Ab t t # 166623
Abstract
W tl d Forest
Wetland-Forest
Wetland
F
t Transition
T
iti att the
th Edge
Edg off P
Permafrost:
f
t Roles
R l off Water
W t and
d Energy
E
gy Transport
T
p t Process
P
1Dept.
D t
Dept
off Geoscience
G
Geoscience,
i
U
Univ
Univ.
i off C
Calgary
Calgary,
l
Calgary
Calgary,
C l
Alberta
Alberta,
Alb t Canada;
C
d
1 Introduction
1.
I t d ti
Willi
William
L.
L
2Dept.
D t
Dept
2
Quinton
Q i t
,
Questions:1) How will the permafrost distribution change with the warming?
2) How does vegetation influence the thawing of permafrost?
3)) What
Wh t are the
th eco-hydrological
eco hydrological
hyd l gi l iimplications
pli ti
off permafrost
p
f
t thaw?
th ?
Th frost
The
f t table
t bl is
i generally
g
lly deep
d p under
d topographic
t p g phi lows
l
(Fig
(Fig.
(Fi
( g 5b).
5b)) The
Th lowering
l
i g off
th ffrostt table
the
t bl was much
h faster
f t in
i the
th Centre
C t than
th the
th West
W t site
it (Fig.
(Fig
((Fig 6a).
6
6a)) Th
The Centre
C t
site is in a depression (Fig.
(Fig 5b) and has a wet condition (Fig.
(Fig 6b) due to subsurface
flow convergence,
convergence whereas the West site is higher and has a dryer condition.
condition
• Annual
A
l ffrostt ttable
bl ((FT)) surveys
y on a transect
t
t
across a permafrost
p
f t plateau
pl t
(Fig
((Fig.
(Fig 4)) since
i
1999.
1999
COLOR SCALE
NEEDED
(W i ht ett al
(Wright
al.,
l 2009.
2009 Water
W t Resour.
R
Resour
R
Res
Res. 45,
45 W05414)
• Four meteorological stations near FT transect
transect.
((Wright
g et al
al.,, 2009))
• Soil
S temperature/moisture
p
/
monitoring
g stations
stations.
• High
High resolution
High-resolution
l ti (4
( m)) satellite
t llit image
i g in
i 2000
2000.
(H
(Hayashi
hi ett al.,
l 2004.
2004 J.
J Hydrol.,
H d l 296:
296 81
81-97)
97)
• High
High-resolution
resolution (1 m) LiDAR survey in 2008.
2008
((Quinton et al
al.,, 2009,
2009, Can.
Can Water Resour.
Resour JJ.,, in press)
p
)
S tt
Scotty
Creek
• Electrical
El t i l resistivity
i ti ity imaging
i gi g (ERI)
(
) in
i 2009
2009.
fen
Fig.
Fig
g 6 (a) Depth
ept to the
t e frost
ost table
tab e
((FT)) at Centre and West soil
monitoring
it i g site
it (see
(
Fig
Fi
Fig.
g 5b)) in
i 2004
2004.
Ob
Observed
dd
data
t ((symbols)
b l ) are based
b
d
on frost
frost-probe
f t probe
b measurements
t and
d
soil temperature monitoring,
monitoring and
lines show simulated frost table
using
g a vertical heat transfer
f model
model.
(b) Liquid
Li id volumetric
l
t i water
t content
t t
att 0
0.2
2-m
2md
depth
th (Hayashi
(H
hi ett al
al.,
l 2007)
2007).
elev.
elev
l
((m))
permafrost
p
plateau
l t
1000 kkm
bog
g
ERI2
271
Fig.
Fig
g 4 Studyy areas in the Scottyy Creek watershed
watershed.
F t t bl survey
Frost-table
y ttransectt ((FT)
(FT),
) ffrost-table
t t bl
mapping
i plot
l t (PLT)
(PLT), and
d electrical
l t i l resistivity
i ti it
imaging (ERI) lines are shown.
shown
26
267
C ti
Continuous
((> 90%)
Di
Discontinuous
ti
(50
(50-90%)
90%)
Discontinuous (10
(10-50%)
50%)
Isolated patches
p
(<
( 10%))
No permafrost
p
Fig
Fig.
g 1 Permafrost distribution in Canada.
