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Physical Environment - Soil

 

The Arctic Coastal Plain consists of marine (carried into seas by streams and beach erosion), fluvial (carried by flowing river water), alluvial (carried by river water that gradually loses velocity), and aeolian (carried by wind) deposits from the rising of the Arctic Sea on the plain in the mid/late Quaternary Age.

The Coastal Plain is dominated by lakes and poorly-drained soils, while the Brooks Range has less lakes and more well-drained soils (due to river flow). Poorly-drained soils mostly result from the predominance of permafrost, which restricts water flow in and out of the soil, as well as impermeable bedrock in more upland areas.

 

Active Layer

During the short summers, the active soil layers above the permafrost table thaws briefly to depths of 20-75 cm and allows root penetration, growth and nutrient uptake by the tundra vegetation.

 

Soil Types of the Area

- Pergelic Cryaquepts: low-lying, seasonally flooded, shallow surface mat of partially decomposed organic matter grading into dark gray sandy loam.
- Histic Pergelic Cryaquepts: lowlands, slightly to moderately decomposed organic matter grading into dark green-gray silt loam.
- Pergelic Cryofibrists: poorly-drained, organic, made of thick layer of sedge and moss peat.
- Typic Cryochrepts/ Alfic Cryochrepts/ Aeric Cryochrepts

"Histic" indicates that the soil is shallow with poorly aerated organic material; "Pergelic" refers to temperature "regime," indicating the presence of permafrost; and "Aquept" suggests poor drainage. The soils of the 1002 region are generally loamy, gravelly, and from nearly level to hilly/steep association.

 

Vegetation vs. Soil

Site

Dominant Vegetation

Soil Suborder

Max thaw depth (m)

pH

Tussock Tundra

Eriophorum
Dwarf Shrubs
Sphagnum

Pergelic Histic Cryaquept

.4

6.4

Heath

Dryas
Betula Salix
Ericads

Pergelic
Ruptic Entic
Cryumbrept

2-5+

4.2

Shrub-Lupine

Salix Cassiope Lupinus

Pergelic
Histic Cryaquept

1-2+

6.9

Equisetum

Lupinus
Grasses, Sedges
Equisetum

Pergelic
Histic Cryaquept

.45

7.4

Wet sedge

Carex
Eriophorum

Pergelic
Cryohemist

.55

6.6

Willow

Salix
Betula
Lupinus
Sphagnum

Pergelic
Cryofluvent

+

7.8


(Valentine 1992)

 

pH

The soil pH ranges from approximately 4-8, depending on the soil type, topography, and amount of disturbance to which it was subject. High weathering and cryoturbation generally makes the soil less acidic, introducing more basic materials to the soil matrix. Frost boils, on the other hand, lowered the pH by moving the organic layer deeper in the soil and increasing the depth of thaw. The pH of the soil has a clear relation to the species diversity and density within the area. (Valentine 1992)

 

Element/Nutrient Composition and the Issue of Heat

Arctic soils consist of many trace elements, as well as very large quantities of the carbon, nitrogen, and phosphorous very important to the ecosystem. These elements are essential to processes of mineralization and respiration and nutrient distribution, and because decomposition processes of Arctic tundra soils respond to temperature increase more than other types of region soils, they stand to be very greatly affected by both global warming and other sources of heat input. Increased water flow which can result from melting of permafrost also temporarily increase nutrient distribution and lengthen the growing season for certain plants, particularly E. vaginatum, a species of cottongrass sedges. Increased soil flow increases heat flux, which leads to deeper thaw and therefore magnifies the effect.(Chapin 1988)

Concern also arises that the Arctic soils may contribute to greenhouse gas emissions due to this increase in decomposition of organic matter. Most soil organic carbon is found in the active layer of the soil, and it varies in amount depending on such formations as ice wedges, which melt to form polygons with either "high-centers" or "low-centers" that drain in different ways. The proportion of soil organic carbon in the upper permafrost is directly related to the influence of soil moisture on active-layer thickness in that better drained soils have more carbon in the active layer. With global warming and increased heat, the active layer thickness may increase by 20-30%, increasing cryoturbation, thermal erosion, and intensified thaw-lake cycles. Thaw lakes contain peat in frozen subsoil which would also decompose when melted, increasing emissions.

 

Permafrost

Examining the soil of the 1002 region, one cannot ignore the presence of permafrost, or permanently frozen soil, which underlies 80% of Alaska and remains a central issue in the debate about oil drilling. The surface soils are frozen all but three months of the year, and the permafrost below them penetrate the ground to an average of about 660 m deep.

Permafrost can be either thaw-stable or non thaw-stable, depending on the type and percentage water of the soil it is made of. Permafrost in more fine-grained soils like loess (silty) tend to thaw, sink, and create thermokarsts more often. Permafrost thaws from heat input, such as global warming or human activity, as well as the clearing of vegetation which insulates the ground.

More on permafrost can be found in the Hydrology section

 

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