Role of permafrost in wetland formation
•Alaska which has 174.7 million acres of wetland.
•Permafrost is responsible for this large amount of wetland.
•Alaska has about 63% of the US’s remaining wetlands.
Source: Academy for Advancement of Science and Technology
Tundra: A treeless area between the icecap and the tree line of
Arctic regions, having a permanently frozen subsoil and
supporting low-growing vegetation such as lichens, mosses,
and stunted shrubs.
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Arctic Circle: imaginary circle on the surface of the earth at 66 1/2°N
latitude, i.e., 23 1/2° south of the North Pole. It marks the
northernmost point at which the sun can be seen at the winter solstice
(about Dec. 22) and the southernmost point of the northern polar
regions at which the midnight sun is visible.
Frost : A deposit of minute ice crystals formed when water
vapor condenses at a temperature below freezing.
Permafrost: Permanently frozen subsoil, occurring throughout
the Polar Regions and locally in perennially frigid areas.
Arctic: A region between the North Pole and the northern
timberlines of North America and Eurasia.
SubArtic: Of or resembling regions just south of the Arctic
Circle.
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Temperate: Characterized by moderate temperatures,
weather, or climate; neither hot nor cold.
Ice vs. Snow: Falling ice composed of crystals in
complex hexagonal forms. Snow forms mainly when
water vapor turns directly to ice without going through
the liquid stage, a process called sublimation.
Thaw: To change from a frozen solid to a liquid by
gradual warming.
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Anomalous behavior of water
Source: http://www.sbu.ac.uk/water/
Consequences of water’s density anomaly:
•the necessity that all of a body of water (not just its surface) is
close to 0°C before any freezing can occur,
• the freezing of rivers, lakes and oceans is from the top down, so
insulating the water from further freezing and allowing rapid
thawing,
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The Role of permafrost and seasonal
frost in hydrology of northern wetlands
in North America.
Ming-Ko Woo and Thomas Winter
Some Review Questions:
• What is the climatic variable of most interest?
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Some Review Questions:
• What is the climatic variable of most interest?
Difference between precipitation and evapotranspiraton.
Some Review Questions:
• What is the Boreal zone as denoted in the paper?
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Some Review Questions:
• What is the Boreal zone as denoted in the paper?
Southern fringe of the SubAcrtic
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Some Review Questions:
•What is the precipitation trend for our region of interest?
Some Review Questions:
•What is the precipitation trend for our region of interest?
Increases in South-Easterly direction.
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Some Review Questions:
•From the following “hydroperiod” graph, identify where this wetland
is located a) Arctic, b) SubArctic, c) Temperate region ?
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Some Review Questions:
•From the following “hydroperiod” graph, identify where this wetland
is located a) Arctic, b) SubArctic, c) Temperate region ?
Cold Arctic. Indicated by the permafrost layer starting
less than a meter depth.
Some Review Questions:
•From the following “hydroperiod” graph, identify where this wetland
is located a) Arctic, b) SubArctic, c) Temperate region ?
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Some Review Questions:
•From the following “hydroperiod” graph, identify where this wetland
is located a) Arctic, b) SubArctic, c) Temperate region ?
Temperate region. Depth of seasonal frost is very less.
In some periods of the winter, soil does not freeze at all.
Some Review Questions:
•Where there is no permafrost, which of these have a thicker layer of
seasonal frost and why : a) wetlands, b) mineral-soil terrain ?
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Some Review Questions:
•Where there is no permafrost, which of these have a thicker layer of
seasonal frost and why : a) wetlands, b) mineral-soil terrain ?
The Mineral-soil terrain has a thicker layer of seasonal frost.
a) thermal conductivity of soil > wetland.
b) more latent heat of dissipation required to freeze in
wetland.
Some Review Questions:
• In spring, where is thawing rate faster, a) wetlands, b) mineral-soil
terrain ?
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Some Review Questions:
• In spring, where is thawing rate faster, a) wetlands, b) mineral-soil
terrain ?
Mineral-soil terrain
Some Review Questions:
• In the Boreal zone, it is found that the rate of thawing is more beneath
the frost layer, Why?
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Some Review Questions:
• In the Boreal zone, it is found that the rate of thawing is more beneath
the frost layer, Why?
Because of heat exchange between ground water and peat.
Some Review Questions:
• What is Aufeis ?
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Some Review Questions:
• What is Aufeis ?
Ground water seepage normally freezes as it encounters the
cold air at the ground surface creating a layer of ice called Aufeis.
Some Review Questions:
•Can water infiltrate into frozen wetland soils?
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Some Review Questions:
•Can water infiltrate into frozen wetland soils?
Yes. As soil gets colder, water freezes and closes the
pores, decreasing vertical hydraulic conductivity.
Comparison of trends in precipitation and surface runoff
Runoff ratio = (mean annual runoff)/(mean annual precipitation)
Ratio = 1
all ppt flowing over land
Ratio = 0
ppt either stored in land or evaporated.
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Comparison of trends in precipitation and surface runoff
Precipitation trend
Figure 2
Ppt - Evap.
Figure 3
Runoff Ratio trend
Figure 7
Processes behind overland flow
Hortonian overland flow:
An overland flow of water occurring more or less
simultaneously over a drainage basin when rainfall exceeds
the infiltration capacity of the basin.
Saturation Excess Overland Flow:
It is precipitation that cannot be absorbed by the soil
because the soil is already saturated with water, so it
flows across the land surface to a stream or other body
of water
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Question ??
• In areas of permafrost, spring period is characterized by
thawing snow unable to infiltrate the permafrost layer and
flowing over the land surface.
What kind of overland flow do you classify this as and why?
The spring season and sudden burst of activity.
Accumulated snow melts.
Soil remains frozen.
Water cannot infiltrate.
Water flows towards depressions.
Water collects in wetlands.
Source: San Diego Zoo
Water even crosses drainage divides.
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Wetland-Subsurface water interaction
Example 5(A) from Lone Gull, Keewatin.
Areas of permafrost, permafrost serves as confining bed
for shallow ground water. Deep groundwater lies beneath
the permafrost.
Seasonal frost
Ground surface
Shallow ground water
permafrost
Deep ground water
Perched water table
A perched aquifer is a saturated zone within the zone
of aeration that overlies a confining layer. A perched
aquifer sits above the main water table
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Question ??
• What kind of similarities exists between permafrost-blocked
subsurface water and the perched water table?
• What are the geologic settings which lead to these different
situations ?
Some final thoughts
• Understanding of permafrost-dominated wetlands is very
important because of their vast areal extant.
• Hydrologic processes seen in such wetlands are essential to
understanding their working.
• More field studies can give us better picture of the
hydrologic processes.
• Models of these processes can better our intuitive
understanding and also in collecting more data.
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