role of permafrost in wetland formation - stanford university

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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 ofArctic regions, having a permanently frozen subsoil andsupporting 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°Nlatitude, i.e., 23 1/2° south of the North Pole. It marks thenorthernmost point at which the sun can be seen at the winter solstice(about Dec. 22) and the southernmost point of the northern polarregions at which the midnight sun is visible.

Frost : A deposit of minute ice crystals formed when watervapor condenses at a temperature below freezing.

Permafrost: Permanently frozen subsoil, occurring throughoutthe Polar Regions and locally in perennially frigid areas.

Arctic: A region between the North Pole and the northerntimberlines of North America and Eurasia.

SubArtic: Of or resembling regions just south of the ArcticCircle.

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Temperate: Characterized by moderate temperatures,weather, or climate; neither hot nor cold.

Ice vs. Snow: Falling ice composed of crystals incomplex hexagonal forms. Snow forms mainly whenwater vapor turns directly to ice without going throughthe liquid stage, a process called sublimation.

Thaw: To change from a frozen solid to a liquid bygradual 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) isclose to 0°C before any freezing can occur,

• the freezing of rivers, lakes and oceans is from the top down, soinsulating the water from further freezing and allowing rapidthawing,

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The Role of permafrost and seasonalfrost 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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• What is the climatic variable of most interest?

Difference between precipitation and evapotranspiraton.


• What is the Boreal zone as denoted in the paper?

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• What is the Boreal zone as denoted in the paper?

Southern fringe of the SubAcrtic

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•What is the precipitation trend for our region of interest?


•What is the precipitation trend for our region of interest?

Increases in South-Easterly direction.

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•From the following “hydroperiod” graph, identify where this wetlandis located a) Arctic, b) SubArctic, c) Temperate region ?

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Cold Arctic. Indicated by the permafrost layer startingless than a meter depth.



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Temperate region. Depth of seasonal frost is very less.In some periods of the winter, soil does not freeze at all.


•Where there is no permafrost, which of these have a thicker layer ofseasonal frost and why : a) wetlands, b) mineral-soil terrain ?

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•Where there is no permafrost, which of these have a thicker layer ofseasonal 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.


• In spring, where is thawing rate faster, a) wetlands, b) mineral-soilterrain ?

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• In spring, where is thawing rate faster, a) wetlands, b) mineral-soilterrain ?

Mineral-soil terrain


• In the Boreal zone, it is found that the rate of thawing is more beneaththe frost layer, Why?

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• In the Boreal zone, it is found that the rate of thawing is more beneaththe frost layer, Why?

Because of heat exchange between ground water and peat.


• What is Aufeis ?

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• What is Aufeis ?

Ground water seepage normally freezes as it encounters thecold air at the ground surface creating a layer of ice called Aufeis.


•Can water infiltrate into frozen wetland soils?

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•Can water infiltrate into frozen wetland soils?

Yes. As soil gets colder, water freezes and closes thepores, 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 Runoff Ratio trendPpt - Evap.Figure 2 Figure 3 Figure 7

Processes behind overland flow

An overland flow of water occurring more or lesssimultaneously over a drainage basin when rainfall exceedsthe infiltration capacity of the basin.

Hortonian overland flow:

Saturation Excess Overland Flow:

It is precipitation that cannot be absorbed by the soilbecause the soil is already saturated with water, so itflows across the land surface to a stream or other bodyof water

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Question ??

• In areas of permafrost, spring period is characterized bythawing snow unable to infiltrate the permafrost layer andflowing 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.

Water even crosses drainage divides.Source: San Diego Zoo

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Wetland-Subsurface water interaction

Example 5(A) from Lone Gull, Keewatin.

Areas of permafrost, permafrost serves as confining bedfor shallow ground water. Deep groundwater lies beneaththe permafrost.

Shallow ground water

permafrost

Deep ground water

Ground surface

Seasonal frost

Perched water table

A perched aquifer is a saturated zone within the zoneof aeration that overlies a confining layer. A perchedaquifer sits above the main water table

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• What kind of similarities exists between permafrost-blockedsubsurface water and the perched water table?

• What are the geologic settings which lead to these differentsituations ?

Question ??

• Understanding of permafrost-dominated wetlands is veryimportant because of their vast areal extant.

• Hydrologic processes seen in such wetlands are essential tounderstanding their working.

• More field studies can give us better picture of thehydrologic processes.

• Models of these processes can better our intuitiveunderstanding and also in collecting more data.

Some final thoughts

role of permafrost in wetland formation - stanford university

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