Canada
(
(Nat
(Natural
ral Resources
Reso rces Canada,
Canada, http
http://atlas.nrcan.gc.ca/site/
p //atlas nrcan gc
g ca/site/
english/maps/en
english/maps/environment/land/permafrost)
g
p
ironment/land/permafrost)
p
)
Fig 2 Scotty Creek represents typical peatlands in
Fig.
the Northwest Territories.
Territories Discontinuous permafrost
occurs as a mosaic of non
non-permafrost
permafrost wetlands and
p
permafrost
p
f
p
plateaus
l
that
h supports
pp
trees The
trees.
Th
th i off permafrost
thawing
f t may causes a major
j change
h
i landscape
in
l d
and
d hydrological
h d l i l pathways.
pathways
th
2 Study
2.
S
y Site
S – Scotty
S
yC
Creek Research Basin
Scotty Creek is in the Northwest Territories (NWT) of Canada (Fig.
(Fig 1)
1), and is
covered
d with
ith a thick
thi k (2-3
(2
( 3 m)) layer
l y off peat.
peat
p t
Th
Three
di
distinct
ti t llandcover
d
typ with
types
ith different
diff
t hydrological
hyd l gi l functions
f
ti
exist
i t as a
complex
pl mosaic
i (Fig
(Fi
((Fig.
g 2)
2):
)
4 Results:
4a
4a.
R
lt Frost
F
t Table
T bl Dynamics
Dy
i
A
Annual
l frost
f t surveys
y on the
th same line
li everyy year
y
in
i the
th permafrost
p
f t plateau
pl t
(Fig
(Fig.
((Fig 4))
revealed a steady shrinkage of plateau due to the lateral thawing from both sides
(Fig 5a) Elevation surveys from 2006 and 2009 indicate that the plateau is
(Fig.5a).
subsiding
b idi g as the
th active
ti layer
l y deepens
d
(Fig
(Fi
((Fig.
g 5b).
5b))
Thi results
This
lt in
i the
th encroachment
h
t off fens
f
and
d bogs
b g into
i t black
bl k
spruce
p
fforestt ((Fi
(Fig
(Fig.
g 5c).
5
5c)) A
As the
th trees
t
die
di and
d fall,
fall
f ll, the
th plateau
pl t
edges are exposed to radiation inputs and the contact with
relatively warm surface water in the wetlands
wetlands, thereby
sustaining
t i i g the
th continued
ti
d shrinkage
h i k g off permafrost
f t and
d
expansion
p
i off non-permafrost
non-permafrost.
p
f t
((1)) Permafrost
P
f
t plateaus
pl t
rise
i 1
1-2
2 m above
b
the
th surrounding
di g wetlands
tl d and
d generate
g
t
runoff that feeds fens and bogs (Fig.
(Fig 3)
3). They support black spruce forests
forests.
Thawing of permafrost plateaus may change the relative proportion of forests and
wetlands
wetlands,
tl d and
d connectivity
ti ity off hydrological
hyd l gi l pathways
p
pathways.
th y
Fig.
Fi
Fig
g 3 Schematic
S h
ti cross section
ti off a
permafrost
f t plateau.
plateau
l t
Th
The active
ti llayer
de elops during
develops
d ring summer
s mmer months.
months
Snowmelt and storm runoff mainly
occur as subsurface flow (blue
(
arrows)) through
h gh the
h saturated
d zone
within
ithi the
th active
ti layer.
layer
l
The
Th plateau
l t
is
i
surrounded
d db
by b
bogs or ffens
fens.
40
30
( )
(a)
20
1999
f
frozen
peat
p t
rre
ela
ativ
ve
ee
ele
ev
e
va
attio
on
n ((m
m)
m)
((3)) Flat
Fl t b
bogs
g store
t
water
t and
d occasionally
i
lly drain
d i to
t channel
h
l fens.
fens
f
They
Th y are
d i t d by
dominated
by Sphagnum
Sph g
moss and
d contain
t i acidic
idi water.
water
t
ttrra
an
ns
se
ec
ctt le
en
ng
gtth
h ((m
m)
m
(2) Channel fens provide drainage network
network, and support vascular aquatic plants
plants.
