- Electrical Conductivity
Electrical Conductivity
Proxy for total solute concentration
~ Msmt of ability to pass electrical current through water
Higher E.C. --> Higher solute concentration
Solutes
= dissolved ions from chemical weathering
Higher solute concentration = higher e.c.
Application
Why solute conc matters?
- Chemical weathering in glacial envmts = important
Total erosion
Sequestering atmos CO2
- Info on glacial drainage systems
Solute conc tells of link btwn erosion rates & atmos CO2
Source: Water interaction with sediment + bedrock
E.C. vs Discharge
Inverse correlation btwn electrical conductivity & discharge (generally)
Subglacial meltwater E.C.
Subglacial meltwater has high EC ∴ high solute conc.
Why?
Meltwater interaction w rocks/sed at bed
Sediment = freshly ground & highly reactive
Fine sediment --> high surface area ∴ greater dissolution potential
Subglacial drainage system = critical
Channels
∴ Little time for solute interaction
Linked cavities
Route surface meltwater quickly
Route meltwater very slowly
Drainage type
More time for dissolution
Dictates time available for chemical reactions to occur
Seasonal evo solute conc (Gurnell 1992)
Start season
With increasing melt discharge
Solute concs = high
Since:
- discharge = low
- drainage = distributed
Solute conc decreases
Diurnal variability initiates
Solutes scale inversely with Q
i.e. high Q - low solute
Suspended sed seasonal evo
Suspended sediment increases with discharge
∴ E.C. & SSC exhibit
opposing response to discharge
Why E.C.
= useful
Separate proportion of bulk discharge routed via --> quick vs slow system
Assumes each system has characteristic EC
Then use bulk e.c. to determine relative contribution of each
Using E.C. to characterise bulk q
Collins @ Gornergletscher
Each system assigned a characteristic E.C.
Quick flow system
~10 µS/cm
Hydraulically efficient & channelised
Slow flow system
~ 40 µS/cm
Surrounding distributed
i.e. what's highest & lowest solute concs seen
∴ water routed out quickly
Separate proportion of bulk discharge routed via
--> distributed vs channelised system
Diurnal E.C. Decomposed (Richards 1996)
Early in season
Delayed flow dominates proportion of discharge
Low amplitude Q cycles
Through melt season
Quick flow increasingly dominant
During peak Q cycle = channelised
Only @ night does delayed flow dominate
Inefficient drainage
@ night when no melting
Haut Glacier d'Arolla