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Case Study: The Carbon and Water Cycles in Arctic Tundra (What is the…
Case Study: The Carbon and Water Cycles in Arctic Tundra
What is the carbon cycle like in the Tundra?
Permafrost is a vast carbon sink
Globally estimated to contain 1600GT of carbon
Accumulation of carbon is slow
due to the low temperatures which slows down decomposition of dead plant material
The
amount of carbon in soils is 5 times greater than in the above-ground biomass
Flux of carbon is concentrated in the summer months
when the active layer thaws; the plants grow rapidly in the short summer and the long daylight hours allow them to flower and fruit within a few weeks
NPP is <200g/m²/yr
Biomass is small
and ranges between
4 - 29 tonnes/ha
depending on the density of the vegetation cover
During the growing season,
plants input carbon-rich litter to the soil
Activity of
micro-organisms increases and releases CO₂ to the atmosphere through respiration
Not just confined to the summer; even in winter,
unfrozen soil and water in the permafrost act as a source of CO₂ and CH₄
Snow cover may insulate microbial organisms
and allow some
decomposition
despite the low temperatures
Due to global warming,
permafrost is becoming more of a carbon source
(rather than a sink); outputs of carbon from permafrost have increased in recent decades but higher temperatures have increased the growth of plants and there is a greater uptake of CO₂ and this has increased the amount of plant litter entering the store so it is
possible that the cycle has still remained in balance
despite the warming of the Arctic
What is the water cycle like in the Tundra?
Low annual precipitation
(50-350mm) where most of the precipitation is snowfall
Small stores of moisture in the atmosphere
because of low temperatures which reduce absolute humidity
Limited transpiration
becuase of the sparseness of the vegetation cover and the short growing season
Low rates of evaporation
as most of the Sun's energy goes into melting the snow so the ground temperatures remain low and inhibit convection; also surface and soil water are frozen for most of the year
Limited groundwater and moisture stores
; Permafrost is a barrier to infiltration, percolation, recharge and groundwater flow
Accumulation of snow and river/lake ice during the winter months
; there is a sharp increase in river flow after the melting of snow, river and lake ice, and the uppermost active layer of the permafrost in spring and early summer
Extensive wetlands, ponds and lakes on the tundra during the summer;
temporary store of liquid water is due to the permafrost
(which stops drainage)
Changes due to oil and gas production in Alaska
Changes to the
carbon
cycle
Melting of permafrost releases CO₂ and CH₄
On the North Slope, estimated
CO₂ losses from permafrost vary from 7 - 40 million tonnes/year
and
CH₄ losses range from 24,000 - 114,000 tonnes/year
Gas flaring and oil spillages input CO₂
to the atmosphere
Industrial development
Destruction or degrading of tundra vegetation reduces photosynthesis and the uptake of CO₂ from the atmosphere
Thawing of soil increases microbial activity, decompositon and emissions of CO₂
As the vegetation is slow-growing,
regeneration and recovery from damage takes decades
The localised melting of permafrost is associated with:
construction and operation of oil and gas installations, settlements and infrastructure diffusing heat directly to the environment
dust deposition along the rooadsides, creating darkened snow surfaces whcih increases the absorption of sunlight
removal of the vegetation cover which insulates the permafrost
Changes to the
water
cycle
Melting of permafrost and snow cover increases run-off and river discharge
making flooding more likely
In summer, wetlands, ponds and lakes have become more extensive,
increasing evaporation
Strip mining of sand and gravel for construction creates
artificial lakes which disrupt drainage and expose permafrost to more melting
Drainage networks are disrupted by road construction and seismic explosions used to prospect for oil and gas
Water abstracted from creeks and rivers for industrial use and for the building of ice roads in winter, reduces localised run-off
Physical Factors that affect stores and flows of water and carbon
Temperature
In winter,
temperatures prevent evapotranspiration
and in summer, some occurs from standing water, saturated soils and vegetation
Humidity is low all year
Precipitation is sparse
Rock Permeability and Porosity
Permeability is low due to permafrost and crystalline rocks
Due to the
impermeability of the permafrost
, rock permeability, porosity and mineral composition of
rocks have little effect on the cycles
Relief and drainage
During the short summer, the meltwater forms millions of pools and shallow lakes
Drainage is poor so water cannot infiltrate the soil becuase of the permafrost
at depth
Minimal relief (due to years of erosion and weathering) and chaotic glacial deposits obstruct drainage
and contribute to waterlogging in the summer months
Vegetation and Organic Matter in Soil
Carbon is mainly stored as decomposed plant remains in the permafrost
, with most of it
locked away for over 500,000 years
Carbon store of biomass is relatively small as low temperatures, the unavailability of liquid water and few nutrients in parent rocks limit plant growth; averaged over a year,
NPP and photosynthesis are low
Waterlogging and low temperatures slow decomposition, respiration and the flow of CO₂ to the atmosphere
How is the Tundra managed?
How is the melting of permafrost managed?
Are the management strategies having a positive impact on the carbon and water cycle in the Tundra?