((b))
C t
Centre
0 5 2006 GS
0.5
0
2009 GS
2006 FT
-0.5
05
0.5
2009 FT
-1
1
-1
-1.5
15
2002
2005
year
2008
0
10
20
30
40
h i
horizontal
t l distance
di t
(m)
( )
Fig 5 (a) Length of the annual frost table (FT) survey transect indicating the lateral shrinkage
Fig.
of permafrost.
permafrost
p
((b)) Elevation of the ground
g
surface ((GS)) and the FT surveyed
y in the late August
g
of 2006 and 2009 showing
g the lateral shrinkage
g of permafrost
p
(red
(
arrows)) and the deepening
p
g
off the
th active
ti layer.
layer
l y Elevation
El
ti is
i measured
d relative
l ti to
t a stable
t bl datum
d t
anchored
h d to
t the
th mineral
i
l
soilil Blue
soil.
Bl arrows show
h
the
th location
l
ti off soilil monitoring
it i instrumentation
i t
t ti sites
sites.
it
(c)
( ) A 2008
photograph of a monitoring station,
station which had been located inland but was nearly submerged.
submerged
clearing
l i
f
forest
t
Fig. 9 Resistivity
Fi
Fig
R i ti it image
i
for
f ERI2
0m
24
0m
in Fig.
Fig 4,
4 obtained with 3
3-m
m
5
electrode spacing.
spacing The frost table
permafrost
p
((FT)) under the road clearing
g was 10
d t
determined
i d using
i g a hand
h d auger.
auger
g
48
FT
partial
p
th i ?
thawing?
72
f
forest
t
96
permafrost
p
15
resistivity
es st ty (Ω
( m))
10
102
103
104
The high-resolution
high resolution satellite image from 2000 and the
LiDAR d
data
t ffrom 2008 were used
d to
t delineate
d li
t the
th
di t ib ti off p
distribution
permafrost
f t plateaus
pl t
and
d wetlands
wetlands.
tl d
02
0.2
04
0.4
0.8
0
8
06
0.6
04
0.4
02
0.2
0
W t
West
Centre
(a)
(b)
Figure
gu e 10
0 sshows
o s the
e 2008
008 extent
e e of
o plateaus
p a eaus in brown
bo
and
a d
the loss of plateau areas during 2000-2008
2000 2008 in red.
red Clearly
Clearly,
permafrost plateaus
platea s are tha
thawing
ing from the edges
edges, which
hich is
consistent
i t t with
ith the
th interpretation
i t p t ti off the
th ERI data
d
data.
t
C t
Centre
W t
West
5/1
5/16
5/31
6/15
6/30
7/15
7/30
8/14
Fi 7 Frost
Fig.
F t table
Frost-table
t bl elevation
l
ti iin a detailed
d t il d
elev ((m))
elev.
survey plot (PLT in Fig.
Fig 4) in June 2006,
2006
measured on 0
0.25-m
25 m grids
g
and interpolated
p
byy krigging
gg g ((Wright
g et al
al., 2009)). Elevation is
relative
l ti to
t an arbitrary
bit y datum.
d
datum
t
Th
The colors
l
i di t th
indiate
the thickness
thi k
off the
th saturated
t t d zone
within the active layer after a 15
15-mm
mm rain
event, simulated using
event,
g a two
two-dimensional
dimensional
flow model.
model The frost table represents
p
an
i p
impermeable
bl b
boundary
d y off unconfined
fi d
aquifer
aquifer,
if which
hi h evolves
l
during
d i a thawing
th i
simulated thickness of
season
season.
Fig 8 Resistivity image for ERI1 0 m
Fig.
in Fig.
Fig
g 4.
