1. 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?

  1. Chemical weathering in glacial envmts = important

Total erosion

Sequestering atmos CO2

  1. 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