Geoscience Reference
In-Depth Information
conducting cleaning procedures, inspect sampling equipment for signs of wear and tear
that may lead to sources of contamination and replace as required. All cleaning procedures
should be carried out in a designated area that does not have any airborne or other sources
of contamination. Cleaning procedures preferably should be performed in a clean labora-
tory environment while wearing appropriate safety wear and powderless polypropylene or
nitrile disposable gloves. Finally, all equipment cleaning procedures should be verified by
filling or passing laboratory-grade water through the equipment post the cleaning process
and analyzing for both fluorescence and absorbance.
4.2.4 Water Samplers
A description of the appropriateness for CDOM sampling of the numerous commercially
available water samplers is beyond the scope of this chapter; however, a number of general
points and a few specific examples are worth mentioning as they apply to a broad range of
sampling equipment. The initial sampling of water via any water sampler should be under-
taken with clean equipment that has been extensively rinsed/flushed with sample water
from that study site. This may mean pumping water through a submersible pump head
and tubing for a few minutes to flush the system or the collection of water on the upcast
after a CTD profile. Whatever sampler is used for water collection it should not be made
of materials as highlighted in
Section 4.2.1
, as these are likely to result in contamination
issues (e.g., use Nalgene but not nylon tubing). Water samplers specifically designed for
trace element work such as Niskin bottles (
Figure 4.2a
) or similar with silicone seals and
Teflon-coated springs are ideal. One attractive option if thoroughly cleaned before deploy-
ment in the field is the use of a GO-FLO water sampler (General Oceanics) (
Figure 4.2b
),
as these samplers operate on the close-open-close principle and thus pass the organic-rich
surface microlayer closed. This avoids contamination from the organic-rich surface micro-
layer and also any potential contamination from hydrocarbons from the research vessel. If
Niskin bottles or similar are used to collect water near the surface, care should also be taken
to avoid the surface microlayer. Discrete water samplers are commonly used in a number
of studies as they allow for water samples to be collected via an auto-sampler at a number
of time points without the investigator being present. With respect to DOM absorbance
and fluorescence analyses one drawback with the utilization of discrete water samplers is
modification of the optical characteristics of DOM may occur in the hold time of the water
between collection and subsequent analysis (see
Section 4.4
).
4.3 Sample Preservation
4.3.1 Filtration Techniques
Filtration directly after sample collection is recommended, as ongoing biological processes
may either cause an increase in CDOM via release from organisms (e.g., lysis, sloppy feed-
ing) or a decrease in CDOM due to metabolization by bacterioplankton. Filtration is also