4 (a)
( ) Image
g obtained with
5
3 m electrode spacing,
3-m
spacing
p
g, showing
g
th clear
the
l
definition
d fi iti off the
th
10
permafrost
f tb
bottom.
bottom
tt
(b) IImage with
ith
15 ((a))
1-m
1
m electrode spacing showing the
details including the deepening of
details,
the active layer
y below a depression
depression.
p
F
Fen
24
100 m
Fi 10 Permafrost
Fig.
P
f t
degradation (shown in
red)) between 2000 and
2008 ((Quinton et al
al.,, 2009)
2009).
)
The peat-covered,
peat covered,
covered discontinuous permafrost of Scotty Creek watershed is thawing
with
ith the
th climate
li t warming,
warming
i g which
hi h is
i consistent
i t t with
ith model
d l prediction
di ti in
i the
th literature
lit
literature.
t
Resistivity survey along ERI1 (see Fig.
Fig 4) clearly delineated permafrost under the
peatt plateau
p
pl t
(Fig
(Fig.
((Fig 8a)
8 ) . ERI was also
l effective
ff ti for
f delineating
d li
ti g the
th peat/clay
p t/ l y boundary
boundary,
b
d y
which
hi h was confirmed
fi
d using
i g a hand
h d auger
auger.
g The
Th sharp
sharp,
h p, vertical
ti l boundary
b
d y between
b t
the
th
permafrost and adjacent wetlands may indicate the importance of lateral heat
transfer . The high-resolution
high resolution survey showed the deepening of the active layer under
a depression
d p
i (Fig
(Fig.
(Fi
( g 8b),
8b)) p
providing
idi g ffurther
th evidence
id
for
f the
th feedback
f db k mechanism.
mechanism
h i
0m
Si
Since
th
the permafrost
p
f t degradation
d g d ti is
i occurring
i g both
b th laterally
l t lly
and vertically
vertically, it is very important to consider the lateral
heat transfer and the water-energy
water energy feedback processes at
a “sub-grid”
“sub
bg
grid
id” scale
l (i
(i.e.
( e 100-1
100 1,000
1 000 m)) in
i modelling
d lli g off
climate-permafrost
li t p
f t interaction
i t
ti in
i the
th discontinuous
di
ti
permafrost
p
f
regions
regions.
gi
5 Conclusions
5.
4b Results:
4b.
R
lt Permafrost
P
f
t Imaging
I gi g and
d Mapping
M ppi g
West
ERI was also
l conducted
d t d across a winter
i t road
d (ERI2
(
in
i Fig.
Fig 4)) to
Fig
t examine
i th
the effects
ff t
of canopy
py removal
removal,, which took place
p
in the1950’s
the1950 s . The active layer
y was much
deeper (ca.
(ca 2.5
2 5 m) under the road cut
cut, and relatively low resistivity indicates the
presence of liquid
liq id water
ater in the permafrost underneath
nderneath (Fig
(Fig. 9)
9). The ground
gro nd ssurface
rface
h subsided
has
b id d along
l g the
th road
d cutt due
d to
t the
th deepening
d p i g off the
th active
ti layer
layer.
l y
0
saturated
t t d zone (m)
( )
((c))
1
Th thermal
The
th
l conductivity
d ti ity off peatt is
i strongly
t gly dependent
d
d t on water
t content
t t as water
t is
i
much
h more conductive
d ti than
th air
i and
d organic
g i material
material.
t i l Enhanced
E h
d deepening
d p i g off the
th
active
i layer
l y under
d depressions
d p
i
is
i due
d to the
h positive
p i i feedback
ffeedback,
db k, in
i which
hi h the
h
convergence of water during thawing seasons enhances the vertical heat conduction
conduction.
This concept is demonstrated on a detailed frost
frost-table
table map (Fig.
(Fig 7)
7), surveyed on a
rectangular
t g l plot
pl t (PLT
(
in
i Fig.
Fig 4)) in
Fig
i June
J
2006.
2006 A ttwo
two-dimensional
di
dimensional
i
l flow
fl
model
d l based
b
d on
th Dupuit-Forchheimer
the
D p it F hh i
equation
q ti was used
d to
t simulate
i l t the
th distribution
di t ib ti off the
th
saturated
sa
u a ed thickness
c ess in the
e active
ac e layer
aye after
a e a hypothetical
ypo e ca rainfall
a a of
o 15
5 mm
mm. The
e
model shows thicker saturated zones in the areas of deeper frost table (Fig.
