Sampling Flashcards
(26 cards)
What are the different methods for sampling water?
Surface water samples collected by hand from shore or small boats, or using ships underway pumping system.
Divers not used for water but sediment cores. Water bottles on CTD rosette for depth profiles.
What are the two types of bottles used for water samples?
Niskin and Go-Flo
Describe the Niskin bottle.
Most common method where the bottle enters the water open, simple and reliable.
Describe the Go-Flo bottle method.
Bottle passes surface interface, sent down closed, opens at ~10m and closes at required sampling depth.
What are the key requirements for using bottles for water sampling?
Rapid exchange with surrounding water, reliable closures, resistant to corrosion, no contamination, easy to handle (usually <10L).
How are bottles deployed on a hydroline?
Thin cable deployed from winch system, bottles are attached at set intervals, the bottles are closed using messengers (metal weights).
Pros and cons of bottle deployment using hydroline?
Simple
No knowledge of water column structure and unlikely line is vertical.
How are bottles deployed on a rosette?
Bottles attached to rosette, linked to the ship via a conducting cable, bottle closed individually by signal from ship.
Pros of bottles on a rosette?
Allows a preview of the water column structure, can sample specific features, large volumes obtained.
What are the sources of particles to water samples?
Biology, dust, rivers, resuspension in coastal/estuarine environments.
How do particle concentrations vary between environments?
Lower concentrations in the open ocean compared to turbid estuaries.
What size filter is used to separate the dissolved phase from the particulate phase in turbid estuaries?
0.75um
What should an ideal filter have?
High mechanical strength, uniform particle cut off and no contamination/absorption.
How should macronutrient samples be stored?
Freeze
How should trace metals samples be stored?
Acidify with HCl to pH~2
How should DOC/DON/DOP samples be stored?
Freeze or add mercuric chloride.
What are the benefits of in situ filtration of seawater?
Rapid deployment and recovery, allows collection of fine particles, can acquire a large mass of material.
What are the cons of in situ filtration of seawater?
Time series not possible, difficult to estimate particle fluxes, large particles may be missed.
What are the benefits of using sediment traps?
Direct flux measurements, time-series possible due to rotating collectors, large mass of material acquired, allows collection of rarer large particles.
What are the cons of using sediment traps?
Potential for over and under-trapping, swimmers and potential for microbial alteration of collected material, relatively expensive, poor at fine particle collection.
What are the limitations of ship-based sampling?
Limited spatial and temporal resolution, restricted by ship’s capabilities (water depth, ice, etc), expensive and time consuming, cannot sample ‘small’ features.
What is a key benefit of manned submersibles and ROV’s?
Allows precise sampling of small scale features.
How are communities mapped and monitored using ROVs and AUVs?
Multibeam sonar mapping for sea floor features, repeated surveys to assess environmental effects/change, imaging of the deep sea-floor (habitat mapping and MPA monitoring).
What are the benefits of using gliders?
Allows the characterisation of different water masses, data can be collected at high spatial and temporal resolution even in hostile conditions, can operate independently of ship, no need to retrieve as data is relayed to shore remotely.
