Water column sampling techniques

Question 1

What are the key requirements of water bottles for water sampling?

Answer 1

• rapid exchange with surrounding water
• reliable closures
• resistant to corrosion, no contamination
• easy to handle (usually <10L)

Question 2

What are the types of water bottle and what are their differences?

Answer 2

Niskin bottle, which is most commonly used, simple, reliable & enters water open.
However, the Go-Flo bottle is similar but passes the surface interface before opening at around 10m and closing again at the required sampling depth.

Question 3

What are the advantages & limitations of deployment of bottles on a hydroline?

Answer 3

Advantages: simple
Disadvantages: No knowledge of water column structure, line unlikely to be vertical

Thin cable deployed from system
Bottles attached at set intervals
Bottles closed using messengers (metal weights that slide down the line)

Question 4

What are the benefits of deployment of bottles on a rosette?

Answer 4

• obtain a preview of the water column structure
• can sample specific features (e.g. chlorophyll maximum)
• large volumes obtained by closing more than 1 bottle

Question 5

What sized filter is usually used to separate the dissolved phase from the particulate phase in the analysis of chemical constituents?

Answer 5

0.2 micron filter, but this is an arbitrary division.

Question 6

What makes an ideal filter?

Answer 6

• high mechanical strength
• uniform particle cutoff
• no contamination/adsorption

Question 7

What are advantages and limitations of sediment traps?

Answer 7

Advantages = Direct flux measurements, time-series possible via rotating collectors, can acquire a large mass of material, allows collection of rarer large particles

Limitations = potential for over and under-trapping, swimmers and potential for microbial alteration of collected material, relatively expensive and relatively poor at collecting fine particles

Question 8

What are the advantages and limitations of in situ pumps?

Answer 8

Advantages = rapid deployment & recovery, allows collection of fine particles, can acquire a large mass of material.

Limitations = time series not possible, difficult to estimate particle fluxes, large particles may be missed.

Question 9

Which collection method is best for collecting rarer large particles & enables time series measurements?

Answer 9

Sediment traps

Question 10

Which collection method is cheap, and simple to deploy and recover?

Answer 10

In situ filtration