(Fig 7)
7).
PLT
ERI1
FT
(Hayashi et al
al., 2007
2007. Hydrol.
Hydrol Process
Process. 21: 2610-2622)
E-mail:
E
mail:
il h
hayashi@ucalgary
hayashi@ucalgary.ca
y hi@
@
lg y ca
off Geography
G
h and
d Environmental
E i
t l Studies,
Studies
St di
Wilf id Laurier
Wilfrid
L i Univ.,
Univ
U i Waterloo,
Waterloo
W t l
Ontario
Ontario,
O t i Canada
C
Canada.
d
3 Methodology
3.
M th d l gy
The
e permafrost
pe a os region
eg o of
o Canada
Ca ada (Fig
((Fig.
g 1)) iss o
one
eo
of the
e most
os rapidly
ap d y warming
a
g
regions on the planet . Large
Large-scale
scale modelling studies predict pole-ward
pole ward shift of the
discontin o s permafrost zone
discontinuous
one due
d e to the warming
arming (e.g.
( g Delisle,
(e
D li l 2007.
Delisle
2007 Geophys.
G
Geophys
h
R
Res
Res. Lett.,
L tt 34
Lett
34,
L09503)). This
Thi mayy cause major
j changes
h g in
i the
th di
distribution
t ib ti off p
permafrost
f t within
ithi the
th
di
discontinuous
ti
p
permafrost
f t zone (Fig.
(Fig
((Fig 2)
2).
)
Laura
L
2
Chasmer
Ch
eptth
h (m)
m)
liq.
q wate
a err co
con
nt.. FT dep
M
Masaki
ki
1
Hayashi
H y hi ,
48
Pl t
Plateau
B g
72 Bog
unfrozen peat
p
permafrost
96
However,, the
H
However
th thawing
th i g does
d
nott occur as a resultlt off uniform
if
reduction
d ti in
i thickness
thi k
as
assumed
d in
i large
large-scale,
l g scale
l , vertical
i l model
model.
d l It
I occurs as:
- Preferential deepening of the active layer in topographic depressions.
depressions
- Shrinkage at the edges of plateaus due to the exposure to radiation and the lateral
h t ttransfer
heat
f from
f
the
th neighbouring
ighb i g wetlands
wetlands.
tl d
- Thawing
Th i g along
l g th
the lilines off canopy
py removall (roads
((roads,
d , seismic
i i cutlines)
cutlines).
tli
)
In all
a these
ese cases,
cases the
e pos
positive
e feedback
eedbac between
be ee water
a e and
a de
energy
e gy transfer
a s e sus
sustains
a s
progressive thawing.
thawing
Effects of these sub-grid
ssub
b grid scale processes
processes, and impacts of local disturbances
dist rbances need to
b considered
be
id d iin ffuture
t
modelling
d lli g efforts
efforts.
ff t
clay
l y
A k
Acknowledgements
l dg
t
0
depression
40
30
50
60
2
4 ((b))
resistivity (Ω m)
10
102
103
104
F di
Funding:
C
Canadian
di Foundation
F
d ti for
f Climate
Cli t and
d Atmospheric
At
h i Science
S i
(IP3 Network)
N
Network),
t
k) International
I t
ti
l
Polar Year,
Year Natural Sciences and Engineering Research Council,
Council Northern Scientific Training
Program
Program,
g
, Environment Canada Science Horizons Program
Program.
g
Field work: Nicole Wright,
Wright
g , Mike
T
Toews
Toews,
T
Trevor
Myers
Myers,
M
Larry
L
Bentley,
Bentley
B tl Alastair
Al t i M
McClymont,
McClymont
Cl
t Brendan
B d Christensen,
Ch
Christensen
i t
Tyler
T l Veness.
V
Veness
Logistics:
g
Water Surveyy of Canada
Canada,, Liidlii Kue First Nation
Nation.