskin sampling bottle shall be emptied into the sample
bottles as soon as possible. All chemistry sample bottles shall be rinsed once with sample
before filling. New 1 g polyethylene containers (PEC) will be used to hold the sample for
the on board analyses and preparations.
One gallon polyethylene containers filled directly from Niskin sampling bottles are used for
nutrients, pH, specific conductance, alkalinity and turbidity analyses. Samples for
analysis of dissolved nutrients are taken from the 1 g containers and filtered into new
125 mL sample bottles.
Samples for chlorophyll a analysis are collected directly from Niskin sampling bottles into
300 mL brown polyethylene sampling bottles. Water to be used for primary productivity
analysis taken directly from Niskin sampling bottles into 960 mL polyethylene bottles.
These samples are composited into brown, 4 L polyethylene bottles.
To reduce contamination from atmospheric dust, empty bottles will be capped during
preparation for sampling. Care should also be taken in the storage of bottles to reduce
exposure to "dirty" environmental conditions. During sampling, each bottle is rinsed with
sample water, emptied, and filled with sample water. The cap is replaced after addition of
the preservative, or immediately on samples that require no preservative. Transfer of the
samples from one container to another or manipulations of the sample are avoided as much
as possible since each such action can result in contamination.
1-187
-------
Field Sampling Using
the Rosette Sampler Volume 1, Chapter 2
To reduce contamination and to control the volume of the preservatives, automatic pipettes
or dispensers are used to dispense all preservatives. Prevention of inadvertent use of the
wrong preservative is accomplished by the use of the same color tag on the sample bottle
and preservative dispenser. Dissolved oxygen samples are "set up" immediately. This
involves filling the bottle to overflowing, allowing overflowing to continue five seconds
before adding, in series, the first two reagents, allowing the floe to settle, mixing and
allowing floe to settle again. D.O. samples are then completed in the main laboratory.
4.0 Nutrient Sample Filtration
A number of samples must be filtered, after sample splitting. The following are brief
summaries. Dissolved nutrient samples will be prepared by vacuum filtration (<7 psi) of
an aliquot from the PEC for onboard analyses within an hour of sample collection. A
47 mm diameter 0.45 (jm membrane filter (Sartorius) held in a polycarbonate filter holder
(Gelman magnetic) with a polypropylene filter flask prewashed with 100 to 200 mL of
demineralized water or sample water will be used. New 125 mL polyethylene sample
bottles with linerless closures will be rinsed once with filtered sample prior to filling.
5.0 Instructions for Use of Sea Bird 9/11+ and Rosette for
Collection of Water Samples and Cast Information
The SeaBird 9/11+ is built to provide real time information on a number of water quality
parameters as it moves through the water. The software used to run the instrument and
collect data (Seasave) has been configured for generalized sampling conditions.
Depending on the depth and expected values of the parameters, the configuration will
likely require modifications.
The Dolch computer in the Rosette control room is loaded with the software to run the
SeaBird 9/11+. After turning on the computer, go to the C:\SEA911 subdirectory. Enter
the Seasave program by typing Seasave. The first screen that you see will give you
choices on whether to Acquire Real Time Data or to Display Archived Data. Highlight the
"Acquire..." option and press . The next screen will require verification that the
data will be written to disk, as well as the entry of a file name for the data to be acquired.
After these are entered, highlight the "XY parameters to be plotted" and make sure that the
ranges for depth, temp, etc. are appropriate for the station. After making any necessary
changes, you exit from this screen by pressing . At this point (or before) turn on
the SeaBird deck unit. Press to begin acquiring data. Next you will see a header
information screen. At a minimum, enter the station number. You may enter the position
(latitude & longitude) information and any notes that you have about the station. After
exiting this screen (by following the instructions on the screen), the program will delay
slightly to initialize the rosette, and a graph will be displayed with function key menus on
the top and bottom of the graph.
Remove the PAR sensor cover, remove the buffer bottle from the pH probe, and remove
the Tygon tubing (GENTLY!) from the temperature probe. Deploy the SeaBird Rosette.
Keep the Rosette just under the surface of the water for one minute, then turn on the pump
by entering . Wait another minute and then begin the cast. If the altimeter is
1-188
-------
Field Sampling Using
Volume 1, Chapter 2 the Rosette Sampler
working, stop the Rosette 1-2 meters off the bottom. If it is not working, let the Rosette
touch bottom, then raise it to 5 meters off the bottom. Determine the sample depths and
mark them on a data sheet. If the deepest sample will be below 5 meters off the bottom,
wait two minutes before taking the sample. Otherwise begin sampling as the Rosette is
raised. Bottles are fired by entering . A number will appear in the upper
right hand of the screen when the bottle has fired. Continue taking samples until the
Rosette reaches the surface. Take the surface sample, if required, then turn off the pump
by entering . Exit the Seasave program by entering , and turn
off the deck unit. Bring the Rosette onto the deck. Cover the PAR sensor, return the
buffer bottle to the pH probe, return the Tygon tubing to the end of the temperature probe,
and fill this with deionized water.
Exit completely from the Seasave program, until you see the C:\SEA911 prompt. Place a
formatted disk in the A: drive of the Dolch. Enter " castproc filename", where filename is
the file with the freshly gathered data. The data will be processed and copied to the A:
disk. Take this disk into the wet lab and place it in the A: drive of the Compaq LTE Lite.
From the Windows screen select the SeaBird icon, then the Seaplot icon. Once in Seaplot,
make sure the file of interest is the one to be used by the program. Modify the parameter
ranges to coincide with those of the station, and run Seaplot. This will graph the data for
display.
1-189
-------
Field Sampling Using
the Rosette Sampler
Volume 1, Chapter 2
Appendix A. Sample Log
U.S. EPA The R/V LAKE GUARDIAN 19
STATION DATA SHEET - SEABIRD 9/11+ AND ROSETTE
DATE
GMT
LAKE
STATION
QA DEPTH: FIELD DUP(D)
SONAR (BRIDGE) DEPTH _
WEATHER
LATITUDE
LAB SPLIT(C)_
AIR TEMP.
SEA STATE
LONGITUDE
SURFACE WATER TEMP.
PERSONNEL: ROSETTE
SECCHIDEPTH
NET
OTHER
Sample
Number
Bottle
Number
Depth Code
Use (S,D,I)
Depth
Profile Code
1-190
------- |